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Developing C and C++ applications in RHEL 9

Red Hat Enterprise Linux 9

Setting up a developer workstation, and developing and debugging C and C++ applications in Red Hat Enterprise Linux 9

Red Hat Customer Content Services

Abstract

Use the different features and utilities available in Red Hat Enterprise Linux 9 to develop and debug C and C++ applications.

Providing feedback on Red Hat documentation
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We are committed to providing high-quality documentation and value your feedback. To help us improve, you can submit suggestions or report errors through the Red Hat Jira tracking system.

Procedure

  1. Log in to the Jira website.

    If you do not have an account, select the option to create one.

  2. Click Create in the top navigation bar.
  3. Enter a descriptive title in the Summary field.
  4. Enter your suggestion for improvement in the Description field. Include links to the relevant parts of the documentation.
  5. Click Create at the bottom of the dialogue.

Chapter 1. Setting up a development workstation
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Red Hat Enterprise Linux 9 supports the development of custom applications. To set up your system for development, install the required tools and utilities for the most common development use cases.

1.1. Enabling debug and source repositories
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To access essential debugging data for system components, enable debug and source repositories. RHEL disables these by default to save space. Enable them to install debuginfo packages required for performance measurement and deep system troubleshooting.

Procedure

  • Enable the source and debug information package channels:

    1. Enable the BaseOS debug repository: 

      # subscription-manager repos --enable rhel-9-for-$(uname -i)-baseos-debug-rpms

    2. Enable the BaseOS source repository: 

      # subscription-manager repos --enable rhel-9-for-$(uname -i)-baseos-source-rpms

    3. Enable the AppStream debug repository: 

      # subscription-manager repos --enable rhel-9-for-$(uname -i)-appstream-debug-rpms

    4. Enable the AppStream source repository: 

      # subscription-manager repos --enable rhel-9-for-$(uname -i)-appstream-source-rpms

      + The $(uname -i) part is automatically replaced with a matching value for architecture of your system:

Expand

Architecture name

Value

64-bit Intel and AMD

x86_64

64-bit ARM

aarch64

IBM POWER

ppc64le

64-bit IBM Z

s390x

1.2. Setting up to manage application versions
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Effective version control is essential to all multi-developer projects. Red Hat Enterprise Linux includes Git, a distributed version control system.

Procedure

  1. Install the git package: 

    # dnf install git

  2. Optional: Set the full name associated with your Git commits: 

    $ git config --global user.name "Full Name"

  3. Optional: Set the email address associated with your Git commits: 

    $ git config --global user.email "email@example.com"

    Replace Full Name and email@example.com with your actual name and email address.

  4. Optional: To change the default text editor started by Git, set value of the core.editor configuration option: 

    $ git config --global core.editor command

    Replace command with the command to be used to start the selected text editor.

To develop C and C++ applications on Red Hat Enterprise Linux, you can use the development tools provided by Red Hat Enterprise Linux. This procedure describes how to install the standard development tools, including the GCC and LLVM toolchains.

Prerequisites

  • The debug and source repositories must be enabled.

Procedure

  1. Install the Development Tools package group including GNU Compiler Collection (GCC), GNU Debugger (GDB), and other development tools: 

    # dnf group install "Development Tools"

  2. Install the LLVM-based toolchain including the clang compiler and lldb debugger: 

    # dnf install llvm-toolset

  3. Optional: For Fortran dependencies, install the GNU Fortran compiler: 

    # dnf install gcc-gfortran

1.4. Setting up to debug applications
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To analyze and troubleshoot internal application behavior, Red Hat Enterprise Linux offers multiple debugging and instrumentation tools.

Prerequisites

  • The debug and source repositories must be enabled.

Procedure

  1. Install the tools useful for debugging: 

    # dnf install gdb valgrind systemtap ltrace strace

  2. Install the dnf-utils package in order to use the debuginfo-install tool: 

    # dnf install dnf-utils

  3. Run a SystemTap helper script for setting up the environment. 

    # stap-prep

    Note that stap-prep installs packages relevant to the currently running kernel, which might not be the same as the actually installed kernel(s). To ensure stap-prep installs the correct kernel-debuginfo and kernel-headers packages, double-check the current kernel version by using the uname -r command and reboot your system if necessary.

  4. Make sure SELinux policies allow the relevant applications to run not only normally, but in the debugging situations, too. For more information, see Using SELinux.

To identify the causes of application performance loss, you can use the performance measurement tools provided by Red Hat Enterprise Linux. This procedure describes how to install tools such as perf, Valgrind, SystemTap, and Performance Co-Pilot (PCP).

Prerequisites

  • The debug and source repositories must be enabled.

Procedure

  1. Install the tools for performance measurement: 

    # dnf install perf papi pcp-zeroconf valgrind strace sysstat systemtap

  2. Run a SystemTap helper script for setting up the environment. 

    # stap-prep

    Note that stap-prep installs packages relevant to the currently running kernel, which might not be the same as the actually installed kernel(s). To ensure stap-prep installs the correct kernel-debuginfo and kernel-headers packages, double-check the current kernel version by using the uname -r command and reboot your system if necessary.

  3. Enable the Performance Co-Pilot (PCP) collector service: 

    # systemctl enable pmcd

  4. Start the Performance Co-Pilot (PCP) collector service: 

    # systemctl start pmcd

Chapter 2. Creating C or C++ Applications
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Learn how to build C and C++ code with GCC, use and create libraries, and manage builds with Make.

2.1. GCC in RHEL 9
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Red Hat Enterprise Linux 9 is distributed with the GNU Compiler Collection (GCC) 11 as the standard compiler.

The default language standard setting for GCC 11 is C++17. This is equivalent to explicitly using the command-line option -std=gnu++17.

Later language standards, such as C++20 and so on, and library features introduced in these later language standards are still considered experimental.

2.2. Building code with GCC
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Learn about situations where source code must be transformed into executable code.

2.2.1. Relationship between code forms
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The C and C++ languages have three forms of code that are created through different stages of the build process. Understanding these relationships helps you work effectively with the GNU Compiler Collection (GCC).

Prerequisites

  • Understanding the concepts of compiling and linking

Possible code forms

The code forms of C and C++ languages:

  • Source code written in the C or C++ language, present as plain text files.

    The files typically use extensions such as .c, .cc, .cpp, .h, .hpp, .i, .inc. For a complete list of supported extensions and their interpretation, see the gcc manual pages: 

    $ man gcc

  • Object code, created by compiling the source code with a compiler. This is an intermediate form.

    The object code files use the .o extension.

  • Executable code, created by linking object code with a linker.

    Linux application executable files do not use any file name extension. Shared object (library) executable files use the .so file name extension.

Note

Library archive files for static linking also exist. This is a variant of object code that uses the .a file name extension. Static linking is not recommended. See Section 2.3.2, “Static and dynamic linking”.

Handling of code forms in GCC

Producing executable code from source code is performed in two steps, which require different applications or tools. GCC can be used as an intelligent driver for both compilers and linkers. This allows you to use a single gcc command for any of the required actions (compiling and linking). GCC automatically selects the actions and their sequence:

  1. Source files are compiled to object files.
  2. Object files and libraries are linked (including the previously compiled sources).

It is possible to run GCC so that it performs only compiling, only linking, or both compiling and linking in a single step. This is determined by the types of inputs and requested type of output(s).

Because larger projects require a build system which usually runs GCC separately for each action, it is better to always consider compilation and linking as two distinct actions, even if GCC can perform both at once.

2.2.2. Compiling source files to object code
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To compile source files into object files without creating an executable, use GCC’s -c option.

Prerequisites

  • C or C++ source code file(s)
  • GCC installed on the system

Procedure

  1. Change to the directory containing the source code file(s).

  2. Run gcc with the -c option: 

    $ gcc -c source.c another_source.c

    Object files are created, with their file names reflecting the original source code files: source.c results in source.o.

    Note

    With C++ source code, replace the gcc command with g++ for convenient handling of C++ Standard Library dependencies.

To debug C and C++ applications effectively, generate debugging information during compilation. Use GCC’s -g option to create this data. Debuggers use this data to map executable code to source lines for inspecting variables and logic.

Prerequisites

  • You have the gcc package installed.

Procedure

  1. Compile and link your code with the -g option to generate debugging information: 

    $ gcc ... -g ...

  2. Optional: Set the optimization level to -Og: 

    $ gcc ... -g -Og ...

    Compiler optimizations can make executable code hard to relate to the source code. The -Og option optimizes the code without interfering with debugging. However, be aware that changing optimization levels can alter the program’s behavior.

  3. Optional: Use -g for moderate debugging information, or -g3 to include macro definitions: 

    $ gcc ... -g3 ...

Verification

  • Test the code by using the -fcompare-debug GCC option: 

    $ gcc -fcompare-debug ...

    This option tests code compiled with and without debug information. If the resulting binaries are identical, the executable code is not affected by debugging options. By using the -fcompare-debug option significantly increases compilation time.

2.2.4. Code optimization with the GCC
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A single program can be transformed into more than one sequence of machine instructions. You can achieve better performance, such as faster execution speed, greater resource efficiency, or smaller file size, if you allocate more resources to analyzing the code during compilation.

With the GNU Compiler Collection (GCC), you can set the optimization level using the -Olevel option. This option accepts a set of values in place of the level.

Expand
LevelDescription

0

Optimize for compilation speed - no code optimization (default).

1, 2, 3

Optimize to increase code execution speed (the larger the number, the greater the speed).

s

Optimize for file size.

fast

Same as a level 3 setting, plus fast disregards strict standards compliance to allow for additional optimizations.

g

Optimize for debugging experience.

For release builds, use the optimization option -O2.

During development, the -Og option is useful for debugging the program or library in some situations. Because some bugs manifest only with certain optimization levels, test the program or library with the release optimization level.

GCC offers a large number of options to enable individual optimizations. For more information, see the following Additional resources.

2.2.5. Options for hardening code with the GCC
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To add security checks during code compilation, you can use GNU Compiler Collection (GCC) compiler options. This helps produce more secure programs and libraries without changing source code.

Release version options

The following list of options is the recommended minimum for developers targeting Red Hat Enterprise Linux:

+ 

$ gcc ... -O2 -g -Wall -Wl,-z,now,-z,relro -fstack-protector-strong -fstack-clash-protection -D_FORTIFY_SOURCE=2 ...
  • For programs, add the -fPIE and -pie Position Independent Executable options.
  • For dynamically linked libraries, the mandatory -fPIC (Position Independent Code) option indirectly increases security.

Development options

Use the following options to detect security flaws during development. Use these options in conjunction with the options for the release version:

+ 

$ gcc ... -Walloc-zero -Walloca-larger-than -Wextra -Wformat-security -Wvla-larger-than ...

Additional resources

2.2.6. Linking code to create executable files
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Linking is the final step when building a C or C++ application. Linking combines all object files and libraries into an executable file.

Prerequisites

  • One or more object file(s)
  • GCC must be installed on the system

Procedure

  1. Change to the directory containing the object code file(s).

  2. Run gcc: 

    $ gcc ... objfile.o another_object.o ... -o executable-file

    An executable file named executable-file is created from the supplied object files and libraries.

    To link additional libraries, add the required options after the list of object files.

    Note

    With C++ source code, replace the gcc command with g++ for convenient handling of C++ Standard Library dependencies.

To build a simple sample C program, you can use the GNU Compiler Collection (GCC). In this example, compiling and linking the code is done in one step.

Prerequisites

  • You must understand how to use GCC.

Procedure

  1. Create a directory hello-c and change to it: 

    $ mkdir hello-c
$ cd hello-c

  2. Create file hello.c with the following contents: 

    #include <stdio.h>

int main() {
  printf("Hello, World!\n");
  return 0;
}

  3. Compile and link the code with GCC: 

    $ gcc hello.c -o helloworld

    This compiles the code, creates the object file hello.o, and links the executable file helloworld from the object file.

  4. Run the resulting executable file: 

    $ ./helloworld
Hello, World!

To build a simple sample C program, you can use the GNU Compiler Collection (GCC). In this example, compiling and linking the code are two separate steps.

Prerequisites

  • You must understand how to use GCC.

Procedure

  1. Create a directory hello-c and change to it: 

    $ mkdir hello-c
$ cd hello-c

  2. Create file hello.c with the following contents: 

    #include <stdio.h>

int main() {
  printf("Hello, World!\n");
  return 0;
}

  3. Compile the code with GCC: 

    $ gcc -c hello.c

    The object file hello.o is created.

  4. Link an executable file helloworld from the object file: 

    $ gcc hello.o -o helloworld

  5. Run the resulting executable file: 

    $ ./helloworld
Hello, World!

To build a sample minimal C++ program, you can use the GNU Compiler Collection (GCC). In this example, compiling and linking the code is done in one step.

Prerequisites

  • You must understand the difference between gcc and g++.

Procedure

  1. Create a directory hello-cpp and change to it: 

    $ mkdir hello-cpp
$ cd hello-cpp

  2. Create file hello.cpp with the following contents: 

    #include <iostream>

int main() {
  std::cout << "Hello, World!\n";
  return 0;
}

  3. Compile and link the code with g++: 

    $ g++ hello.cpp -o helloworld

    This compiles the code, creates the object file hello.o, and links the executable file helloworld from the object file.

  4. Run the resulting executable file: 

    $ ./helloworld
Hello, World!

To build a minimal C++ program by using a two-step process, you can use the GNU Compiler Collection (GCC). First, compile the source into an object file, then link it to create the executable. This example demonstrates modular building with the GCC compiler.

Prerequisites

  • You must understand the difference between gcc and g++.

Procedure

  1. Create a directory hello-cpp and change to it: 

    $ mkdir hello-cpp
$ cd hello-cpp

  2. Create file hello.cpp with the following contents: 

    #include <iostream>

int main() {
  std::cout << "Hello, World!\n";
  return 0;
}

  3. Compile the code with g++: 

    $ g++ -c hello.cpp

    The object file hello.o is created.

  4. Link an executable file helloworld from the object file: 

    $ g++ hello.o -o helloworld

  5. Run the resulting executable file: 

    $ ./helloworld
Hello, World!

2.3. Using Libraries with the GCC
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Learn about using libraries in code.

2.3.1. Library naming conventions
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System libraries require consistent naming. A library known as foo is expected to exist as file libfoo.so or libfoo.a. This convention is automatically understood by the linking input options of the GNU Compiler Collection (GCC), but not by the output options:

  • When linking against the library, the library can be specified only by its name foo with the -l option as -lfoo: 

    $ gcc ... -lfoo ...
  • When creating the library, the full file name libfoo.so or libfoo.a must be specified.

2.3.2. Static and dynamic linking
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When building C or C++ applications, you must use dynamic linking. Static linking reduces compatibility and prevents timely library security updates.

Comparison of static and dynamic linking

Static linking makes libraries part of the resulting executable file. Dynamic linking keeps these libraries as separate files.

Dynamic and static linking can be compared in several ways:

Resource use

Static linking results in larger executable files which contain more code. This additional code coming from libraries cannot be shared across multiple programs on the system, increasing file system usage and memory usage at run time. Multiple processes running the same statically linked program will still share the code.

Conversely, static applications need fewer runtime relocations, leading to reduced startup time, and require less private resident set size (RSS) memory. Generated code for static linking can be more efficient than for dynamic linking due to the performance cost of position-independent code (PIC).

Security
Dynamically linked libraries which provide ABI compatibility can be updated without changing the executable files depending on these libraries. This is especially important for libraries provided by Red Hat as part of Red Hat Enterprise Linux, where Red Hat provides security updates. Static linking against any such libraries is strongly discouraged.
Compatibility

Static linking might seem to provide executable files independent of the versions of libraries provided by the operating system. However, most libraries depend on other libraries. With static linking, this dependency becomes inflexible and as a result, both forward and backward compatibility is lost. Static linking is guaranteed to work only on the system where the executable file was built.

Warning

Applications linking statically libraries from the GNU C library (glibc) still require glibc to be present on the system as a dynamic library. Furthermore, the dynamic library variant of glibc available at the application’s run time must be a bitwise identical version to that present while linking the application. As a result, static linking is guaranteed to work only on the system where the executable file was built.

Support coverage
Most static libraries provided by Red Hat are in the CodeReady Linux Builder channel and not supported by Red Hat.
Functionality

Some libraries, notably the GNU C Library (glibc), offer reduced functionality when linked statically.

For example, when statically linked, glibc does not support threads and any form of calls to the dlopen() function in the same program.

As a result of the listed disadvantages, static linking should be avoided at all costs, particularly for whole applications and the glibc and libstdc++ libraries.

Cases for static linking

Static linking might be a reasonable choice in some cases, such as:

  • Using a library which is not enabled for dynamic linking.
  • Fully static linking can be required for running code in an empty chroot environment or container. However, static linking using the glibc-static package is not supported by Red Hat.

2.3.3. Using a library with the GCC
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A library is a package of code which can be reused in your program. A C or C++ library consists of two parts:

  • The library code
  • Header files

Compiling code that uses a library

The header files describe the interface of the library: the functions and variables available in the library. Information from the header files is needed for compiling the code.

Typically, header files of a library will be placed in a different directory than your application’s code. To tell the GNU Compiler Collection (GCC) where the header files are, use the -I option: 

$ gcc ... -Iinclude_path ...

Replace include_path with the actual path to the header file directory.

The -I option can be used multiple times to add multiple directories with header files. When looking for a header file, these directories are searched in the order of their appearance in the -I options.

Linking code that uses a library

When linking the executable file, both the object code of your application and the binary code of the library must be available. The code for static and dynamic libraries is present in different forms:

  • Static libraries are available as archive files. They contain a group of object files. The archive file has a file name extension .a.
  • Dynamic libraries are available as shared objects. They are a form of an executable file. A shared object has a file name extension .so.

To tell GCC where the archives or shared object files of a library are, use the -L option:

+ 

$ gcc ... -Llibrary_path -lfoo ...

Replace library_path with the actual path to the library directory.

The -L option can be used multiple times to add multiple directories. When looking for a library, these directories are searched in the order of their -L options.

The order of options matters: GCC cannot link against a library foo unless it knows the directory with this library. Therefore, use the -L options to specify library directories before using the -l options for linking against libraries.

Compiling and linking code which uses a library in one step

When the situation allows the code to be compiled and linked in one gcc command, use the options for both situations mentioned above at once.

2.3.4. Linking static libraries with the GCC
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To link static libraries, bundle them as archives that contain object files. After linking, they become part of the resulting executable file. Static linking overrides the default dynamic linking behavior.

Note

Red Hat discourages static linking for security reasons. See Section 2.3.2, “Static and dynamic linking”. Use static linking only when necessary, especially against libraries provided by Red Hat.

Prerequisites

  • GCC is installed on your system.
  • You have a specific static library (e.g., libfoo.a) and no dynamic version (libfoo.so) available.
Note

Most libraries in Red Hat support dynamic linking only. These steps apply to libraries not enabled for dynamic linking.

Procedure

  1. Compile the program source files with headers of the static library: 

    $ gcc ... -Iheader_path -c ...

    Replace header_path with the directory path containing the header files.

  2. Link the program with the static library: 

    $ gcc ... -Llibrary_path -lfoo ...

    Replace library_path with the directory path containing the file libfoo.a.

  3. Run the program: 

    $ ./program
Warning

The -static option forbids all dynamic linking. Use -Wl,-Bstatic and -Wl,-Bdynamic to control linker behavior more precisely. See Section 2.3.6, “Static and dynamic libraries with GCC”.

2.3.5. Using a dynamic library with the GCC
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Dynamic libraries are available as standalone executable files, required at both linking time and run time. They stay independent of your application’s executable file.

Prerequisites

  • GCC must be installed on the system.
  • A set of source or object files forming a valid program, requiring some dynamic library foo and no other libraries.

  • The foo library must be available as a file libfoo.so.

    Linking a program against a dynamic library
    To link a program against a dynamic library foo: 
$ gcc ... -Llibrary_path -lfoo ...

When a program is linked against a dynamic library, the resulting program must always load the library at run time. There are two options for locating the library:

  • Using a rpath value stored in the executable file itself

  • Using the LD_LIBRARY_PATH variable at run time

    Using a rpath value stored in the executable file
    The rpath is a special value saved as a part of an executable file when it is being linked. Later, when the program is loaded from its executable file, the runtime linker will use the rpath value to locate the library files.

While linking with the GNU Compiler Collection (GCC), to store the path library_path as rpath: 

$ gcc ... -Llibrary_path -lfoo -Wl,-rpath=library_path ...

The path library_path must point to a directory containing the file libfoo.so.

Important

Do not add a space after the comma in the -Wl,-rpath= option.

To run the program later: 

$ ./program
Using the LD_LIBRARY_PATH environment variable
If no rpath is found in the program’s executable file, the runtime linker will use the LD_LIBRARY_PATH environment variable. The value of this variable must be changed for each program. This value should represent the path where the shared library objects are located.

To run the program without rpath set, with libraries present in path library_path: 

$ export LD_LIBRARY_PATH=library_path:$LD_LIBRARY_PATH
$ ./program

Leaving out the rpath value offers flexibility, but requires setting the LD_LIBRARY_PATH variable every time the program is to run.

Placing the library into the default directories
The runtime linker configuration specifies several directories as a default location of dynamic library files. To use this default behaviour, copy your library to the appropriate directory.

For full details on the dynamic linker behavior, see the following resources:

  • Linux manual pages for the dynamic linker: 

    $ man ld.so

  • Contents of the /etc/ld.so.conf configuration file: 

    $ cat /etc/ld.so.conf

  • Report of the libraries recognized by the dynamic linker without additional configuration, which includes the directories: 

    $ ldconfig -v

2.3.6. Static and dynamic libraries with GCC
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Combining static and dynamic linking balances portability and efficiency. GCC automatically selects shared objects over static archives unless configured otherwise. Understand this behavior to control exactly which library versions your application uses.

Prerequisites

  • Understanding static and dynamic linking

Introduction

gcc recognizes both dynamic and static libraries. When the -lfoo option is encountered, gcc will first attempt to locate a shared object (a .so file) containing a dynamically linked version of the foo library, and then look for the archive file (.a) containing a static version of the library. Thus, the following situations can result from this search:

  • Only the shared object is found, and gcc links against it dynamically.
  • Only the archive is found, and gcc links against it statically.
  • Both the shared object and archive are found, and by default, gcc selects dynamic linking against the shared object.
  • Neither shared object nor archive is found, and linking fails.

Because of these rules, the best way to select the static or dynamic version of a library for linking is having only that version found by gcc. This can be controlled to some extent by using or leaving out directories containing the library versions, when specifying the -Lpath options.

Additionally, because dynamic linking is the default, the only situation where linking must be explicitly specified is when a library with both versions present should be linked statically. There are two possible resolutions:

  • Specifying the static libraries by file path instead of the -l option
  • Using the -Wl option to pass options to the linker

Specifying the static libraries by file

Usually, gcc is instructed to link against the foo library with the -lfoo option. However, it is possible to specify the full path to file libfoo.a containing the library instead: 

$ gcc ... path/to/libfoo.a ...

From the file extension .a, gcc will understand that this is a library to link with the program. However, specifying the full path to the library file is a less flexible method.

Using the -Wl option

The gcc option -Wl is a special option for passing options to the underlying linker. Syntax of this option differs from the other gcc options. The -Wl option is followed by a comma-separated list of linker options, while other gcc options require space-separated list of options.

The ld linker used by gcc offers the options -Bstatic and -Bdynamic to specify whether libraries following this option should be linked statically or dynamically. After passing -Bstatic and a library to the linker, the default dynamic linking behaviour must be restored manually for the following libraries to be linked dynamically with the -Bdynamic option.

To link a program, link library first statically (libfirst.a) and second dynamically (libsecond.so): 

$ gcc ... -Wl,-Bstatic -lfirst -Wl,-Bdynamic -lsecond ...
Note

gcc can be configured to use linkers other than the default ld.

2.4. Creating libraries with the GCC
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Learn about the steps to creating libraries and the necessary concepts used by the Linux operating system for libraries.

2.4.1. Library naming conventions
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System libraries require consistent naming. A library known as foo is expected to exist as file libfoo.so or libfoo.a. This convention is automatically understood by the linking input options of the GNU Compiler Collection (GCC), but not by the output options:

  • When linking against the library, the library can be specified only by its name foo with the -l option as -lfoo: 

    $ gcc ... -lfoo ...
  • When creating the library, the full file name libfoo.so or libfoo.a must be specified.

2.4.2. The Soname mechanism
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To manage multiple compatible versions of a library, dynamically loaded libraries (shared objects) use the soname mechanism.

Prerequisites

  • You must understand dynamic linking and libraries.
  • You must understand the concept of ABI compatibility.
  • You must understand library naming conventions.

  • You must understand symbolic links.

    Problem introduction
    A dynamically loaded library (shared object) exists as an independent executable file. This makes it possible to update the library without updating the applications that depend on it. However, the following problems arise with this concept:
  • Identification of the actual version of the library
  • Need for multiple versions of the same library present

  • Signalling ABI compatibility of each of the multiple versions

    Soname mechanism
    To resolve this, Linux uses a mechanism called soname.

A foo library version X.Y is ABI-compatible with other versions with the same value of X in a version number. Minor changes preserving compatibility increase the number Y. Major changes that break compatibility increase the number X.

The actual foo library version X.Y exists as a file libfoo.so.x.y. Inside the library file, a soname is recorded with value libfoo.so.x to signal the compatibility.

When applications are built, the linker looks for the library by searching for the file libfoo.so. A symbolic link with this name must exist, pointing to the actual library file. The linker then reads the soname from the library file and records it into the application executable file. Finally, the linker creates the application that declares dependency on the library using the soname, not a name or a file name.

When the runtime dynamic linker links an application before running, it reads the soname from application’s executable file. This soname is libfoo.so.x. A symbolic link with this name must exist, pointing to the actual library file. This allows loading the library, regardless of the Y component of a version, because the soname does not change.

Note

The Y component of the version number is not limited to just a single number. Additionally, some libraries encode their version in their name.

Reading soname from a file
To display the soname of a library file somelibrary: 
$ objdump -p somelibrary | grep SONAME

Replace somelibrary with the actual file name of the library that you want to examine.

2.4.3. Creating dynamic libraries with the GCC
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To build and install a dynamic library from the source code, you can use the GNU Compiler Collection (GCC). Dynamically linked libraries, also known as shared objects, help you conserve resources by reusing code and increase security by making library updates easier.

Prerequisites

  • You must understand the soname mechanism.
  • GCC must be installed on the system.
  • You must have source code for a library.

Procedure

  1. Change to the directory with library sources.

  2. Compile each source file to an object file with the Position independent code option -fPIC: 

    $ gcc ... -c -fPIC some_file.c ...

    The object files have the same file names as the original source code files, but their extension is .o.

  3. Link the shared library from the object files: 

    $ gcc -shared -o libfoo.so.x.y -Wl,-soname,libfoo.so.x some_file.o ...

    The used major version number is X and minor version number Y.

  4. Copy the libfoo.so.x.y file to an appropriate location, where the system’s dynamic linker can find it. On Red Hat Enterprise Linux, the directory for libraries is /usr/lib64: 

    # cp libfoo.so.x.y /usr/lib64

    Note that you need root permissions to manipulate files in this directory.

  5. Create the symlink structure for soname mechanism: 

    # ln -s libfoo.so.x.y libfoo.so.x
# ln -s libfoo.so.x libfoo.so

Additional resources

2.4.4. Creating static libraries
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To create static libraries, bundle object files into an archive by using the ar utility. Use the resulting .a file for static linking and for distributing self-contained libraries without external dependencies.

Note

Red Hat discourages the use of static linking for security reasons. Use static linking only when necessary, especially against libraries provided by Red Hat. See Section 2.3.2, “Static and dynamic linking” for more details.

Prerequisites

  • GCC and binutils must be installed on the system.
  • You must understand static and dynamic linking.
  • Source file(s) with functions to be shared as a library are available.

Procedure

  1. Create intermediate object files with GCC. 

    $ gcc -c source_file.c ...

    Append more source files if required. The resulting object files share the file name but use the .o file name extension.

  2. Turn the object files into a static library (archive) using the ar tool from the binutils package. 

    $ ar rcs libfoo.a source_file.o ...

    File libfoo.a is created.

  3. Use the nm command to inspect the resulting archive: 

    $ nm libfoo.a
  4. Copy the static library file to the appropriate directory.

  5. When linking against the library, GCC will automatically recognize from the .a file name extension that the library is an archive for static linking. 

    $ gcc ... -lfoo ...

2.5. Managing More Code with Make
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The GNU make utility, commonly abbreviated make, is a tool for controlling the generation of executables from source files. make automatically determines which parts of a complex program have changed and need to be recompiled. make uses configuration files called Makefiles to control the way programs are built.

2.5.1. GNU make and Makefile overview
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To build executable programs and libraries from source code, and to record and repeat the steps if required, Red Hat Enterprise Linux contains the GNU’s Not Unix (GNU) make command.

GNU make

GNU make reads Makefiles which contain the instructions describing the build process. A Makefile contains multiple rules that describe a way to satisfy a certain condition (target) with a specific action (recipe). Rules can hierarchically depend on another rule.

Running make without any options makes it look for a Makefile in the current directory and attempt to reach the default target. The actual Makefile file name can be one of Makefile, makefile, and GNUmakefile. The default target is determined from the Makefile contents.

Makefile details

Makefiles use a relatively simple syntax for defining variables and rules, which consists of a target and a recipe. The target specifies what is the output if a rule is executed. The lines with recipes must start with the TAB character.

Typically, a Makefile contains rules for compiling source files, a rule for linking the resulting object files, and a target that serves as the entry point at the top of the hierarchy.

Consider the following Makefile for building a C program which consists of a single file, hello.c. 

all: hello

hello: hello.o
        gcc hello.o -o hello

hello.o: hello.c
        gcc -c hello.c -o hello.o

This example shows that to reach the target all, file hello is required. To get hello, one needs hello.o (linked by gcc), which in turn is created from hello.c (compiled by gcc).

The target all is the default target because it is the first target that does not start with a period (.). Running make without any arguments is then identical to running make all, when the current directory contains this Makefile.

Typical makefile

A more typical Makefile uses variables for generalization of the steps and adds a target "clean" - remove everything but the source files. 

CC=gcc
CFLAGS=-c -Wall
SOURCE=hello.c
OBJ=$(SOURCE:.c=.o)
EXE=hello

all: $(SOURCE) $(EXE)

$(EXE): $(OBJ)
        $(CC) $(OBJ) -o $@

%.o: %.c
        $(CC) $(CFLAGS) $< -o $@

clean:
        rm -rf $(OBJ) $(EXE)

Adding more source files to such Makefile requires only adding them to the line where the SOURCE variable is defined.

To automate C program builds and manage compilation dependencies efficiently, use a Makefile. Create a script that streamlines repetitive tasks to establish a consistent and reliable build process.

Prerequisites

  • You must understand the concepts of Makefiles and make.

Procedure

  1. Create a directory hellomake: 

    $ mkdir hellomake

  2. Change to the hellomake directory: 

    $ cd hellomake

  3. Create a file hello.c with the following contents: 

    #include <stdio.h>

int main(int argc, char *argv[]) {
  printf("Hello, World!\n");
  return 0;
}

  4. Create a file Makefile with the following contents: 

    CC=gcc
CFLAGS=-c -Wall
SOURCE=hello.c
OBJ=$(SOURCE:.c=.o)
EXE=hello

all: $(SOURCE) $(EXE)

$(EXE): $(OBJ)
        $(CC) $(OBJ) -o $@

%.o: %.c
        $(CC) $(CFLAGS) $< -o $@

clean:
        rm -rf $(OBJ) $(EXE)
    Important

    The Makefile recipe lines must start with the tab character! When copying the text above from the documentation, the cut-and-paste process may paste spaces instead of tabs. If this happens, correct the issue manually.

  5. Run make: 

    $ make
     
    $ gcc -c -Wall hello.c -o hello.o
$ gcc hello.o -o hello

    This creates an executable file hello.

  6. Run the executable file hello: 

    $ ./hello
     
    Hello, World!

  7. Run the Makefile target clean to remove the created files: 

    $ make clean
     
    # rm -rf hello.o hello

2.5.3. Documentation resources for make
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To find more information about make, see the following resources.

Installed documentation

  • Use the man and info tools to view manual pages and information pages installed on your system.

    1. View the make manual page: 
$ man make
  1. View the make information page: 
$ info make
Online documentation

Chapter 3. Debugging Applications
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Enable debugging, inspect application state with GDB, record interactions, and debug crashed applications.

3.1. Enabling Debugging with Debugging Information
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To debug applications and libraries, debugging information is required. The following sections describe how to obtain this information.

3.1.1. Debugging information
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Reliable debugging requires connecting binary code back to source code. Debugging information provides this link, essential for inspecting variables and execution flow. The GNU Compiler Collection (GCC) generates this data in the DWARF format within ELF files, which tools like the GNU Debugger (GDB) use to analyze program behavior.

Red Hat Enterprise Linux uses the ELF format for executable binaries, shared libraries, or debuginfo files. Within these ELF files, the DWARF format is used to hold the debug information.

To display DWARF information stored within an ELF file, run the readelf -w file command.

Important

STABS is an older, less capable format, occasionally used with UNIX. Its use is discouraged by Red Hat. GCC and GDB provide STABS production and consumption on a best effort basis only. Some other tools such as Valgrind and elfutils do not work with STABS.

To debug C and C++ applications effectively, generate debugging information during compilation. Use GCC’s -g option to create this data. Debuggers use this data to map executable code to source lines for inspecting variables and logic.

Prerequisites

  • You have the gcc package installed.

Procedure

  1. Compile and link your code with the -g option to generate debugging information: 

    $ gcc ... -g ...

  2. Optional: Set the optimization level to -Og: 

    $ gcc ... -g -Og ...

    Compiler optimizations can make executable code hard to relate to the source code. The -Og option optimizes the code without interfering with debugging. However, be aware that changing optimization levels can alter the program’s behavior.

  3. Optional: Use -g for moderate debugging information, or -g3 to include macro definitions: 

    $ gcc ... -g3 ...

Verification

  • Test the code by using the -fcompare-debug GCC option: 

    $ gcc -fcompare-debug ...

    This option tests code compiled with and without debug information. If the resulting binaries are identical, the executable code is not affected by debugging options. By using the -fcompare-debug option significantly increases compilation time.

3.1.3. Debuginfo and debugsource packages
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The debuginfo and debugsource packages contain debugging information and source code for programs and libraries. To debug Red Hat Enterprise Linux applications, install these packages from additional repositories.

Debugging information package types

There are two types of packages available for debugging:

Debuginfo packages
The debuginfo packages provide debugging information needed to provide human-readable names for binary code features. These packages contain .debug files, which contain DWARF debugging information. These files are installed to the /usr/lib/debug directory.
Debugsource packages
The debugsource packages contain the source files used for compiling the binary code. With both debuginfo and debugsource packages installed, debuggers such as GDB or LLDB can relate the execution of binary code to the source code. The source code files are installed to the /usr/src/debug directory.

To obtain the necessary debuginfo packages for troubleshooting installed applications or libraries, use the GNU Debugger (GDB). It automatically detects missing symbols and identifies the specific packages needed. Follow GDB’s recommendations to install these packages and enable full debugging capabilities.

Prerequisites

  • The application or library you want to debug must be installed on the system.
  • GDB and the debuginfo-install tool must be installed on the system. For details, see Setting up to debug applications.
  • Repositories providing debuginfo and debugsource packages must be configured and enabled on the system. For details, see Enabling debug and source repositories.

Procedure

  1. Start GDB attached to the application or library you want to debug. GDB automatically recognizes missing debugging information and suggests a command to run. 

    $ gdb -q /bin/ls
     
    Reading symbols from /bin/ls...Reading symbols from .gnu_debugdata for /usr/bin/ls...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Missing separate debuginfos, use: dnf debuginfo-install coreutils-8.30-6.el8.x86_64
(gdb)

  2. Exit GDB: type q and confirm with Enter. 

    (gdb) q

  3. Run the command suggested by GDB to install the required debuginfo packages: 

    # dnf debuginfo-install coreutils-8.30-6.el8.x86_64

    The dnf package management tool provides a summary of the changes, asks for confirmation and once you confirm, downloads and installs all the necessary files.

  4. In case GDB is not able to suggest the debuginfo package, follow the procedure described in Getting debuginfo packages for an application or library manually.

To manually determine which debuginfo packages you need to install, locate the executable file and find the package that installs it.

Note

Red Hat recommends that you use GDB to determine the packages for installation. Use this manual procedure only if GDB is not able to suggest the package to install.

Prerequisites

  • The application or library must be installed on the system.
  • The application or library was installed from a package.
  • The debuginfo-install tool must be available on the system.
  • Channels providing the debuginfo packages must be configured and enabled on the system.

Procedure

  1. Find the executable file of the application or library.

    1. Use the which command to find the application file. 

      $ which less
       
      /usr/bin/less

    2. Use the locate command to find the library file. 

      $ locate libz | grep so
       
      /usr/lib64/libz.so.1
/usr/lib64/libz.so.1.2.11

      If the original reasons for debugging include error messages, pick the result where the library has the same additional numbers in its file name as those mentioned in the error messages. If in doubt, try following the rest of the procedure with the result where the library file name includes no additional numbers.

      Note

      The locate command is provided by the mlocate package. To install it and enable its use:

      1. Install the mlocate package: 

        # dnf install mlocate

      2. Update the database: 

        # updatedb

  2. Search for a name and version of the package that provided the file: 

    $ rpm -qf /usr/lib64/libz.so.1.2.7
     
    zlib-1.2.11-10.el8.x86_64

    The output provides details for the installed package in the name:epoch-version.release.architecture format.

    Important

    If this step does not produce any results, it is not possible to determine which package provided the binary file. There are several possible cases:

    • The file is installed from a package which is not known to package management tools in their current configuration.
    • The file is installed from a locally downloaded and manually installed package. Determining a suitable debuginfo package automatically is impossible in that case.
    • Your package management tools are misconfigured.
    • The file is not installed from any package. In such a case, no matching debuginfo package exists.

    Because further steps depend on this one, you must resolve this situation or abort this procedure. Describing the exact troubleshooting steps is beyond the scope of this procedure.

  3. Install the debuginfo packages by using the debuginfo-install utility. In the command, use the package name and other details you determined during the previous step: 

    # debuginfo-install zlib-1.2.11-10.el8.x86_64

Use the GNU Debugger (GDB) to diagnose application issues, control program execution, and inspect its internal state.

3.2.1. GNU debugger (GDB)
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Use the GNU Debugger (GDB) to inspect program execution and post-crash states. Also, you can analyze internal data and control execution flow when tracking down runtime errors. This command-line tool shows the detailed application state needed to identify and fix bugs in complex applications.

GDB capabilities

A single GDB session can debug the following types of programs:

  • Multithreaded and forking programs
  • Multiple programs at once
  • Programs on remote machines or in containers with the gdbserver utility connected over a TCP/IP network connection

Debugging requirements

To debug any executable code, GDB requires debugging information for that particular code:

  • For programs developed by you, you can create the debugging information while building the code.
  • For system programs installed from packages, you must install their debuginfo packages.

3.2.2. Attaching GDB to a process
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To examine a process, GDB must be attached to the process.

Prerequisites

  • GDB must be installed on the system

    Starting a program with GDB

  • When the program is not running as a process, start it with GDB: 

    $ gdb program

Replace program with a file name or path to the program.

GDB sets up to start execution of the program. You can set up breakpoints and the gdb environment before beginning the execution of the process with the run command.

Attaching GDB to an already-running process

To attach GDB to a program already running as a process:

  1. Find the process ID (pid) with the ps command: 

    $ ps -C program -o pid h

    Replace program with a file name or path to the program.

  2. Attach GDB to this process: 

    $ gdb -p pid

Replace pid with an actual process ID number from the ps output.

Attaching an already-running GDB to an already-running process

To attach an already running GDB to an already running program:

  1. Use the shell GDB command to run the ps command and find the program’s process ID (pid): 

    (gdb) shell ps -C program -o pid h

    Replace program with a file name or path to the program.

  2. Use the attach command to attach GDB to the program: 

    (gdb) attach pid

Replace pid by an actual process ID number from the ps output.

Note

In some cases, GDB might not be able to find the corresponding executable file. Use the file command to specify the path: 

(gdb) file path/to/program

3.2.3. Controlling program execution with GDB
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When the GDB debugger has been attached to a program, you can use several commands to control the execution of the program. These commands parse code, set breakpoints, and control program flow during debugging sessions.

Prerequisites

  • You must have the required debugging information available:

    • The program is compiled and built with debugging information, or
    • The relevant debuginfo packages are installed
  • GDB must be attached to the program to be debugged

GDB commands to step through the code

r (run)
Start the execution of the program. If run is executed with any arguments, those arguments are passed on to the executable as if the program has been started normally. Users normally issue this command after setting breakpoints.
start
Start the execution of the program but stop at the beginning of the program’s main function. If start is executed with any arguments, those arguments are passed on to the executable as if the program has been started normally.
c (continue)

Continue the execution of the program from the current state. The execution of the program will continue until one of the following becomes true:

  • A breakpoint is reached.
  • A specified condition is satisfied.
  • A signal is received by the program.
  • An error occurs.
  • The program terminates.
n (next)

Continue the execution of the program from the current state, until the next line of code in the current source file is reached. The execution of the program will continue until one of the following becomes true:

  • A breakpoint is reached.
  • A specified condition is satisfied.
  • A signal is received by the program.
  • An error occurs.
  • The program terminates.
s (step)
The step command also halts execution at each sequential line of code in the current source file. However, if the execution is currently stopped at a source line containing a function call, GDB stops the execution after entering the function call (rather than executing it).
until location
Continue the execution until the code location specified by the location option is reached.
fini (finish)

Resume the execution of the program and halt when execution returns from a function. The execution of the program will continue until one of the following becomes true:

  • A breakpoint is reached.
  • A specified condition is satisfied.
  • A signal is received by the program.
  • An error occurs.
  • The program terminates.
q (quit)
Terminate the execution and exit GDB.

3.2.4. Showing program internal values with GDB
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Displaying the values of a program’s internal variables is important for understanding of what the program is doing. The GNU Debugger (GDB) offers multiple commands that you can use to inspect the internal variables. The following are the most useful of these commands:

p (print)
Display the value of the argument given. Usually, the argument is the name of a variable of any complexity, from a simple single value to a structure. An argument can also be an expression valid in the current language, including the use of program variables and library functions, or functions defined in the program being tested.

It is possible to extend GDB with pretty-printer Python or Guile scripts for customized display of data structures (such as classes, structs) using the print command.

bt (backtrace)
Display the chain of function calls used to reach the current execution point, or the chain of functions used up until execution was terminated. This is useful for investigating serious bugs (such as segmentation faults) with elusive causes.

Adding the full option to the backtrace command displays local variables, too.

It is possible to extend GDB with frame filter Python scripts for customized display of data displayed using the bt and info frame commands. The term frame refers to the data associated with a single function call.

info
The info command is a generic command to provide information about various items. It takes an option specifying the item to describe.
  • The info args command displays options of the function call that is the currently selected frame.
  • The info locals command displays local variables in the currently selected frame.

For a list of the possible items, run the command help info in a GDB session:

+ 

(gdb) help info
l (list)
Show the line in the source code where the program stopped. This command is available only when the program execution is stopped. While not strictly a command to show internal state, list helps the user understand what changes to the internal state will happen in the next step of the program’s execution.

During a debugging session, you often need to investigate only specific sections of code. Breakpoints are markers that instruct GDB to stop the execution of a program at a defined location. Since breakpoints are typically associated with lines of source code, placing them requires you to specify the correct source file and line number.

  • To place a breakpoint:

    • Specify the name of the source code file and the line in that file: 

      (gdb) br file:line

    • When file is not present, name of the source file at the current point of execution is used: 

      (gdb) br line

    • Alternatively, use a function name to put the breakpoint on its start: 

      (gdb) br function_name

  • A program might encounter an error after a certain number of iterations of a task. To specify an additional condition to halt execution: 

    (gdb) br file:line if condition

Replace condition with a condition in the C or C++ language. The meaning of file and line is the same as above.

  • To inspect the status of all breakpoints and watchpoints: 

    (gdb) info br

  • To remove a breakpoint by using its number as displayed in the output of info br: 

    (gdb) delete number

  • To remove a breakpoint at a given location: 

    (gdb) clear file:line

GDB watchpoints pause execution when data changes or is accessed. Use them to debug unexpected variable corruption when the cause is unknown. Setting a watchpoint stops the program at the exact moment of access to inspect the state and find the root cause.

Using watchpoints in GDB

Watchpoints are markers which tell GDB to stop the execution of a program. Watchpoints are associated with data: placing a watchpoint requires specifying an expression that describes a variable, multiple variables, or a memory address.

  • To place a watchpoint for data change (write): 

    (gdb) watch expression

    Replace expression with an expression that describes what you want to watch. For variables, expression is equal to the name of the variable.

  • To place a watchpoint for data access (read): 

    (gdb) rwatch expression

  • To place a watchpoint for any data access (both read and write): 

    (gdb) awatch expression

  • To inspect the status of all watchpoints and breakpoints: 

    (gdb) info br

  • To remove a watchpoint: 

    (gdb) delete num

    Replace the num option with the number reported by the info br command.

Some programs use forking or threads to achieve parallel code execution. To debug multiple simultaneous execution paths, you can use a variety of commands based on your use case.

Prerequisites

  • You must understand the concepts of process forking and threads.

    Debugging forked programs with GDB
    Forking is a situation when a program (parent) creates an independent copy of itself (child). Use the following settings and commands to affect what GDB does when a fork occurs:

  • The follow-fork-mode setting controls whether GDB follows the parent or the child after the fork.

    set follow-fork-mode parent
    After a fork, debug the parent process. This is the default.
    set follow-fork-mode child
    After a fork, debug the child process.
    show follow-fork-mode
    Display the current setting of follow-fork-mode.

  • The set detach-on-fork setting controls whether the GDB keeps control of the other (not followed) process or leaves it to run.

    set detach-on-fork on
    The process which is not followed (depending on the value of follow-fork-mode) is detached and runs independently. This is the default.
    set detach-on-fork off
    GDB keeps control of both processes. The process which is followed (depending on the value of follow-fork-mode) is debugged as usual, while the other is suspended.
    show detach-on-fork
    Display the current setting of detach-on-fork.
Debugging threaded programs with GDB
GDB has the ability to debug individual threads, and to manipulate and examine them independently. To make GDB stop only the thread that is examined, use the commands set non-stop on and set target-async on. You can add these commands to the .gdbinit file. After that functionality is turned on, GDB is ready to conduct thread debugging.

GDB uses a concept of current thread. By default, commands apply to the current thread only.

info threads
Display a list of threads with their id and gid numbers, indicating the current thread.
thread id
Set the thread with the specified id as the current thread.
thread apply ids command
Apply the command command to all threads listed by ids. The ids option is a space-separated list of thread ids. A special value all applies the command to all threads.
break location thread id if condition
Set a breakpoint at a certain location with a certain condition only for the thread number id.
watch expression thread id
Set a watchpoint defined by expression only for the thread number id.
command&
Execute command command and return immediately to the gdb prompt (gdb), continuing any code execution in the background.
interrupt
Halt execution in the background.

3.3. Recording Application Interactions
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The executable code of applications interacts with the code of the operating system and shared libraries. Recording an activity log of these interactions can provide enough insight into the application’s behavior without debugging the actual application code. Alternatively, analyzing an application’s interactions can help pinpoint the conditions in which a bug manifests.

To record application interactions, you can use several tools are available in RHEL. For system calls use strace, for library calls use ltrace, and for advanced probing SystemTap. Select the appropriate tool to log specific runtime behaviors and diagnose integration issues.

strace

The strace tool primarily enables logging of system calls (kernel functions) used by an application.

  • The strace tool can provide a detailed output about calls, because strace interprets parameters and results with knowledge of the underlying kernel code. Numbers are turned into the corresponding constant names, bitwise combined flags expanded to flag list, pointers to character arrays dereferenced to provide the actual string, and more. Support for more recent kernel features may be lacking.
  • You can filter the traced calls to reduce the amount of captured data.
  • The use of strace does not require any particular setup except for setting up the log filter.
  • Tracing the application code with strace results in significant slowdown of the application’s execution. As a result, strace is not suitable for many production deployments. As an alternative, consider using ltrace or SystemTap.
  • The version of strace available in Red Hat Developer Toolset can also perform system call tampering. This capability is useful for debugging.
ltrace
The ltrace tool enables logging of an application’s user space calls into shared objects (dynamic libraries).
  • The ltrace tool enables tracing calls to any library.
  • You can filter the traced calls to reduce the amount of captured data.
  • The use of ltrace does not require any particular setup except for setting up the log filter.
  • The ltrace tool is lightweight and fast, offering an alternative to strace: it is possible to trace the corresponding interfaces in libraries such as glibc with ltrace instead of tracing kernel functions with strace.
  • Because ltrace does not handle a known set of calls such as strace, it does not attempt to explain the values passed to library functions. The ltrace output contains only raw numbers and pointers. The interpretation of ltrace output requires consulting the actual interface declarations of the libraries present in the output.
Note

In Red Hat Enterprise Linux 9, a known issue prevents ltrace from tracing system executable files. This limitation does not apply to executable files built by users.

SystemTap

SystemTap is an instrumentation platform for probing running processes and kernel activity on the Linux system. SystemTap uses its own scripting language for programming custom event handlers.

  • Compared to using strace and ltrace, scripting the logging means more work in the initial setup phase. However, the scripting capabilities extend SystemTap’s usefulness beyond just producing logs.
  • SystemTap works by creating and inserting a kernel module. The use of SystemTap is efficient and does not create a significant slowdown of the system or application execution on its own.
  • SystemTap includes a set of usage examples.
GDB

The GNU Debugger (GDB) is primarily meant for debugging, not logging. However, some of its features make it useful even in the scenario where an application’s interaction is the primary activity of interest.

  • With GDB, it is possible to conveniently combine the capture of an interaction event with immediate debugging of the subsequent execution path.
  • GDB is best suited for analyzing response to infrequent or singular events, after the initial identification of problematic situation by other tools. Using GDB in any scenario with frequent events becomes inefficient or even impossible.

Additional resources

To monitor the system (kernel) calls performed by an application, use the strace tool.

Prerequisites

  • You must have strace installed on the system.

Procedure

  1. Identify the system calls to monitor.

  2. Start strace and attach it to the program.

    • If the program you want to monitor is not running, start strace and specify the program: 

      $ strace -fvttTyy -s 256 -e trace=call program

    • If the program is already running, find its process id (pid) and attach strace to it:

      1. Find the process ID: 

        $ ps -C program
         
        (...)

      2. Attach strace to the process: 

        $ strace -fvttTyy -s 256 -e trace=call -ppid
    • Replace call with the system calls to be displayed. You can use the -e trace=call option multiple times. If left out, strace will display all system call types. See the strace(1) manual page for more information.
    • If you do not want to trace any forked processes or threads, omit the -f option.

  3. The strace tool displays the system calls made by the application and their details.

    In most cases, an application and its libraries make a large number of calls and strace output displays immediately, if no filter for system calls is set.

  4. The strace tool exits when the program exits.

    To terminate the monitoring before the traced program exits, press Ctrl+C.

    • If strace started the program, the program terminates together with strace.
    • If you attached strace to an already running program, the program terminates together with strace.

  5. Analyze the list of system calls done by the application.

    • Problems with resource access or availability are present in the log as calls returning errors.
    • Values passed to the system calls and patterns of call sequences provide insight into the causes of the application’s behaviour.
    • If the application crashes, the important information is probably at the end of log.
    • The output contains unnecessary information. However, you can construct a more precise filter for the system calls of interest and repeat the procedure.
Note

It is advantageous to both see the output and save it to a file. Use the tee command to achieve this: 

$ strace ... |& tee your_log_file.log

To monitor an application’s calls to functions available in libraries (shared objects), use the ltrace tool.

Note

In Red Hat Enterprise Linux 9, a known issue prevents ltrace from tracing system executable files. This limitation does not apply to executable files built by users.

Prerequisites

  • You must have ltrace installed on the system.

Procedure

  1. Identify the libraries and functions of interest, if possible.

  2. Start ltrace and attach it to the program.

    • If the program you want to monitor is not running, start ltrace and specify program: 

      $ ltrace -f -l library -e function program
    • If the program is already running, find its process id (pid) and attach ltrace to it:

  3. Find the process ID: 

    $ ps -C program
     
    (...)

  4. Attach ltrace to the process: 

    $ ltrace -f -l library -e function -ppid program

    • Use the -e, -f and -l options to filter the output:

      • Supply the function names to be displayed as function. The -e function option can be used multiple times. If left out, ltrace displays calls to all functions.
      • Instead of specifying functions, you can specify whole libraries with the -l library option. This option behaves similarly to the -e function option.
      • If you do not want to trace any forked processes or threads, omit the -f option.

      See the ltrace(1)_ manual page for more information.

  5. ltrace displays the library calls made by the application.

    In most cases, an application makes a large number of calls and ltrace output displays immediately, if no filter is set.

  6. ltrace exits when the program exits.

    To terminate the monitoring before the traced program exits, press ctrl+C.

    • If ltrace started the program, the program terminates together with ltrace.
    • If you attached ltrace to an already running program, the program terminates together with ltrace.

  7. Analyze the list of library calls done by the application.

    • If the application crashes, the important information is probably at the end of log.
    • The output contains unnecessary information. However, you can construct a more precise filter and repeat the procedure.
Note

It is advantageous to both see the output and save it to a file. Use the tee command to achieve this: 

$ ltrace ... |& tee your_log_file.log

To register custom event handlers for kernel events, use the SystemTap tool. SystemTap is more efficient than the strace tool, but requires more setup. The included strace.stp script provides strace-like functionality. Installing SystemTap also installs the strace.stp script, which provides an approximation of the strace functionality when using SystemTap.

Prerequisites

  • SystemTap and the corresponding kernel packages must be installed on the system.

Procedure

  1. Find the process ID (pid) of the process you want to monitor: 

    $ ps -aux

  2. Run SystemTap with the strace.stp script: 

    # stap /usr/share/systemtap/examples/process/strace.stp -x pid

    The value of pid is the process id.

    The script is compiled to a kernel module, which is then loaded. This introduces a slight delay between entering the command and getting the output.

  3. When the process performs a system call, the call name and its parameters are printed to the terminal.
  4. The script exits when the process terminates, or when you press Ctrl+C.

To stop program execution when the program performs specific system calls, use GDB catchpoints, then inspect the program state and system call parameters at those points.

Prerequisites

  • You must understand the usage of GDB breakpoints.
  • GDB must be attached to the program.

Procedure

  1. Set the catchpoint: 

    (gdb) catch syscall syscall-name

    The command catch syscall sets a special type of breakpoint that halts execution when the program performs a system call.

    The syscall-name option specifies the name of the call. You can specify multiple catchpoints for various system calls. Leaving out the syscall-name option causes GDB to stop on any system call.

  2. Start execution of the program.

    • If the program has not started execution, start it: 

      (gdb) r

    • If the program execution is halted, resume it: 

      (gdb) c
  3. GDB halts execution after the program performs any specified system call.

Additional resources

To stop the execution of a program under specific circumstances, you can use the GNU Debugger (GDB). To stop the execution when the program receives a signal from the operating system, use a GDB catchpoint.

Prerequisites

  • You must understand the usage of GDB breakpoints.
  • GDB must be attached to the program.

Procedure

  1. Set the catchpoint: 

    (gdb) catch signal signal-type

    The command catch signal sets a special type of a breakpoint that halts execution when a signal is received by the program. The signal-type option specifies the type of the signal. Use the special value 'all' to catch all signals.

  2. Let the program run.

    • If the program has not started execution, start it: 

      (gdb) r

    • If the program execution is halted, resume it: 

      (gdb) c
  3. GDB halts execution after the program receives any specified signal.

3.4. Debugging a Crashed Application
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Sometimes, it is not possible to debug an application directly. In these situations, you can collect information about the application at the moment of its termination and analyze it afterwards.

A core dump records parts of an application’s memory when the application stops. After an application fails, you can analyze the core dump, along with the executable and debuginfo, by using a debugger.

The Linux operating system kernel can record core dumps automatically, if this functionality is enabled. Alternatively, you can send a signal to any running application to generate a core dump regardless of its actual state.

Warning

Some limits might affect the ability to generate a core dump. To see the current limits: 

$ ulimit -a

To record application crashes, set up core dump saving and add information about the system.

Procedure

  1. To enable core dumps, ensure that the /etc/systemd/system.conf file contains the following lines: 

    DumpCore=yes
DefaultLimitCORE=infinity

    You can also add comments describing if these settings were previously present, and what the previous values were. This will enable you to reverse these changes later, if needed. Comments are lines starting with the # character.

    Changing the file requires administrator level access.

  2. Apply the new configuration: 

    # systemctl daemon-reexec

  3. Remove the limits for core dump sizes: 

    $ ulimit -c unlimited

    To reverse this change, run the command with value 0 instead of unlimited.

  4. Install the sos package which provides the sosreport utility for collecting system information: 

    # dnf install sos
  5. When an application crashes, a core dump is generated and handled by systemd-coredump.

  6. Create an SOS report to provide additional information about the system: 

    # sosreport

    This creates a .tar archive containing information about your system, such as copies of configuration files.

  7. Locate the core dump: 

    $ coredumpctl list executable-name

  8. Export the core dump: 

    $ coredumpctl dump executable-name > /path/to/file-for-export

    If the application crashed multiple times, output of the first command lists more captured core dumps. In that case, construct for the second command a more precise query by using the other information. See the coredumpctl(1) manual page for details.

  9. Transfer the core dump and the SOS report to the computer where the debugging will take place. Transfer the executable file, too, if it is known.

    Important

    When the executable file is not known, subsequent analysis of the core file identifies it.

  10. Optional: Remove the core dump and SOS report after transferring them, to free up disk space.

To inspect the state of an application at the moment it terminated unexpectedly, use core dumps.

Prerequisites

  • You must have a core dump file and sosreport from the system where the crash occurred.
  • GDB and elfutils must be installed on your system.

Procedure

  1. To identify the executable file where the crash occurred, run the eu-unstrip command with the core dump file: 

    $ eu-unstrip -n --core=./core.9814
     
    0x400000+0x207000 2818b2009547f780a5639c904cded443e564973e@0x400284 /usr/bin/sleep /usr/lib/debug/bin/sleep.debug [exe]
0x7fff26fff000+0x1000 1e2a683b7d877576970e4275d41a6aaec280795e@0x7fff26fff340 . - linux-vdso.so.1
0x35e7e00000+0x3b6000 374add1ead31ccb449779bc7ee7877de3377e5ad@0x35e7e00280 /usr/lib64/libc-2.14.90.so /usr/lib/debug/lib64/libc-2.14.90.so.debug libc.so.6
0x35e7a00000+0x224000 3ed9e61c2b7e707ce244816335776afa2ad0307d@0x35e7a001d8 /usr/lib64/ld-2.14.90.so /usr/lib/debug/lib64/ld-2.14.90.so.debug ld-linux-x86-64.so.2

    The output contains details for each module on a line, separated by spaces. The information is listed in this order:

    1. The memory address where the module was mapped
    2. The build-id of the module and where in the memory it was found
    3. The module’s executable file name, displayed as - when unknown, or as . when the module has not been loaded from a file
    4. The source of debugging information, displayed as a file name when available, as . when contained in the executable file itself, or as - when not present at all
    5. The shared library name (soname) or [exe] for the main module

    In this example, the important details are the file name /usr/bin/sleep and the build-id 2818b2009547f780a5639c904cded443e564973e on the line containing the text [exe]. With this information, you can identify the executable file required for analyzing the core dump.

  2. Get the executable file that crashed.

    • If possible, copy it from the system where the crash occurred. Use the file name extracted from the core file.

    • You can also use an identical executable file on your system. Each executable file built on Red Hat Enterprise Linux contains a note with a unique build-id value. Determine the build-id of the relevant locally available executable files: 

      $ eu-readelf -n executable_file

      Use this information to match the executable file on the remote system with your local copy. The build-id of the local file and build-id listed in the core dump must match.

    • Finally, if the application is installed from an RPM package, you can get the executable file from the package. Use the sosreport output to find the exact version of the package required.
  3. Get the shared libraries used by the executable file. Use the same steps as for the executable file.
  4. If the application is distributed as a package, load the executable file in GDB, to display hints for missing debuginfo packages. For more details, see Section 3.1.4, “Getting debuginfo packages for an application or library using GDB”.

  5. To examine the core file in detail, load the executable file and core dump file with GDB: 

    $ gdb -e executable_file -c core_file

    Further messages about missing files and debugging information help you identify what is missing for the debugging session. Return to the previous step if needed.

    If the application’s debugging information is available as a file instead of as a package, load this file in GDB with the symbol-file command: 

    (gdb) symbol-file program.debug

    Replace program.debug with the actual file name.

    Note

    It might not be necessary to install the debugging information for all executable files contained in the core dump. Most of these executable files are libraries used by the application code. These libraries might not directly contribute to the problem you are analyzing, and you do not need to include debugging information for them.

  6. Use the GDB commands to inspect the state of the application at the moment it crashed. See Inspecting Application Internal State with GDB.

    Note

    When analyzing a core file, GDB is not attached to a running process. Commands for controlling execution have no effect.

Additional resources

To manage and analyze core dumps directly on the affected system, use coredumpctl. This tool simplifies finding, capturing, and inspecting crash data. Identify an unresponsive process, force a core dump, and verify its successful capture to diagnose application failures.

Prerequisites

  • The system must be configured to use systemd-coredump for core dump handling. To verify this is true: 

    $ sysctl kernel.core_pattern

    The configuration is correct if the output starts with the following: 

    kernel.core_pattern = |/usr/lib/systemd/systemd-coredump

Procedure

  1. Find the PID of the hung process, based on a known part of the executable file name: 

    $ pgrep -a executable-name-fragment

    This command will output a line in the form 

    PID command-line

    Use the command-line value to verify that the PID belongs to the intended process.

    For example: 

    $ pgrep -a bc
     
    5459 bc

  2. Send an abort signal to the process: 

    # kill -ABRT PID

  3. Verify that the core has been captured by coredumpctl: 

    $ coredumpctl list PID

    For example: 

    $ coredumpctl list 5459
     
    TIME                            PID   UID   GID SIG COREFILE  EXE
Thu 2019-11-07 15:14:46 CET    5459  1000  1000   6 present   /usr/bin/bc

  4. Further examine or use the core file as needed.

    You can specify the core dump by PID and other values. See the coredumpctl(1) manual page for further details.

    • To show details of the core file: 

      $ coredumpctl info PID

    • To load the core file in the GDB debugger: 

      $ coredumpctl debug PID

      Depending on availability of debugging information, GDB will suggest commands to run, such as: 

      Missing separate debuginfos, use: dnf debuginfo-install bc-1.07.1-5.el8.x86_64

      For more details on this process, see Getting debuginfo packages for an application or library using GDB.

    • To export the core file for further processing elsewhere: 

      $ coredumpctl dump PID > /path/to/file_for_export

      Replace /path/to/file_for_export with the file where you want to put the core dump.

3.4.5. Dumping process memory with gcore
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To capture the memory state of a running process without terminating it, use the gcore utility. This creates a core dump file for offline analysis. The result is a snapshot of the application’s memory that helps you investigate issues while the service remains available.

Prerequisites

  • You must understand what core dumps are and how they are created.
  • GDB must be installed on the system.

Procedure

  1. Find out the process id (pid). Use tools such as ps, pgrep, and top: 

    $ ps -C some-program

  2. Dump the memory of this process: 

    $ gcore -o filename pid

    This creates a file filename and dumps the process memory in it. While the memory is being dumped, the execution of the process is halted.

  3. After the core dump is finished, the process resumes normal execution.

  4. Create an SOS report to provide additional information about the system: 

    # sosreport

    This creates a tar archive containing information about your system, such as copies of configuration files.

  5. Transfer the program’s executable file, core dump, and the SOS report to the computer where the debugging will take place.
  6. Optional: Remove the core dump and SOS report after transferring them, to free up disk space.

3.4.6. Dumping protected process memory with GDB
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To dump protected process memory, configure the GNU Debugger (GDB) to ignore core dump filters. Capture memory regions flagged as non-dumpable, such as those conserving resources or holding sensitive data. Use the gcore command within GDB to generate the complete core file.

Prerequisites

  • You must understand what core dumps are.
  • GDB must be installed on the system.
  • GDB must be already attached to the process with protected memory.

Procedure

  1. Set GDB to ignore the settings in the /proc/PID/coredump_filter file: 

    (gdb) set use-coredump-filter off

  2. Set GDB to ignore the memory page flag VM_DONTDUMP: 

    (gdb) set dump-excluded-mappings on

  3. Dump the memory: 

    (gdb) gcore core-file

    Replace core-file with name of file where you want to dump the memory.

3.5. Compatibility breaking changes in GDB
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The version of the GNU Debugger (GDB) provided in Red Hat Enterprise Linux 9 contains several changes that break compatibility.

Commands
  • The gdb -P python-script.py command is no longer supported.

Use the gdb -ex 'source python-script.py' command instead.

  • The gdb COREFILE command is no longer supported.

    Use the gdb EXECUTABLE --core COREFILE command instead to load the executable specified in the core file.

  • GDB now styles output by default.

    This new change might break scripts that try to parse the output of GDB. Use the gdb -ex 'set style enabled off' command to disable styling in scripts.

  • Commands now define syntax for symbols according to the language.

    The info functions, info types, info variables and rbreak commands now define the syntax for entities according to the language chosen by the set language command. By setting it to set language auto means that GDB will automatically choose the language of the shown entities.

  • The set print raw frame-arguments and show print raw frame-arguments commands have been deprecated.

    These commands are replaced with the set print raw-frame-arguments and show print raw-frame-arguments commands. The old commands may be removed in future versions.

  • The following TUI commands are now case-sensitive:

    • focus
    • winheight
    • +
    • -
    • >
    • <

  • The help and apropos commands now display command information only once.

    These commands now show the documentation of a command only once, even if that command has one or more aliases. These commands now show the command name, then all of its aliases, and finally the description of the command.

MI interpreter
  • The default version of the MI interpreter is now 3.

The output of information about multi-location breakpoints (which is syntactically incorrect in MI 2) has changed in MI 3. This affects the following commands and events:

  • -break-insert
  • -break-info
  • =breakpoint-created
  • =breakpoint-modified

Use the -fix-multi-location-breakpoint-output command to enable this behavior with previous MI versions.

Python API

  • The following symbols are now deprecated:

    • gdb.SYMBOL_VARIABLES_DOMAIN
    • gdb.SYMBOL_FUNCTIONS_DOMAIN
    • gdb.SYMBOL_TYPES_DOMAIN
  • The gdb.Value type has a new constructor, which is used to construct a gdb.Value from a Python buffer object and a gdb.Type.
  • The frame information printed by the Python frame filtering code is now consistent with what the backtrace command prints when there are no filters, or when using the backtrace command’s -no-filters option.

3.6. Debugging applications in containers
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To troubleshoot container applications, you can use various command-line tools.

Note

This is not a complete list of command-line tools. The choice of tool for debugging a container application is heavily based on the container image and your use case.

For instance, the systemctl, journalctl, ip, netstat, ping, traceroute, perf, iostat tools may need root access because they interact with system-level resources such as networking, systemd services, or hardware performance counters, which are restricted in rootless containers for security reasons.

Rootless containers operate without requiring elevated privileges, running as non-root users within user namespaces to provide improved security and isolation from the host system. They offer limited interaction with the host, reduced attack surface, and enhanced security by mitigating the risk of privilege escalation vulnerabilities.

Rootful containers run with elevated privileges, typically as the root user, granting full access to system resources and capabilities. While rootful containers offer greater flexibility and control, they pose security risks due to their potential for privilege escalation and exposure of the host system to vulnerabilities.

For more information about rootful and rootless containers, see Setting up rootless containers, Upgrading to rootless containers, and Special considerations for rootless containers.

Systemd and process management tools, systemctl
Controls systemd services within containers, allowing start, stop, enable, and disable operations.
journalctl
Views logs generated by systemd services, aiding in troubleshooting container issues.
Networking tools, ip
Manages network interfaces, routing, and addresses within containers.
netstat
Displays network connections, routing tables, and interface statistics.
ping
Verifies network connectivity between containers or hosts.
traceroute
Identifies the path packets take to reach a destination, useful for diagnosing network issues.
Process and performance tools, ps
Lists currently running processes within containers.
top
Provides real-time insights into resource usage by processes within containers.
htop
Interactive process viewer for monitoring resource utilization.
perf
CPU performance profiling, tracing, and monitoring, aiding in pinpointing performance bottlenecks within the system or applications.
vmstat
Reports virtual memory statistics within containers, aiding in performance analysis.
iostat
Monitors input/output statistics for block devices within containers.
gdb (GNU Debugger)
A command-line debugger that helps in examining and debugging programs by allowing users to track and control their execution, inspect variables, and analyze memory and registers during runtime. For more information, see the Debugging applications within Red Hat OpenShift containers article.
strace
Intercepts and records system calls made by a program, aiding in troubleshooting by revealing interactions between the program and the operating system.
Security and access control tools, sudo
Enables executing commands with elevated privileges.
chroot
Changes the root directory for a command, helpful in testing or troubleshooting within a different root directory.
Podman-specific tools, podman logs
Batch-retrieves whatever logs are present for one or more containers at the time of execution.
podman inspect
Displays the low-level information on containers and images as identified by name or ID.
podman events
Monitor and print events that occur in Podman. Each event includes a timestamp, a type, a status, a name (if applicable), and an image (if applicable). The default logging mechanism is journald.
podman run --health-cmd
Use the health check to determine the health or readiness of the process running inside the container.
podman top
Display the running processes of the container.
podman exec
Running commands in or attaching to a running container is extremely useful to get a better understanding of what is happening in the container.
podman export
When the container fails, it is basically impossible to know what happened. Exporting the filesystem structure from the container will allow for checking other logs files that may not be in the mounted volumes.

Chapter 4. Additional toolsets for development
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GCC Toolset and related toolsets provide newer compilers and debuggers. Install, use, and run container images for development.

4.1. Using the GCC Toolset
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4.1.1. What is the GCC Toolset
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Red Hat Enterprise Linux 9 continues support for the GCC Toolset, a compiler toolset that provides a variety of development and performance analysis tools. GCC Toolset is similar to Red Hat Developer Toolset.

GCC Toolset is available as an Application Stream in the form of a software collection in the AppStream repository. GCC Toolset is fully supported under Red Hat Enterprise Linux Subscription Level Agreements, is functionally complete, and is intended for production use. Applications and libraries provided by the GCC Toolset do not replace the Red Hat Enterprise Linux system versions, do not override them, and do not automatically become default or preferred choices. Using a framework called software collections, an additional set of developer tools is installed into the /opt/ directory and is explicitly enabled by the user on-demand by using the scl utility. Unless noted otherwise for specific tools or features, the GCC Toolset is available for all architectures supported by Red Hat Enterprise Linux.

For information about the length of support, see Red Hat Enterprise Linux Application Streams Life Cycle.

4.1.2. Installing the GCC Toolset
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Installing the GCC Toolset on a system installs the main tools and all necessary dependencies. Note that some parts of the toolset are not installed by default and must be installed separately.

Procedure

  • To install the GCC Toolset version N: 

    # dnf install gcc-toolset-N

To install only certain tools from the GCC Toolset instead of the whole toolset, list the available packages and install the selected ones with the dnf package management tool. Use selective installation to access packages not installed by default with the full toolset.

Procedure

  1. List the packages available in the GCC Toolset version N: 

    $ dnf list available gcc-toolset-N-\*

  2. To install any of these packages: 

    # dnf install package_name

    Replace package_name with a space-separated list of packages to install. For example, to install the gcc-toolset-13-annobin-annocheck and gcc-toolset-13-binutils-devel packages: 

    # dnf install gcc-toolset-13-annobin-annocheck gcc-toolset-13-binutils-devel

4.1.4. Uninstalling the GCC Toolset
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To remove the GCC Toolset from your system, uninstall it by using the dnf package management tool.

Procedure

  • To uninstall the GCC Toolset version N: 

    # dnf remove gcc-toolset-N\*

4.1.5. Accessing the GCC Toolset
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To access the GCC Toolset, you can run a specific tool using the scl utility, or start a shell session where the toolset versions override the system versions.

Procedure

  • To run a single tool from the GCC Toolset version N: 

    $ scl enable gcc-toolset-N tool

    Replace tool with the command provided by the tool you want to run.

  • To run a shell session where tool versions from the GCC Toolset version N override system versions of these tools: 

    $ scl enable gcc-toolset-N bash

4.2. GCC Toolset 12
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Learn about information specific to the GCC Toolset version 12 and the tools contained in this version.

GCC Toolset 12 provides the following tools and versions.

Expand
Table 4.1. Tool versions in the GCC Toolset 12
NameVersionDescription

GCC

12.2.1

A portable compiler suite with support for C, C++, and Fortran.

GDB

11.2

A command-line debugger for programs written in C, C++, and Fortran.

binutils

2.38

A collection of binary tools and other utilities to inspect and manipulate object files and binaries.

dwz

0.14

A tool to optimize DWARF debugging information contained in ELF shared libraries and ELF executables for size.

annobin

11.08

A build security checking tool.

4.2.2. C++ compatibility in the GCC Toolset 12
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The GNU Compiler Collection (GCC) in the GCC Toolset can use the following C++ standards:

Important

The compatibility information presented here apply only to the GCC from the GCC Toolset 12.

C++14

This language standard is available in the GCC Toolset 12.

Using the C++14 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 6 or later.

C++11

This language standard is available in the GCC Toolset 12.

Using the C++11 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 5 or later.

C++98
This language standard is available in the GCC Toolset 12. Binaries, shared libraries and objects built using this standard can be freely mixed regardless of being built with GCC from the GCC Toolset, Red Hat Developer Toolset, and RHEL 5, 6, 7 and 8.
C++17

This language standard is available in the GCC Toolset 12.

This is the default language standard setting for the GCC Toolset 12, with GNU extensions, equivalent to explicitly using option -std=gnu++17.

Using the C++17 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 10 or later.

C++20 and C++23

This language standard is available in the GCC Toolset 12 only as an experimental, unstable, and unsupported capability. Additionally, compatibility of objects, binary files, and libraries built using this standard cannot be guaranteed.

To enable C++20 support, add the command-line option -std=c++20 to your g++ command line.

To enable C++23 support, add the command-line option -std=c++23 to your g++ command line.

All of the language standards are available in both the standard compliant variant or with GNU extensions.

When mixing objects built by using the GCC Toolset with those built with the RHEL toolchain (particularly .o or .a files), the GCC Toolset toolchain should be used for any linkage. This ensures any newer library features provided only by the GCC Toolset are resolved at link time.

4.2.3. Specifics of GCC in the GCC Toolset 12
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Certain behaviors and requirements of the GCC Toolset 12 differ from the base Red Hat Enterprise Linux GNU Compiler Collection (GCC). These include automatic static linking of certain library features and the requirement to specify libraries after object files during linking.

Static linking of libraries

Certain more recent library features are statically linked into applications built with the GCC Toolset to support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a security erratum.

Important

Because of this additional security risk, developers are strongly advised not to statically link their entire application for the same reasons.

Specify libraries after object files when linking

In the GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux. However, the linker scripts use the names of the corresponding shared object files. As a consequence, the linker uses different symbol handling rules than expected, and does not recognize symbols required by object files when the option adding the library is specified before options specifying the object files: 

$ scl enable gcc-toolset-12 'gcc -lsomelib objfile.o'

Using a library from the GCC Toolset in this manner results in the linker error message undefined reference to symbol. To prevent this problem, follow the standard linking practice and specify the option adding the library after the options specifying the object files: 

$ scl enable gcc-toolset-12 'gcc objfile.o -lsomelib'

Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of GCC.

4.2.4. Specifics of binutils in the GCC Toolset 12
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Certain behaviors and requirements of binutils in the GCC Toolset 12 differ from the base Red Hat Enterprise Linux binutils. These include automatic static linking of certain library features and the requirement to specify libraries after object files during linking.

Static linking of libraries

Certain more recent library features are statically linked into applications built with the GCC Toolset to support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a security erratum.

Important

Because of this additional security risk, developers are strongly advised not to statically link their entire application for the same reasons.

Specify libraries after object files when linking

In the GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux. However, the linker scripts use the names of the corresponding shared object files. As a consequence, the linker uses different symbol handling rules than expected, and does not recognize symbols required by object files when the option adding the library is specified before options specifying the object files: 

$ scl enable gcc-toolset-12 'ld -lsomelib objfile.o'

Using a library from the GCC Toolset in this manner results in the linker error message undefined reference to symbol. To prevent this problem, follow the standard linking practice, and specify the option adding the library after the options specifying the object files: 

$ scl enable gcc-toolset-12 'ld objfile.o -lsomelib'

Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of binutils.

4.2.5. Specifics of annobin in the GCC Toolset 12
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Under some circumstances, due to a synchronization issue between annobin and gcc in the GCC Toolset 12, your compilation can fail with an error message that looks similar to the following: 

cc1: fatal error: inaccessible plugin file
opt/rh/gcc-toolset-12/root/usr/lib/gcc/architecture-linux-gnu/12/plugin/gcc-annobin.so
expanded from short plugin name gcc-annobin: No such file or directory

To work around the problem, create a symbolic link in the plugin directory from the annobin.so file to the gcc-annobin.so file:

  1. Change to the plugin directory: 

    # cd /opt/rh/gcc-toolset-12/root/usr/lib/gcc/architecture-linux-gnu/12/plugin

  2. Create the symbolic link: 

    # ln -s annobin.so gcc-annobin.so

Replace architecture with the architecture you use in your system:

  • aarch64
  • i686
  • ppc64le
  • s390x
  • x86_64

4.3. GCC Toolset 13
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Learn about information specific to the GCC Toolset version 13 and the tools contained in this version.

GCC Toolset 13 provides the following tools and versions.

Expand
Table 4.2. Tool versions in the GCC Toolset 13
NameVersionDescription

GCC

13.2.1

A portable compiler suite with support for C, C++, and Fortran.

GDB

12.1

A command-line debugger for programs written in C, C++, and Fortran.

binutils

2.40

A collection of binary tools and other utilities to inspect and manipulate object files and binaries.

dwz

0.14

A tool to optimize DWARF debugging information contained in ELF shared libraries and ELF executables for size.

annobin

12.32

A build security checking tool.

4.3.2. C++ compatibility in the GCC Toolset 13
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The GNU Compiler Collection (GCC) compiler in the GCC Toolset can use the following C++ standards:

Important

The compatibility information presented here apply only to the GCC from the GCC Toolset 13.

C++14

This language standard is available in the GCC Toolset 13.

Using the C++14 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 6 or later.

C++11

This language standard is available in the GCC Toolset 13.

Using the C++11 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 5 or later.

C++98
This language standard is available in the GCC Toolset 13. Binaries, shared libraries and objects built using this standard can be freely mixed regardless of being built with GCC from the GCC Toolset, Red Hat Developer Toolset, and RHEL 5, 6, 7 and 8.
C++17

This language standard is available in the GCC Toolset 13.

This is the default language standard setting for the GCC Toolset 13, with GNU extensions, equivalent to explicitly using option -std=gnu++17.

Using the C++17 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 10 or later.

C++20 and C++23

These language standards are available in the GCC Toolset 13 only as an experimental, unstable, and unsupported capability. Additionally, compatibility of objects, binary files, and libraries built using this standard cannot be guaranteed.

To enable the C++20 standard, add the command-line option -std=c++20 to your g++ command line.

To enable the C++23 standard, add the command-line option -std=c++23 to your g++ command line.

All of the language standards are available in both the standard compliant variant or with GNU extensions.

When mixing objects built by using the GCC Toolset with those built with the RHEL toolchain (particularly .o or .a files), the GCC Toolset toolchain should be used for any linkage. This ensures any newer library features provided only by the GCC Toolset are resolved at link time.

4.3.3. Specifics of GCC in the GCC Toolset 13
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Certain behaviors and requirements of the GCC Toolset 13 differ from the base Red Hat Enterprise Linux GNU Compiler Collection (GCC). These include automatic static linking of certain library features and the requirement to specify libraries after object files during linking.

Static linking of libraries

Certain more recent library features are statically linked into applications built with the GCC Toolset to support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a security erratum.

Important

Because of this additional security risk, developers are strongly advised not to statically link their entire application for the same reasons.

Specify libraries after object files when linking

In the GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux. However, the linker scripts use the names of the corresponding shared object files. As a consequence, the linker uses different symbol handling rules than expected, and does not recognize symbols required by object files when the option adding the library is specified before options specifying the object files: 

$ scl enable gcc-toolset-13 'gcc -lsomelib objfile.o'

Using a library from the GCC Toolset in this manner results in the linker error message undefined reference to symbol. To prevent this problem, follow the standard linking practice and specify the option adding the library after the options specifying the object files: 

$ scl enable gcc-toolset-13 'gcc objfile.o -lsomelib'

Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of GCC.

4.3.4. Specifics of binutils in the GCC Toolset 13
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Certain behaviors and requirements of binutils in the GCC Toolset 13 differ from the base Red Hat Enterprise Linux binutils. These include automatic static linking of certain library features and the requirement to specify libraries after object files during linking.

Static linking of libraries

Certain more recent library features are statically linked into applications built with the GCC Toolset to support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a security erratum.

Important

Because of this additional security risk, developers are strongly advised not to statically link their entire application for the same reasons.

Specify libraries after object files when linking

In the GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux. However, the linker scripts use the names of the corresponding shared object files. As a consequence, the linker uses different symbol handling rules than expected, and does not recognize symbols required by object files when the option adding the library is specified before options specifying the object files: 

$ scl enable gcc-toolset-13 'ld -lsomelib objfile.o'

Using a library from the GCC Toolset in this manner results in the linker error message undefined reference to symbol. To prevent this problem, follow the standard linking practice, and specify the option adding the library after the options specifying the object files: 

$ scl enable gcc-toolset-13 'ld objfile.o -lsomelib'

Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of binutils.

4.3.5. Specifics of annobin in the GCC Toolset 13
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Under some circumstances, due to a synchronization issue between annobin and gcc in the GCC Toolset 13, your compilation can fail with an error message that looks similar to the following: 

cc1: fatal error: inaccessible plugin file
opt/rh/gcc-toolset-13/root/usr/lib/gcc/architecture-linux-gnu/13/plugin/gcc-annobin.so
expanded from short plugin name gcc-annobin: No such file or directory

To work around the problem, create a symbolic link in the plugin directory from the annobin.so file to the gcc-annobin.so file:

  1. Change to the plugin directory: 

    # cd /opt/rh/gcc-toolset-13/root/usr/lib/gcc/architecture-linux-gnu/13/plugin

  2. Create the symbolic link: 

    # ln -s annobin.so gcc-annobin.so

Replace architecture with the architecture you use in your system:

  • aarch64
  • i686
  • ppc64le
  • s390x
  • x86_64

4.4. GCC Toolset 14
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Learn about information specific to the GCC Toolset version 14 and the tools contained in this version.

GCC Toolset 14 provides the following tools and versions.

Expand
Table 4.3. Tool versions in the GCC Toolset 14
NameVersionDescription

GCC

14.2.1

A portable compiler suite with support for C, C++, and Fortran.

binutils

2.41

A collection of binary tools and other utilities to inspect and manipulate object files and binaries.

dwz

0.14

A tool to optimize DWARF debugging information contained in ELF shared libraries and ELF executables for size.

annobin

12.70

A build security checking tool.

Note

In RHEL 9.5, the system GDB was rebased to version 14.2, and GDB is no longer included in the GCC Toolset.

4.4.2. C++ compatibility in the GCC Toolset 14
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The GNU Compiler Collection (GCC) in the GCC Toolset can use the following C++ standards:

Important

The compatibility information presented here apply only to the GCC from the GCC Toolset 14.

C++14

This language standard is available in the GCC Toolset 14.

Using the C++14 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 6 or later.

C++11

This language standard is available in the GCC Toolset 14.

Using the C++11 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 5 or later.

C++98
This language standard is available in the GCC Toolset 14. Binaries, shared libraries and objects built using this standard can be freely mixed regardless of being built with GCC from the GCC Toolset, Red Hat Developer Toolset, and RHEL 5, 6, 7 and 8.
C++17

This language standard is available in the GCC Toolset 14.

This is the default language standard setting for the GCC Toolset 14, with GNU extensions, equivalent to explicitly using option -std=gnu++17.

Using the C++17 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 10 or later.

C++20 and C++23

These language standards are available in the GCC Toolset 14 only as an experimental, unstable, and unsupported capability. Additionally, compatibility of objects, binary files, and libraries built using this standard cannot be guaranteed.

To enable the C++20 standard, add the command-line option -std=c++20 to your g++ command line.

To enable the C++23 standard, add the command-line option -std=c++23 to your g++ command line.

All of the language standards are available in both the standard compliant variant or with GNU extensions.

When mixing objects built by using the GCC Toolset with those built with the RHEL toolchain (particularly .o or .a files), the GCC Toolset toolchain should be used for any linkage. This ensures any newer library features provided only by the GCC Toolset are resolved at link time.

4.4.3. Specifics of GCC in the GCC Toolset 14
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Certain behaviors and requirements of the GCC Toolset 14 differ from the base Red Hat Enterprise Linux GNU Compiler Collection (GCC). These include automatic static linking of certain library features and the requirement to specify libraries after object files during linking.

Static linking of libraries

Certain more recent library features are statically linked into applications built with the GCC Toolset to support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a security erratum.

Important

Because of this additional security risk, developers are strongly advised not to statically link their entire application for the same reasons.

Specify libraries after object files when linking

In the GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux. However, the linker scripts use the names of the corresponding shared object files. As a consequence, the linker uses different symbol handling rules than expected, and does not recognize symbols required by object files when the option adding the library is specified before options specifying the object files: 

$ scl enable gcc-toolset-14 'gcc -lsomelib objfile.o'

Using a library from the GCC Toolset in this manner results in the linker error message undefined reference to symbol. To prevent this problem, follow the standard linking practice and specify the option adding the library after the options specifying the object files: 

$ scl enable gcc-toolset-14 'gcc objfile.o -lsomelib'

Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of GCC.

4.4.4. Specifics of binutils in the GCC Toolset 14
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Certain behaviors and requirements of binutils in the GCC Toolset 14 differ from the base Red Hat Enterprise Linux binutils. These include automatic static linking of certain library features and the requirement to specify libraries after object files during linking.

Static linking of libraries

Certain more recent library features are statically linked into applications built with the GCC Toolset to support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a security erratum.

Important

Because of this additional security risk, developers are strongly advised not to statically link their entire application for the same reasons.

Specify libraries after object files when linking

In the GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux. However, the linker scripts use the names of the corresponding shared object files. As a consequence, the linker uses different symbol handling rules than expected, and does not recognize symbols required by object files when the option adding the library is specified before options specifying the object files: 

$ scl enable gcc-toolset-14 'ld -lsomelib objfile.o'

Using a library from the GCC Toolset in this manner results in the linker error message undefined reference to symbol. To prevent this problem, follow the standard linking practice, and specify the option adding the library after the options specifying the object files: 

$ scl enable gcc-toolset-14 'ld objfile.o -lsomelib'

Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of binutils.

4.4.5. Specifics of annobin in the GCC Toolset 14
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Builds that use the GCC Toolset 14 and annobin can fail due to a synchronization issue between the annobin plugin and gcc. This causes the compiler to fail locating the gcc-annobin.so plugin file. 

cc1: fatal error: inaccessible plugin file
opt/rh/gcc-toolset-14/root/usr/lib/gcc/architecture-linux-gnu/14/plugin/gcc-annobin.so
expanded from short plugin name gcc-annobin: No such file or directory

To work around the problem, create a symbolic link in the plugin directory from the annobin.so file to the gcc-annobin.so file:

  1. Change to the plugin directory: 

    # cd /opt/rh/gcc-toolset-14/root/usr/lib/gcc/architecture-linux-gnu/14/plugin

  2. Create the symbolic link: 

    # ln -s annobin.so gcc-annobin.so

Replace architecture with the architecture you use in your system:

  • aarch64
  • i686
  • ppc64le
  • s390x
  • x86_64

4.5. GCC Toolset 15
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GCC Toolset 15 in Red Hat Enterprise Linux offers updated compilers and debuggers for C, C++, and Fortran. It enables building, testing, and optimizing applications with current features while maintaining system stability and support.

4.5.1. GCC Toolset 15 tools and versions
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The GCC Toolset 15 offers updated versions of development tools for building and debugging applications on Red Hat Enterprise Linux 8.

Expand
Table 4.4. Tool versions in the GCC Toolset 15

Name

Version

Description

GCC

15.1.1

A portable compiler suite with support for C, C++, and Fortran.

GDB

16.3

A command-line debugger for programs written in C, C++, and Fortran.

binutils

2.44

A collection of binary tools and other utilities to inspect and manipulate object files and binaries.

annobin

12.93

A build security checking tool.

dwz

0.16

A tool to optimize DWARF debugging information contained in ELF shared libraries and ELF executables for size.

4.5.2. C++ compatibility in the GCC Toolset 15
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The GNU Compiler Collection (GCC) Toolset 15 supports multiple C++ language standards. The default is C++17, with options for C++98, C++11, C++14, and experimental versions such as C++20, C++23, and C++26.

Important

This compatibility information applies only to GCC from the GCC Toolset 15.

The GCC compiler in the GCC Toolset 15 can use the following C++ standards:

C++98
This language standard is available in the GCC Toolset 15. Binaries, shared libraries, and objects built using this standard can be freely mixed regardless of being built with GCC from the GCC Toolset 15, Red Hat Developer Toolset, and RHEL 5, 6, 7, and 8.
C++11
This language standard is available in the GCC Toolset 15.
C++14
This language standard is available in the GCC Toolset 15.

Using the C++14 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 6 or later.

C++17
This language standard is available in the GCC Toolset 15.

This is the default language standard setting for the GCC Toolset 15, with GNU extensions, equivalent to explicitly using option -std=gnu++17.

Using the C++17 language version is supported when all C++ objects compiled with the appropriate flag have been built using GCC version 10 or later.

C++20 and C++23, and C++26
These language standards are available in the GCC Toolset 15 only as an experimental, unstable, and unsupported capabilities. Additionally, the compatibility of objects, binary files, and libraries built using these standards cannot be guaranteed.

To enable the C++20 standard, add the command-line option -std=c++20 to your g++ command line.

To enable the C++23 standard, add the command-line option -std=c++23 to your g++ command line.

To enable the C++26 standard, add the command-line option -std=c++26 to your g++ command line. All of the language standards are available in both the standard compliant variant or with GNU extensions.

Use the GCC Toolset 15 for linking when you combine objects built by using the GCC Toolset 15 with objects built by using the system toolchain, particularly .o or .a files. This ensures any newer library features provided only by the GCC Toolset 15 are resolved at link time.

4.5.3. Specifics of GCC in the GCC Toolset 15
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Certain behaviors and requirements of the GCC Toolset 15 differ from the base Red Hat Enterprise Linux GNU Compiler Collection (GCC). These include automatic static linking of certain library features and the requirement to specify libraries after object files during linking.

Static linking of libraries
Certain more recent library features are statically linked into applications built with the GCC Toolset 15 to support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a security erratum.
Important

Because of this additional security risk, developers are strongly advised not to statically link their entire application for the same reasons.

Specify libraries after object files when linking
In the GCC Toolset 15, libraries are linked using linker scripts, which might specify some symbols through static archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux. However, the linker scripts use the names of the corresponding shared object files. As a consequence, the linker uses different symbol handling rules than expected, and does not recognize symbols required by object files when the option adding the library is specified before options specifying the object files: 
$ scl enable gcc-toolset-15 'gcc -lsomelib objfile.o'

Using a library from the GCC Toolset 15 in this manner results in the linker error message undefined reference to symbol. To prevent this problem, follow the standard linking practice and specify the option by adding the library after the options specifying the object files:

+ 

$ scl enable gcc-toolset-15 'gcc objfile.o -lsomelib'

Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of GCC.

4.5.4. Specifics of binutils in the GCC Toolset 15
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Certain behaviors and requirements of binutils in the GCC Toolset 15 differ from the base Red Hat Enterprise Linux binutils. These include automatic static linking of certain library features and the requirement to specify libraries after object files during linking.

Static linking of libraries
GCC Toolset 15 statically links newer library features into applications to ensure compatibility across multiple Red Hat Enterprise Linux versions. Statically linked code can introduce minor security risks, because security updates require applications to be rebuilt. If a security vulnerability is discovered, Red Hat will notify developers to rebuild affected applications through a security advisory.
Important

Because of this additional security risk, developers are strongly advised not to statically link their entire application for the same reasons.

Specify libraries after object files when linking
In the GCC Toolset 15, libraries are linked using linker scripts which might specify some symbols through static archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux. However, the linker scripts use the names of the corresponding shared object files. As a consequence, the linker uses different symbol handling rules than expected, and does not recognize symbols required by object files when the option adding the library is specified before options specifying the object files: 
$ scl enable gcc-toolset-15 'ld -lsomelib objfile.o'

Using a library from the GCC Toolset 15 in this manner results in the linker error message undefined reference to symbol. To prevent this problem, follow the standard linking practice, and specify the option adding the library after the options specifying the object files:

+ 

$ scl enable gcc-toolset-15 'ld objfile.o -lsomelib'

Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of binutils.

4.6. Using the gcc-toolset container image
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Only the two latest GCC Toolset container images are supported. Container images of earlier GCC Toolset versions are unsupported.

The GCC Toolset 13 and the GCC Toolset 14 components are available in the GCC Toolset 13 Toolchain and GCC Toolset 14 Toolchain container images, respectively.

The GCC Toolset container image is based on the rhel9 base image and is available for all architectures supported by RHEL 9:

  • AMD and Intel 64-bit architectures
  • The 64-bit ARM architecture
  • IBM Power Systems, Little Endian
  • 64-bit IBM Z

4.6.1. GCC Toolset container image contents
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Tools versions provided in the GCC Toolset 14 container image match the GCC Toolset 14 components versions.

GCC Toolset 14 toolchain contents
The rhel9/gcc-toolset-14-toolchain container image consists of the following components:
Expand
ComponentPackage

gcc

gcc-toolset-14-gcc

g++

gcc-toolset-14-gcc-c++

gfortran

gcc-toolset-14-gcc-gfortran

To access and run the GCC Toolset container image, use a standard container engine like Podman. Authenticate with the registry, pull the image, and launch a container to access an isolated, pre-configured toolchain for development.

Prerequisites

  • Podman is installed.

Procedure

  1. Access the Red Hat Container Registry by using your Customer Portal credentials: 

    $ podman login registry.redhat.io
     
    Username: username
Password: **

  2. Pull the container image you require by running a relevant command as root: 

    # podman pull registry.redhat.io/rhel8/gcc-toolset-<toolset_version>-toolchain

    Replace toolset_version with the GCC Toolset version, for example 14.

    Note

    You can also set up your system to work with containers as a non-root user. For details, see Setting up rootless containers.

  3. Optional: Check that pulling was successful by running a command that lists all container images on your local system: 

    # podman images

  4. Run a container by launching a bash shell inside a container: 

    # podman run -it image_name /bin/bash

    The -i option creates an interactive session; without this option the shell opens and instantly exits.

    The -t option opens a terminal session; without this option you cannot type anything to the shell.

To pull and start using the GCC Toolset 14 Toolchain container image, access the registry, pull the image, and launch it.

Prerequisites

  • Podman is installed.

Procedure

  1. Access the Red Hat Container Registry by using your Customer Portal credentials: 

    $ podman login registry.redhat.io
     
    Username: username
Password: **

  2. Pull the container image as root: 

    # podman pull registry.redhat.io/rhel{ProductNumber}/gcc-toolset-14-toolchain

  3. Launch the container image with an interactive shell as root: 

    # podman run -it registry.redhat.io/rhel{ProductNumber}/gcc-toolset-14-toolchain /bin/bash

  4. Run the GCC Toolset tools as expected. For example, to verify the gcc compiler version, run: 

    bash-4.4$ gcc -v
     
    ...
gcc version 14.2.1 20240801 (Red Hat 14.2.1-1) (GCC)

  5. To list all packages provided in the container, run: 

    bash-4.4$ rpm -qa

4.7. Using the gcc-toolset-15 container image
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The gcc-toolset-15 container image provides a complete toolchain for building, testing, and troubleshooting C and C++ applications in a containerized environment.

The gcc-toolset-15 container image provides a GCC Toolset 15 toolchain for building, testing, and troubleshooting C and C++ applications on Red Hat Enterprise Linux (RHEL). By using this image, you can maintain a reproducible environment without installing packages directly on the host.

The image is part of the RHEL container collection. All included RPM packages originate from official RHEL repositories, ensuring the image follows standard RHEL lifecycle and support policies. This provides a portable, containerized alternative to traditional RPM-based delivery.

Deployment scenarios include:

  • Interactive development on a RHEL host by running an interactive container that mounts source code from the host.
  • Noninteractive builds in CI pipelines or scheduled jobs, with build scripts running inside the container and writing artifacts to host-mounted directories.
  • Evaluation and troubleshooting of GCC Toolset 15 behavior in an isolated environment without installing the toolchain on the host.

The gcc-toolset-15 image targets the same architectures provided by Red Hat Enterprise Linux (RHEL), including AMD64 and Intel 64 (x86_64), 64-bit ARM (aarch64), IBM Power, little endian (ppc64le), and 64-bit IBM Z (s390x).

For image-specific metadata, supported architectures, and tags, see the Red Hat container catalog entry for the gcc-toolset-15 container image.

If you plan to deploy the image across multiple architectures, ensure that you choose a tag that includes multi-architecture support or use architecture-specific tags according to your organization’s standards.

The gcc-toolset-15 image is available from Red Hat container registries. The exact path can differ depending on whether you use public registries, internal mirrors, or both. Placeholders for image locations are used below:

  • <REGISTRY> for the registry hostname.
  • <NAMESPACE> for the registry namespace that contains the gcc-toolset-15 image.
  • <TAG> for the image tag that corresponds to the GCC Toolset 15 level that you require.

Use your product documentation, internal image catalog, or registry UI to determine the correct values for <REGISTRY>, <NAMESPACE>, and <TAG>. Record these values for use in the procedures that follow.

To configure hosts to use the gcc-toolset-15 image, verify system requirements and install necessary container tools. For comprehensive guidelines, see Building, running, and managing containers.

Prerequisites

  • Administrator access to the RHEL host.
  • The host is registered and has access to required Red Hat Enterprise Linux repositories.
  • The host runs a supported Red Hat Enterprise Linux variant and architecture.
  • Ensure that the host has adequated resources for CPU, memory, and storage for build workloads.
  • The host has network access to the container registry or to an internal mirror.

Procedure

  1. Install the container management tools: 

    $ sudo dnf install -y container-tools

  2. Verify that podman is available: 

    $ podman --version

    If the command completes successfully, it prints the version. For example: 

    podman version 5.4.1

  3. Verify subscription and repository access: 

    $ sudo dnf repolist

    If required, configure subscription settings according to your environment so that the host can consume RHEL content and container registries.

4.7.4. Authenticating to the container registry
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To pull the gcc-toolset-15 image, you must log in to the container registry.

Prerequisites

  • container-tools are installed on the RHEL host.
  • You have the registry hostname and valid credentials.

Procedure

  1. Log in to the registry by using podman: 

    $ podman login <REGISTRY>

    Replace <REGISTRY> with your registry hostname.

  2. When prompted, enter your user name and password, or use the authentication mechanism that your organization provides.

Verification

  • Verify that the login and registry access were successful by searching for the gcc-toolset-15 image: 

    $ podman search <REGISTRY>/<NAMESPACE>/gcc-toolset-15**

4.7.5. Pulling the gcc-toolset-15 container image
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To use the gcc-toolset-15 image, pull it to your local system after authenticating to the registry.

Prerequisites

  • You have authenticated to the container registry.
  • You know the <REGISTRY>, <NAMESPACE>, and <TAG> values for the image. You can determine these details from the Red Hat Container Catalog or your internal image catalog.

Procedure

  1. Pull the image: 

    $ podman pull <REGISTRY>/<NAMESPACE>/gcc-toolset-15:<TAG>

    Replace <REGISTRY>, <NAMESPACE>, and <TAG> with the values you determined earlier.

Verification

  • Verify that the image is available locally: 

    $ podman images <REGISTRY>/<NAMESPACE>/gcc-toolset-15

    The output should display a table row containing the repository, tag, image ID, and size. For example: 

    REPOSITORY                            TAG     IMAGE ID      CREATED     SIZE
registry.redhat.io/.../gcc-toolset-15 latest  a1b2c3d4e5f6  2 days ago  540MB

To use the gcc-toolset-15 image for interactive development, run an interactive container that mounts source code from the host.

Prerequisites

  • The gcc-toolset-15 image is available locally.
  • You have a host directory containing the application source code, for example, /home/devuser/src.
  • You have read and write permissions for the host directory.

Procedure

  1. Start an interactive container that mounts the source directory and uses it as the working directory: 

    $ podman run --rm -it -v /home/devuser/src:/src -w /src <REGISTRY>/<NAMESPACE>/gcc-toolset-15:<TAG> /bin/bash

    Replace <REGISTRY>, <NAMESPACE>, and <TAG> with your specific values.

  2. Inside the container, verify that the source code is available: 

    # ls /src

  3. Build an application using GCC Toolset 15: 

    # gcc -o myapp main.c

    Build artifacts created in /src are stored on the host in /home/devuser/src.

  4. When the interactive session completes, exit the shell: 

    # exit

    Because the container was started with the --rm flag, it is removed automatically.

To perform noninteractive builds, run the gcc-toolset-15 image with a predefined build script that exits upon completion.

In CI systems, you can integrate this pattern by running podman run as part of a pipeline step. Use pipeline variables or configuration files to provide the values for <REGISTRY>, <NAMESPACE>, <TAG>, and host paths.

Ensure build scripts write logs and artifacts to host-mounted directories. This practice enables CI systems and administrators to inspect outputs after the container exits and to archive them as needed.

Prerequisites

  • The gcc-toolset-15 image is available locally.
  • A host directory for source and build scripts, for example, /srv/src.
  • A host directory for build output, for example, /srv/build-output.
  • A build script, for example, build.sh, that runs GCC Toolset 15 commands.

Procedure

  1. Prepare your build workflow. Ensure both the source and output directories on the host have appropriate permissions.

  2. Run the container in noninteractive mode: 

    $ podman run --rm -v /srv/src:/src -v /srv/build-output:/build-output -w /src <REGISTRY> / <NAMESPACE> /gcc-toolset-15: <TAG>  /src/build.sh

    In this example:

    • /src/build.sh is a script inside the container that performs the build.
    • Build artifacts and logs are written to /build-output, which maps to /srv/build-output on the host.

To maintain the gcc-toolset-15 image, monitor for updates including security fixes, bug fixes, and dependency changes. Track updates and errata by monitoring RHEL release notes, or internal advisories for new images that contain updated GCC Toolset 15 content.

Important
  • If you use an internal registry, mirror the updated image into the internal registry or rely on existing synchronization mechanisms.
  • Use internal paths for <REGISTRY> and <NAMESPACE> in all procedures.
  • Coordinate with the team that manages the internal registry to ensure that mirrors are updated inline with your rollout schedule.

Procedure

  1. Update to a new image tag: Consult the Red Hat Ecosystem Catalog or your internal registry to find the new image tag.

    1. Determine the <NEW_TAG> that corresponds to the updated gcc-toolset-15 image.

    2. Pull the new tag to your environment: 

      $ podman pull <REGISTRY>/<NAMESPACE>/gcc-toolset-15:<NEW_TAG>
    3. Update scripts, CI jobs, and documentation to reference <NEW_TAG> as appropriate.

  2. Remove outdated image tags after you complete validation and roll out the new tag, according to your retention policy: 

    $ podman rmi <REGISTRY>/<NAMESPACE>/gcc-toolset-15:<OLD_TAG>

Identify and resolve common issues when pulling or running the gcc-toolset-15 container image.

Common issues when pulling images

If podman pull fails:

  • Check registry login by running podman login <REGISTRY>.
  • Verify network connectivity to the registry.
  • Confirm that <REGISTRY>, <NAMESPACE>, and <TAG> values are correct.
  • If access is denied, verify that your subscription and registry permissions allow access to the gcc-toolset-15 image.
Common issues when running containers

If podman run fails:

  • Verify that the image is available locally by running podman images <REGISTRY>/<NAMESPACE>/gcc-toolset-15.

The output should display a table row containing the repository, tag, image ID, and size. For example: 

REPOSITORY                            TAG     IMAGE ID      CREATED     SIZE
registry.redhat.io/.../gcc-toolset-15 latest  a1b2c3d4e5f6  2 days ago  540MB
  • Check volume mount paths to ensure that host directories exist and that you have appropriate permissions.

  • Review container exit codes and logs to identify script or compiler errors.

    Collecting data for support
    When opening a support case, collect the following data:
  • The exact podman commands that you ran.
  • Full command output and error messages.
  • The values of <REGISTRY>, <NAMESPACE>, and <TAG> that you used.
  • Information about the host, including Red Hat Enterprise Linux version and architecture.

Review the following operational and security guidelines when using the gcc-toolset-15 container image in your environment.

Network and registry access control
Ensure that hosts can access the required registries or internal mirrors and that firewall settings allow necessary connections. Use internal registries where possible to centralize control of images. Consult your internal documentation for details on your organization’s registry layout and CI integration patterns.
Resource management for build workloads
Build containers can be resource-intensive. Use cgroup controls, systemd integration, or container runtime options to manage CPU, memory, and I/O usage on shared hosts.
Logging and auditing containerized builds
Configure build scripts to write logs to host-mounted directories. Integrate these logs with your logging and auditing infrastructure to track build activity and diagnose issues.
Security and compliance guidelines

Because the gcc-toolset-15 image is built from Red Hat Enterprise Linux (RHEL) repositories, it follows RHEL security practices. However, you should still follow these practicies:

  • Limit who can run containers on shared hosts.
  • Periodically review and update image tags to consume security fixes.
  • Use internal registries and scanning tools according to your organization’s policies.

4.8. Compiler toolsets
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RHEL 9 provides the following compiler toolsets as Application Streams. You can use these toolsets to build applications with different versions of languages and tools.

  • LLVM Toolset provides the LLVM compiler infrastructure framework, the Clang compiler for the C and C++ languages, the LLDB debugger, and related tools for code analysis.
  • Rust Toolset provides the Rust programming language compiler rustc, the cargo build tool and dependency manager, the cargo-vendor plugin, and required libraries.
  • Go Toolset provides the Go programming language tools and libraries. Go is alternatively known as golang.

For more details and information about usage, see the compiler toolsets user guides on the Red Hat Developer Tools page.

4.9. The Annobin project
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The Annobin project is an implementation of the Watermark specification project. Watermark specification project intends to add markers to Executable and Linkable Format (ELF) objects to determine their properties. The Annobin project consists of the annobin plugin and the annockeck program.

The annobin plugin scans the GNU Compiler Collection (GCC) command line, the compilation state. The compilation process, and generates the ELF notes. The ELF notes record how the binary was built and provide information for the annocheck program to perform security hardening checks.

The security hardening checker is part of the annocheck program and is enabled by default. It checks the binary files to determine whether the program was built with necessary security hardening options and compiled correctly. annocheck is able to recursively scan directories, archives, and RPM packages for ELF object files.

Note

The files must be in ELF format. annocheck does not handle any other binary file types.

The following section describes how to:

  • Use the annobin plugin
  • Use the annocheck program

4.9.1. Using the annobin plugin
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The following section describes how to:

  • Enable the annobin plugin
  • Pass options to the annobin plugin
4.9.1.1. Enabling the annobin plugin
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To add build security notes to binaries, enable the annobin plug-in by using command-line options with gcc or clang utilities.

Procedure

  • To enable the annobin plugin with gcc, use: 

    $ gcc -fplugin=annobin

    • If gcc does not find the annobin plugin, use: 

      $ gcc -iplugindir=/path/to/directory/containing/annobin/

      Replace /path/to/directory/containing/annobin/ with the absolute path to the directory that contains annobin.

    • To find the directory containing the annobin plugin, use: 

      $ gcc --print-file-name=plugin

  • To enable the annobin plugin with clang, use: 

    $ clang -fplugin=/path/to/directory/containing/annobin/

    Replace /path/to/directory/containing/annobin/ with the absolute path to the directory that contains annobin.

  • Optional: To remove the redundant annobin notes, use the objcopy utility: 

    $ objcopy --merge-notes file-name
4.9.1.2. Passing options to the annobin plugin
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To pass options to the annobin plugin, use the appropriate command-line arguments with gcc or clang.

Procedure

  • To pass options to the annobin plugin with gcc, use: 

    $ gcc -fplugin=annobin -fplugin-arg-annobin-option file-name

    Replace option with the annobin command line arguments and replace file-name with the name of the file.

    Example: verbose option with GCC

    • To display additional details about what annobin it is doing, use: 

      $ gcc -fplugin=annobin -fplugin-arg-annobin-verbose file-name

      Replace file-name with the name of the file.

  • To pass options to the annobin plugin with clang, use: 

    $ clang -fplugin=/path/to/directory/containing/annobin/ -Xclang -plugin-arg-annobin -Xclang option file-name

    Replace option with the annobin command line arguments and replace /path/to/directory/containing/annobin/ with the absolute path to the directory containing annobin.

    Example: verbose option with Clang

    • To display additional details about what annobin it is doing, use: 

      $ clang -fplugin=/usr/lib64/clang/10/lib/annobin.so -Xclang -plugin-arg-annobin -Xclang verbose file-name

      Replace file-name with the name of the file.

4.9.2. Using the annocheck program
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The following section describes how to use annocheck to examine:

  • Files
  • Directories
  • RPM packages
  • annocheck extra tools
Note

annocheck recursively scans directories, archives, and RPM packages for ELF object files. The files have to be in the ELF format. annocheck does not handle any other binary file types.

4.9.2.1. Using annocheck to examine files
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To verify hardening options and build security notes of ELF files, examine the files by using the annocheck tool.

Procedure

  • To examine a file, use: 

    $ annocheck file-name

    Replace file-name with the name of a file.

Note

The files must be in ELF format. annocheck does not handle any other binary file types. annocheck processes static libraries that contain ELF object files.

Additional resources

  • For more information about annocheck and possible command line options, see the annocheck man page on your system.
4.9.2.2. Using annocheck to examine directories
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To examine ELF files in a directory, use the annocheck tool, which recursively scans directories, subdirectories, and archives.

Procedure

  • To scan a directory, use: 

    $ annocheck directory-name

    Replace directory-name with the name of a directory. annocheck automatically examines the contents of the directory, its sub-directories, and any archives and RPM packages within the directory.

Note

annocheck only looks for ELF files. Other file types are ignored.

Additional resources

  • For more information about annocheck and possible command line options, see the annocheck man page on your system.
4.9.2.3. Using annocheck to examine RPM packages
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To examine ELF files in an RPM package, use the annocheck tool, which recursively scans all ELF files inside the package.

Procedure

  • To scan an RPM package, use: 

    $ annocheck rpm-package-name

    Replace rpm-package-name with the name of an RPM package. annocheck recursively scans all the ELF files inside the RPM package.

Note

annocheck only looks for ELF files. Other file types are ignored.

  • To scan an RPM package with provided debug info RPM, use: 

    $ annocheck rpm-package-name --debug-rpm debuginfo-rpm

    Replace rpm-package-name with the name of an RPM package, and debuginfo-rpm with the name of a debug info RPM associated with the binary RPM.

Additional resources

  • For more information about annocheck and possible command line options, see the annocheck man page on your system.
4.9.2.4. Using annocheck extra tools
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annocheck includes multiple tools for examining binary files. You can enable these tools with the command-line options.

The following section describes how to enable the:

  • built-by tool
  • notes tool
  • section-size tool

You can enable multiple tools at the same time.

Note

The hardening checker is enabled by default.

4.9.2.4.1. Enabling the built-by tool
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To find the name of the compiler that built a specific binary file, you can use the annocheck built-by tool.

Procedure

  • To enable the built-by tool, use: 

    $ annocheck --enable-built-by

Additional resources

  • For more information about the built-by tool, see the --help command-line option.
4.9.2.4.2. Enabling the notes tool
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To display the notes stored inside a binary file created by the annobin plug-in, you can use the annocheck notes tool.

Procedure

  • To enable the notes tool, use: 

    $ annocheck --enable-notes

    The notes are displayed in a sequence sorted by the address range.

Additional resources

  • For more information about the notes tool, see the --help command-line option.
4.9.2.4.3. Enabling the section-size tool
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To display the size of named sections, you can use the annocheck section-size tool.

Procedure

  • To enable the section-size tool, use: 

    $ annocheck --section-size=name

    Replace name with the name of the named section. The output is restricted to specific sections. A cumulative result is produced at the end.

Additional resources

  • For more information about the section-size tool, see the --help command-line option.
4.9.2.4.4. Hardening checker basics
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The hardening checker is enabled by default. You can disable the hardening checker with the --disable-hardened command-line option.

4.9.2.4.4.1. Hardening checker options
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The annocheck tool verifies binaries for various hardening options, such as stack protection, PIC/PIE usage, and secure linker settings. The following options are checked:

  • Lazy binding is disabled using the -z now linker option.
  • The program does not have a stack in an executable region of memory.
  • The relocations for the GOT table are set to read only.
  • No program segment has all three of the read, write and execute permission bits set.
  • There are no relocations against executable code.
  • The runpath information for locating shared libraries at runtime includes only directories rooted at /usr.
  • The program was compiled with annobin notes enabled.
  • The program was compiled with the -fstack-protector-strong option enabled.
  • The program was compiled with -D_FORTIFY_SOURCE=2.
  • The program was compiled with -D_GLIBCXX_ASSERTIONS.
  • The program was compiled with -fexceptions enabled.
  • The program was compiled with -fstack-clash-protection enabled.
  • The program was compiled at -O2 or higher.
  • The program does not have any relocations held in a writeable.
  • Dynamic executables have a dynamic segment.
  • Shared libraries were compiled with -fPIC or -fPIE.
  • Dynamic executables were compiled with -fPIE and linked with -pie.
  • If available, the -fcf-protection=full option was used.
  • If available, the -mbranch-protection option was used.
  • If available, the -mstackrealign option was used.
4.9.2.4.4.2. Disabling the hardening checker
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To skip security checks during binary analysis, disable the hardening checker by using the annocheck utility.

Procedure

  • To scan the notes in a file without the hardening checker, use: 

    $ annocheck --enable-notes --disable-hardened file-name

    Replace file-name with the name of a file.

4.9.3. Specifics of annobin in the GCC Toolset 12
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Under some circumstances, due to a synchronization issue between annobin and gcc in the GCC Toolset 12, your compilation can fail with an error message that looks similar to the following: 

cc1: fatal error: inaccessible plugin file
opt/rh/gcc-toolset-12/root/usr/lib/gcc/architecture-linux-gnu/12/plugin/gcc-annobin.so
expanded from short plugin name gcc-annobin: No such file or directory

To work around the problem, create a symbolic link in the plugin directory from the annobin.so file to the gcc-annobin.so file:

  1. Change to the plugin directory: 

    # cd /opt/rh/gcc-toolset-12/root/usr/lib/gcc/architecture-linux-gnu/12/plugin

  2. Create the symbolic link: 

    # ln -s annobin.so gcc-annobin.so

Replace architecture with the architecture you use in your system:

  • aarch64
  • i686
  • ppc64le
  • s390x
  • x86_64

Legal Notice
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Except as otherwise noted below, the text of and illustrations in this documentation are licensed by Red Hat under the Creative Commons Attribution–Share Alike 3.0 Unported license . If you distribute this document or an adaptation of it, you must provide the URL for the original version.
Red Hat, as the licensor of this document, waives the right to enforce, and agrees not to assert, Section 4d of CC-BY-SA to the fullest extent permitted by applicable law.
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