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Revision as of 17:27, 28 December 2023 by Codonell (talk | contribs) (Update gdb to 14.1 as the gdb team has rolled out the update already.)


GNU Toolchain Update (gcc 14.0, binutils 2.41, glibc 2.39, gdb 14.1)

This is a proposed Change for Fedora Linux.
This document represents a proposed Change. As part of the Changes process, proposals are publicly announced in order to receive community feedback. This proposal will only be implemented if approved by the Fedora Engineering Steering Committee.


Summary

Update the Fedora 40 GNU Toolchain to gcc 14.0, binutils 2.41, glibc 2.39 and gdb 14.1.

The set of core GNU Toolchain packages for Fedora 40 are as follows:

  • GNU C Compiler 14.0
    • Associated runtimes for C++ (libstdc++), Go (gccgo), OpenMP (gomp), Fortran (gfortran), D (phobos), Objective C/C++.
  • GNU Binary Utilities 2.41
  • GNU C Library 2.39
  • GNU Debugger 14.1 (immediately available in Fedora 39)

The gcc 14.0 change will be tracked in this top-level GNU Toolchain system-wide update.

The "Porting to Modern C" system-wide change requested is tracked here: https://fedoraproject.org/wiki/Changes/PortingToModernC

The binutils 2.41 change will be tracked in this top-level GNU Toolchain system-wide update.

The glibc 2.39 change will be tracked in this top-level GNU Toolchain system-wide update.

The gdb 14.1 update was rolled out across all Fedora releases and the move to 14+ will be handled in the same fashion. The debugger is capable of debugging the binary artifacts produced by the rest of the system toolchain.

Owner

Current status

  • Targeted release: Fedora Linux 40
  • Last updated: 2023-12-28
  • Announced
  • Discussion thread
  • FESCo issue: <will be assigned by the Wrangler>
  • Tracker bug: <will be assigned by the Wrangler>
  • Release notes tracker: <will be assigned by the Wrangler>
  • Updated redhat-rpm-config: [X] (TODO: Check if redhat-rpm-config needs updating for the new toolchain)
  • Are config.guess and config.sub up to date from upstream? No. Update required.
  • GCC Ada SONAME bump: [X] (TODO: Check if Ada bumped the SONAME)
    • Yes, the Ada SONAME has changed to libgnat-14.so from libgnat-13.so.
  • Did we rebuild the packages in the side-tag before merging? This will be coordinated with the Ada developers.

Detailed Description

The GNU Compiler Collection, GNU Binary Utilities, GNU C Library, and the GNU Debugger make up the core part of the GNU Toolchain and it is useful for our users to transition these components as a complete implementation when making a new release of Fedora.

The GNU Compiler Collection is expected to release version 14.0, before the Fedora 40 release. It will contain many new features, documented here: https://gcc.gnu.org/gcc-14/changes.html. The latest point release for gcc 14 will be included in Fedora 40, this will most probably be 14.0. Enabling warnings and other features related to porting to modern C will be tracked as part of the Port to Modern C system-wide change request.

The GNU Binutils version 2.41 was released before Fedora 40; and we have already been using this version of binutils in Fedora Rawhide successfully to build the distribution. Given the present schedule for Fedora 40 we will continue to use Binutils 2.41.

The GNU C Library version 2.39 is expected to be release before Fedora 40; we have started closely tracking the glibc 2.39 development code in Fedora Rawhide and are addressing any issues as they arise. Given the present schedule Fedora 40 will branch after the release of glibc 2.39. However, the mass rebuild schedule means Fedora 40 will mass rebuild (if required) before the final release of glibc 2.39, but after the ABI is frozen.

The GNU Debugger version 14.1 has already been rolled out to Fedora 39 and will continue to roll out to other non-EOL releases.

Enable GNU TLS Descriptors

This update will enable the use of GNU TLS Descriptors for x86_64 to match what has already been in place in AArch64. This allows x86_64 to use faster static TLS access modes if static TLS space remains available. This is an internal implementation detail of the way in which thread local storage is implemented. Recent advances in the toolchain allow this to be used along with a limited set of libraries that use static TLS access modes and are loaded dynamically. The dynamic loader has additional tunables to start applications with more reserved static TLS space if required for better performance or for dynamically loaded libraries.

Benefit to Fedora

Stays up to date with latest features, improvements, security and bug fixes from gcc, glibc, binutils, and gdb upstream.

The goal is to track and transition to the latest components of the GNU Toolchain.

Scope

  • Proposal owners: Fedora Toolchain Team (gcc, glibc, binutils, gdb, ...) developers need to ensure that gcc, glibc, binutils, and gdb in rawhide are stable and ready for the Fedora 40 branch.
  • Other developers: Given that glibc is backwards compatible and we have been testing the new glibc in rawhide it should make very little impact when updated, except for the occasional deprecation warnings and removal of legacy interfaces from public header files.
  • Release engineering: A mass rebuild is strongly encouraged; #11865
  • Policies and guidelines: N/A (not needed for this Change)
  • Trademark approval: N/A (not needed for this Change)
  • Alignment with Objectives: N/A


Upgrade/compatibility impact

The compiler, the static linker and the the library are backwards compatible with the previous version of Fedora.

Some source changes may be required for gcc 14 rebase: https://gcc.gnu.org/gcc-14/changes.html

Any source level changes required for glibc 2.39 will be noted here: https://sourceware.org/glibc/wiki/Release/2.39#Packaging_Changes

How To Test

The GNU Compiler Collection has its own test suite which is run during the package build and examined by the gcc developers before being uploaded.

The GNU C Library has its own test suite which is run during the package build and examined by the glibc developers before being uploaded. This test suite has over 6200 tests that run to verify the correct operation of the library. In the future we may also run the microbenchmark to look for performance regressions.

The GNU Binutils has its own test suite which is run during the package build and examined by binutils developers before being uploaded. The regression test suite is run to verify the correct operation of the static linker and attendant utilities.

The GNU Debugger has its own test suite which is run during the package build and examined by gdb developers before being uploaded. The regression test suite is run to verify the correct operation of the debugger.

User Experience

Upgrading the 4 main GNU Toolchain components (gcc, binutils, glibc, and gdb) ensures that users have an up to date working system compiler, assembler, static linker, core language runtimes (C, C++, etc), dyanmic linker, and debugger. All of these components are being updated to provide support for newer language features, and hardware features; enabling users to make use of these features for their applications. In some cases the components are updated in a synchronized fashion if a feature requires support across the components that constitute the implementation e.g. compiler feature that requires language library support.

Dependencies

All packages do not need to be rebuilt due to backwards compatibility. However, it is advantageous if a mass rebuild is performed during the Fedora 40 cycle. The mass rebuild would ensure all packages can be built with the newer compiler and core runtime.

Contingency Plan

  • Contingency mechanism glibc: If glibc 2.39 proves too disruptive to compiling the distribution we could revert to 2.38, but given that Rawhide has started tracking glibc 2.39, no show-stopper problems are expected. At this point we can still revert to upstream version 2.38 if insurmountable problems appear, but to do so may require a mass rebuild to remove new symbols from the ABI/API.
  • Contingency mechanism binutils: If binutils 2.41 proves too distruptive to assembling and linking the distribution we could revert to 2.40, but given that Rawhide is using 2.41, no show-stopper problems are expected. At this point we can still revert if insurmountable problems appear, but to do so may require a mass rebuild if the defects involve generated binaries.
  • Contingency mechanism for gcc: If gcc 14 proves too disruptive to compiling the distribution we could revert to gcc 13.2.


  • Contingency deadline: Fedora mass rebuild on 2024-01-17.
  • Blocks release?
    • Yes, upgrading to gcc 14.0 does block the release.
    • Yes, upgrading to binutils 2.41 does block the release.
    • Yes, upgrading to glibc 2.39 does block the release.
    • No, upgrading to gdb 14+ does not block the release.


Documentation

The gcc manual contains the documentation for the release and doesn't need any more additional work.

The binutils manual contains the documentation for the release and doesn't need any more additional work.

The glibc manual contains the documentation for the release and doesn't need any more additional work.

The gdb manual contains the documentation for the release and doesn't need any more additional work.

Release Notes

See https://gcc.gnu.org/gcc-14/changes.html for the GNU Compiler Collection version 14 release notes.

The GNU C Library version 2.39 will be released at the beginning of February 2024. The current NEWS notes can be seen here as they are added: https://sourceware.org/git/?p=glibc.git;a=blob;f=NEWS;hb=HEAD

The GNU Binary Utilities version 2.41 was released August 2023. The current release notes: https://sourceware.org/pipermail/binutils/2023-July/128719.html

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