Chapter 2. Red Hat Developer Toolset 7.1 Release
2.1. Changes in Red Hat Developer Toolset 7.1
2.1.1. Upgraded Components
- GCC to version 7.3.1
2.1.2. Compiler Toolsets in Red Hat Developer Tools
2.1.3. Container Images
- The updated
rhscl/devtoolset-7-toolchain-rhel7image, which contains the following Red Hat Developer Toolset components:
devtoolset-7-binutilscomponent is pulled by
rhscl/devtoolset-7-perftools-rhel7image, which contains the following components:
2.2.1. List of Components
- GNU Compiler Collection (GCC)
- GNU Debugger (GDB)
Performance Monitoring Tools
2.2.2. Main Features
- The Red Hat Developer Toolset version of the GNU Compiler Collection (GCC) has been upgraded to version 7.3.1 with numerous new features and bug fixes.
2.3. Known Issues
- In Red Hat Developer Toolset, libraries are linked via 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 names of the respective 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, such as:
gcc -lsomelib objfile.oSuch use of a library from Red Hat Developer Toolset results in linker error messages
undefined reference to symbol. To enable successful symbol resolution and linking, follow the standard linking practice and specify the option adding the library after the options specifying the object files:
gcc objfile.o -lsomelibNote that this recommendation applies when using the version of GCC available as a part of Red Hat Enterprise Linux, too.
- On the 64-bit ARM architecture, the GDB debugger provides only limited support for unaligned hardware watchpoints used by the
awatchGDB commands. As a consequence, GDB running on such systems fails to register some watchpoint hits and subsequently does not stop the debugged program.To work around this problem, set the watchpoint start address to a manually corrected memory address aligned down to a multiple of 8 bytes. An unaligned ending address does not have this negative effect. Note that with this workaround, GDB registers further hits for the watchpoint in the additional part of memory, which is not interesting for the user.
- When the user installs only the devtoolset-7-dyninst or devtoolset-7-systemtap packages, the devtoolset-7-dyninst-devel package is not pulled. As a consequence, Dyninst fails to work correctly. The same problem applies also to SystemTap with the Dyninst back end when the
stap --dyninstcommand is used. To work around this problem, manually install the devtoolset-7-dyninst-devel package, enable the devtoolset-7 Software Collection, and then run the
- GCC in Red Hat Developer Toolset 3.x contained the libasan package, which might have conflicted with the system version of libasan. As a consequence, depending on which libasan was present in the system, the
-fsanitize=addresstool worked only either with the system GCC or with the Red Hat Developer Toolset version of GCC, but not with both at the same time. To prevent the described conflict, in Red Hat Developer Toolset 4.x and later versions, the package was renamed to libasanN, where N is a number. However, if the Red Hat Software Collections repository is enabled, the problem can occur after the system update because the system version of libasan is available in an earlier version than the Red Hat Developer Toolset 3.x version, which is still available in the repository. To work around this problem, exclude this package while updating:
~]$ yum update --exclude=libasan
- OProfile 1.2.0 shipped in Red Hat Developer Toolset 7.1 works on all supported architectures, with the exception of IBM z Systems, where only the ocount tool works on the following models: z196, zEC12, and z13. operf and the other tools, such as oparchive or opannotate, do not work on IBM z Systems. For profiling purposes, users are recommended to use the Red Hat Enterprise Linux 7 system OProfile 0.9.9 version, which supports opcontrol with
TIMERsoftware interrupts.Note that for correct reporting of data collected by OProfile 0.9.9, the corresponding opreport utility is necessary. Thus opcontrol-based profiling should be performed with Red Hat Developer Toolset disabled because the reporting tools from Red Hat Developer Toolset cannot process data collected within opcontrol legacy mode correctly.
- The default Valgrind gdbserver support (
--vgdb=yes) can cause certain register and flags values to be not always up-to-date due to optimizations done by the Valgrind core. The GDB utility is therefore unable to show certain parameters or variables of programs running under Valgrind. To work around this problem, use the
--vgdb=fullparameter. Note that programs might run slower under Valgrind when this parameter is used.
- multiple components
- The devtoolset-7-package_name-debuginfo packages can conflict with the corresponding packages from the base Red Hat Enterprise Linux system or from other versions of Red Hat Developer Toolset. This namely applies to devtoolset-7-gcc-debuginfo, devtoolset-7-ltrace-debuginfo, devtoolset-7-valgrind-debuginfo, and might apply to other debuginfo packages, too. A similar conflict can also occur in a multilib environment, where 64-bit debuginfo packages conflict with 32-bit debuginfo packages.For example, on Red Hat Enterprise Linux 7, devtoolset-7-gcc-debuginfo conflicts with three packages: gcc-base-debuginfo, gcc-debuginfo, and gcc-libraries-debuginfo. On Red Hat Enterprise Linux 6, devtoolset-7-gcc-debuginfo conflicts with one package: gcc-libraries-debuginfo. As a consequence, if conflicting debuginfo packages are installed, attempts to install Red Hat Developer Toolset 7.1 can fail with a transaction check error message similar to the following examples:
file /usr/lib/debug/usr/lib64/libitm.so.1.0.0.debug from install of gcc-base-debuginfo-4.8.5-16.el7.x86_64 conflicts with file from package devtoolset-7-gcc-debuginfo-7.2.1-1.el7.x86_64
file /usr/lib/debug/usr/lib64/libtsan.so.0.0.0.debug from install of gcc-debuginfo-4.8.5-16.el7.x86_64 conflicts with file from package devtoolset-7-gcc-debuginfo-7.2.1-1.el7.x86_64
file /usr/lib/debug/usr/lib64/libitm.so.1.0.0.debug from install of devtoolset-7-gcc-debuginfo-7.2.1-1.el6.x86_64 conflicts with file from package gcc-libraries-debuginfo-7.1.1-2.3.1.el6_9.x86_64To work around the problem, manually uninstall the conflicting debuginfo packages prior to installing Red Hat Developer Toolset 7.1. It is advisable to install only the relevant debuginfo packages when necessary and expect such problems to happen.
- Red Hat Developer Toolset primarily aims to provide a compiler for development of user applications for deployment on multiple versions of Red Hat Enterprise Linux. Operating system components, kernel modules and device drivers generally correspond to a specific version of Red Hat Enterprise Linux, for which the supplied base OS compiler is recommended.
- Red Hat Developer Toolset 7.1 supports only C, C++ and Fortran development. For other languages, invoke the system version of GCC available on Red Hat Enterprise Linux.
- Building an application with Red Hat Developer Toolset 7.1 on Red Hat Enterprise Linux (for example, Red Hat Enterprise Linux 7) and then executing that application on an earlier minor version (such as Red Hat Enterprise Linux 6.7.z) may result in runtime errors due to differences in non-toolchain components between Red Hat Enterprise Linux releases. Users are advised to check compatibility carefully. Red Hat supports only execution of an application built with Red Hat Developer Toolset on the same, or a later, supported release of Red Hat Enterprise Linux than the version used to build that application.
- Valgrind must be rebuilt without Red Hat Developer Toolset's GCC installed, or it will be used in preference to Red Hat Enterprise Linux system GCC. The binary files shipped by Red Hat are build using the system GCC. For any testing, Red Hat Developer Toolset's GDB should be used.
- All code in the non-shared library
libstdc++_nonshared.ain Red Hat Developer Toolset 7.1 is licensed under the GNU General Public License v3 with additional permissions granted under Section 7, described in the GCC Runtime Library Exception version 3.1, as published by the Free Software Foundation.
- The compiler included in Red Hat Developer Toolset emits newer DWARF debugging records than previous compilers available on Red Hat Enterprise Linux. These new debugging records improve the debugging experience in a variety of ways, particularly for C++ and optimized code. However, certain tools are not yet capable of handling the newer DWARF debug records. To generate the older style debugging records, use the options
- Some newer library features are statically linked into applications built with Red Hat Developer Toolset to support execution on multiple versions of Red Hat Enterprise Linux. This adds a small additional security risk because regular Red Hat Enterprise Linux errata would not change this code. If the need for developers to rebuild their applications due to such an issue arises, Red Hat will signal this in a security erratum. Developers are strongly advised not to statically link their entire application for the same reasons.
- Note that error messages related to a missing libitm library when using the
-fgnu-tmoption require the libitm package to be installed. You can install the package with the following command:
yum install libitm
- To use the ccache utility with GCC included in Red Hat Developer Toolset, set your environment correctly. For example:
scl enable devtoolset-7 '/usr/lib64/ccache/gcc -c foo.c'Alternatively, you can create a shell with the Red Hat Developer Toolset version of GCC as the default compiler:
scl enable devtoolset-7 'bash'After you have created the shell, run the following two commands:
gcc -c foo.c
- Because the elfutils libraries contained in Red Hat Developer Toolset 7.1 are linked to a client application statically, caution is advised when passing handles to
libasmdata structures to external code and when passing handles received from external code to
libasm.Be especially careful when an external library, which is linked dynamically against the system version of elfutils, is passed a pointer to a structure that comes from the Red Hat Developer Toolset 7.1 version of elfutils (or vice versa).Generally, data structures used in the Red Hat Developer Toolset 7.1 version of elfutils are not compatible with the Red Hat Enterprise Linux system versions, and structures coming from one should never be touched by the other.In applications that use the Red Hat Developer Toolset 7.1 libraries, all code that was linked against the system version of the libraries should be recompiled against the libraries included in Red Hat Developer Toolset 7.1.
- The elfutils
EBLlibrary, which is used internally by
libdw, was amended not to open back ends dynamically. Instead, a selection of back ends is compiled in the library itself: the 32-bit AMD and Intel architecture, AMD64 and Intel 64 systems, Intel Itanium, IBM z Systems, 32-bit IBM Power Systems, 64-bit IBM Power Systems, IBM POWER, big endian, and the 64-bit ARM architecture. Some functionality may not be available if the client wishes to work with ELF files from architectures other than those mentioned above.
- Some packages managed by the scl utility include privileged services that require sudo. The system sudo clears environment variables and so Red Hat Developer Toolset includes its own sudo shell script, wrapping
scl enable. This script does not currently parse or pass normal sudo options, only
sudo COMMAND ARGS .... In order to use the system version of sudo from within a Red Hat Developer Toolset-enabled shell, use the
- Intel have issued erratum HSW136 concerning TSX (Transactional Synchronization Extensions) instructions. Under certain circumstances, software using the Intel TSX instructions may result in unpredictable behavior. TSX instructions may be executed by applications built with Red Hat Developer Toolset GCC under certain conditions. These include use of GCC's experimental Transactional Memory support (using the
-fgnu-tmoption) when executed on hardware with TSX instructions enabled. The users of Red Hat Developer Toolset 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.
- To use the Memory Protection Extensions (MPX) feature in GCC, the Red Hat Developer Toolset version of the
libmpxlibrary is required, otherwise the application might not link properly.
- The two binutils linkers,
ld, have different ways of handling hidden symbols, which leads to incompatibilities in their behavior. Previously, the
ldlinkers had inconsistent and incorrect behavior with regard to shared libraries and hidden symbols. There were two scenarios:
- If a shared library referenced a symbol that existed elsewhere in both hidden and non-hidden versions, the
goldlinker produced a bogus warning message about the hidden version.
- If a shared library referenced a symbol that existed elsewhere only as a hidden symbol, the
goldlinker created an executable, even though it could not work.
goldlinker has been updated so that it no longer issues bogus warning messages about hidden symbols that also exist in a non-hidden version. The second scenario cannot be solved in the linker. It is up to the programmer to ensure that a non-hidden version of the symbol is available when the application is run.As a result, the two linkers' behavior is closer, but they still differ in case of a reference to a hidden symbol that cannot be found elsewhere in a non-hidden version. Unfortunately, there is not a single correct behavior for this situation, so the linkers are allowed to differ.
- The valgrind-openmpi subpackage is no longer provided with Valgrind in Red Hat Developer Toolset. The devtoolset-<version>-valgrind-openmpi subpackages previously caused incompatibility issues with various Red Hat Enterprise Linux minor releases and problems with rebuilding. Users are recommended to use the latest Red Hat Enterprise Linux system version of the valgrind and valgrind-openmpi packages if they need to run Valgrind against their programs that are built against the openmpi-devel libraries.