Changes/GNUToolchainF35

GNU Toolchain update (gcc 11, glibc 2.34, binutils 2.37)

Summary

Switch the Fedora 35 GNU Toolchain to gcc 11 (lastest point release), binutils 2.37, and glibc 2.34.

The gcc 11 is already included in Fedora 34, but the release will be updated to the latest point release. The glibc 2.34 change will be tracked in this top-level GNU Toolchain system-wide update. Likewise the binutils 2.37 release will be tracked in this top-level GNU Toolchain system-wide update.

Owner

• Name: Carlos O'Donell
• Email: carlos@redhat.com

Current status

• Targeted release: Fedora 35
• Last updated: 2021-06-22
• 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>

Detailed Description

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

The GNU Compiler Collection has already released version 11 containing many new features documented here: https://gcc.gnu.org/gcc-11/changes.html. The latest point release for gcc 11 will be included in Fedora 35, this will be either 11.1 (already released in April) or 11.2 (released later).

The GNU C Library version 2.34 will be released at the beginning of August 2021; we have started closely tracking the glibc 2.34 development code in Fedora Rawhide and are addressing any issues as they arise. Given the present schedule Fedora 35 will branch after the glibc 2.34 upstream release. However, the mass rebuild schedule means Fedora 35 will mass rebuild (if required) after glibc 2.34 upstream freezes ABI for release, but before the actual release, so careful attention must be paid to any last minute ABI changes.

The GNU Binutils version 2.37 will be released near the end of July 2021;

Benefit to Fedora

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

The gcc and glibc teams will need to move their respective upstream projects to a releasable state. For GCC this includes correctly building Fedora rawhide.

• Other developers: Developers need to ensure that gcc, binutils, and glibc in rawhide are stable and ready for the Fedora 35 branch. 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. An update to GCC 11.2 would be a minimal change with bug fixes. The binutils 2.37 update has the broadest scope for change and generated object files should be reviewed and failures to build analyzed.

• Release engineering: #Releng issue number

A mass rebuild is strongly encouraged. The glibc 2.34 release merges libpthread.so into libc.so and it would be important to remove DT_NEEDED on libpthread.so from all distribution binaries.

• Policies and guidelines: The policies and guidelines do not need to be updated.

• Trademark approval: N/A (not needed for this Change)

Upgrade/compatibility impact

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

Some packaging changes may be required for the glibc 2.34 rebase: https://sourceware.org/glibc/wiki/Release/2.33#Packaging_Changes

Some source changes may be required for gcc 11 rebase: https://gcc.gnu.org/gcc-11/changes.html All changes for gcc 11 will have been included in Fedora 34 alraedy.

There should be no need for any changes to accommodate the new GNU Binutils release.

We fully expect to fix all packaging changes in Fedora Rawhide without impact to the release.

How To Test

The GNU C compiler collection has its own testsuite which is run during the package build and examined by the gcc developers before being uploaded.

The GNU Binary Utilities has its own testsuite which is run during the package build and examined by the binutils developers before being uploaded.

The GNU C Library has its own testsuite, 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 may also run the microbenchmark to look for performance regressions.

User Experience

Users will see improved performance, many bugfixes and improvements to POSIX compliance, additional locales, etc.

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 35 cycle. In particular the glibc merge of libpthread into libc will remove the dependency in ELF binaries on libpthread, and that cleanup is valuable for consistency.

Contingency Plan

• Contingency mechanism: If glibc 2.34 provides too disruptive to compiling the distribution we could revert to 2.33, but given that Rawhide has started tracking glibc 2.34, no show-stopper problems are expected. At this point, we can still revert to upstream version 2.33 if insurmountable problems appear, but to do so may require a mass rebuild to remove new symbols from the ABI/API.
• Contingency deadline: Upstream glibc ABI freeze deadline of 2021-07-01.
• Blocks release? Yes, upgrading to the gcc point release blocks the release. Yes, upgrading to binutils 2.37 blocks the release. Yes, upgrading glibc does block the release. We should not ship without a newer binutils and glibc, there will be gcc and language features that depend on glibc being upgraded. Thus without the upgrade some features will be disabled or fall back to less optimal implementations.

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.

Release Notes

The GNU Compiler Collection version 11 is already released. See https://gcc.gnu.org/gcc-11/changes.html.

The GNU Binutils version 2.37 will be released in the middle of July and release notes will be updated at that point.

The GNU C Library version 2.34 will be released at the beginning of August 2021. 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