Chapter 9. Compiler and Tools

GNU Compiler Collection (GCC) implements support for on-line patching of multi-threaded code for Linux on System z binaries. Selecting specific functions for hot-patching is enabled by using a "function attribute" and hot-patching for all functions can be enabled using the -mhotpatch command-line option.

Enabling hot-patching has a negative impact on software size and performance. It is therefore recommended to use hot-patching for specific functions instead of enabling hot patch support for all functions.

Hot-patching support for Linux on System z binaries was a Technology Preview for Red Hat Enterprise Linux 7.0. With the release of Red Hat Enterprise Linux 7.1, it is now fully supported.

Red Hat Enterprise Linux 7 includes the Performance Application Programming Interface (PAPI). PAPI is a specification for cross-platform interfaces to hardware performance counters on modern microprocessors. These counters exist as a small set of registers that count events, which are occurrences of specific signals related to a processor's function. Monitoring these events has a variety of uses in application performance analysis and tuning.

In Red Hat Enterprise Linux 7.1, PAPI and the related libpfm libraries have been enhanced to provide support for IBM POWER8, Applied Micro X-Gene, ARM Cortex A57, and ARM Cortex A53 processors. In addition, the events sets have been updated for Intel Xeon, Intel Xeon v2, and Intel Xeon v3 procesors.

OProfile is a system-wide profiler for Linux systems. The profiling runs transparently in the background and profile data can be collected at any time. In Red Hat Enterprise Linux 7.1, OProfile has been enhanced to provide support for the following processor families: Intel Atom Processor C2XXX, 5th Generation Intel Core Processors, IBM POWER8, AppliedMicro X-Gene, and ARM Cortex A57.

Red Hat Enterprise Linux 7.1 features the java-1.8.0-openjdk packages, which contain the latest version of the Open Java Development Kit, OpenJDK8, that is now fully supported. These packages provide a fully compliant implementation of Java SE 8 and may be used in parallel with the existing java-1.7.0-openjdk packages, which remain available in Red Hat Enterprise Linux 7.1.

Java 8 brings numerous new improvements, such as Lambda expressions, default methods, a new Stream API for collections, JDBC 4.2, hardware AES support, and much more. In addition to these, OpenJDK8 contains numerous other performance updates and bug fixes.

The deprecated snap tool has been removed from the powerpc-utils package. Its functionality has been integrated into the sosreport tool.

Red Hat Enterprise Linux 7.1 implements support for the 64-bit PowerPC little-endian architecture in the GNU Debugger (GDB).

Tuna is a tool that can be used to adjust scheduler tunables, such as scheduler policy, RT priority, and CPU affinity. In Red Hat Enterprise Linux 7.1, the Tuna GUI has been enhanced to request root authorization when launched, so that the user does not have to run the desktop as root to invoke the Tuna GUI. For further information on Tuna, see the Tuna User Guide.

With Red Hat Enterprise Linux 7.1, the crash packages are no longer a dependency of the abrt packages. Therefore, crash has been removed from the default installation of Red Hat Enterprise Linux  7 in order to keep the installation minimal. Now, users have to select the Debugging Tools option in the Anaconda installer GUI for the crash packages to be installed.

As a Technology Preview, the network-querying capabilities of the ethtool utility have been enhanced for Red Hat Enterprise Linux 7.1 on IBM System z. As a result, when using hardware compatible with the improved querying, ethtool now provides improved monitoring options, and displays network card settings and values more accurately.

Intel has issued erratum HSW136 concerning Transactional Synchronization Extensions (TSX) instructions. Under certain circumstances, software using the Intel TSX instructions may result in unpredictable behavior. TSX instructions may be executed by applications built with the Red Hat Enterprise Linux 7.1 GCC under certain conditions. These include the use of GCC's experimental Transactional Memory support (-fgnu-tm) when executed on hardware with TSX instructions enabled. Users of Red Hat Enterprise Linux 7.1 are advised to exercise further caution when experimenting with Transaction Memory at this time, or to disable TSX instructions by applying an appropriate hardware or firmware update.