F38 proposal: GNU Toolchain Update (gcc 13.0, binutils 2.39, glibc 2.37, gdb 12.1) (System-Wide Change proposal)

[Ben Cotton]

https://fedoraproject.org/wiki/Changes/GNUToolchainF38

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 38 GNU Toolchain to gcc 13.0, binutils 2.39, and glibc 2.37.

The existing gdb 12.1 will be used as-is.

The set of core GNU Toolchain packages for Fedora 38 are as follows:

* GNU C Compiler 13.0
** Associated runtimes for C++ (libstdc++), Go (gccgo), OpenMP (gomp),
Fortran (gfortran), D (phobos), Objective C/C++.
* GNU Binary Utilities 2.39
* GNU C Library 2.37
* GNU Debugger 12.1 (immediately available in Fedora 37)

The gcc 13.0 change will be tracked in this top-level GNU Toolchain
system-wide update.

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

The glibc 2.37 change will be tracked in this top-level GNU Toolchain
system-wide update.

== Owner ==
* Name: [[User:codonell|Carlos O'Donell]]
* Email: [e-mail]

== 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 13.0, after
the Fedora 38 release. It will contain many new features, documented
here: https://gcc.gnu.org/gcc-13/changes.html. The latest release
candidate for gcc 13 will be included in Fedora 38 and will be updated
when released.

The GNU Binutils version 2.39 was released before Fedora 38; and we
have already been using this version of binutils in Fedora Rawhide
successfully to build the distribution for the last 4 months. Given
the present schedule for Fedora 38 we will continue to use Binutils
2.39.

The GNU C Library version 2.37 is expected to be release before Fedora
38; we have started closely tracking the glibc 2.37 development code
in Fedora Rawhide and are addressing any issues as they arise. Given
the present schedule Fedora 38 will branch after the release of glibc
2.37. However, the mass rebuild schedule means Fedora 38 will mass
rebuild (if required) before the final release of glibc 2.37, but
after the ABI is frozen.

The GNU Debugger version 12.1 was released before Fedora 38; and we
plan to continue to use this version of the debugger.

== 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 38 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;
[https://pagure.io/releng/issue/XX #XX]
** Filed after approval.

* 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 the gcc 13 update. Please
refer to the latest changes here:
https://gcc.gnu.org/gcc-13/changes.html

Any source level changes required for glibc 2.37 will be noted here:
https://sourceware.org/glibc/wiki/Release/2.37#Packaging_Changes

== How To Test ==
The GNU Compiler Collection has its own testsuite which is run during
the package build and examined by the gcc 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 we may also run the
microbenchmark to look for performance regressions.

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

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

== User Experience ==
Fedora developers as well as developers using the distribution will be
able to use and develop using the new features offered by the updated
components. Developers will need to enable specific compiler features
as required e.g. '-mcpu=neoverse-v2'.

== 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 38 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 2.37 proves too disruptive to
compiling the distribution we could revert to 2.36, but given that
Rawhide has started tracking glibc 2.37, no show-stopper problems are
expected.  At this point we can still revert to upstream version 2.36
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 2.39 proves too
distruptive to assembling and linking the distribution we could revert
to 2.38, but given that Rawhide is using 2.39, 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 13 proves too disruptive to
compiling the distribution we could revert to gcc 12.

* Contingency mechanism for gdb: The gdb 12.1 release is already in
all the Fedora releases and it would not be reverted. If any gcc,
glibc or binutils changes cause gdb to fail then that would need to be
reviewed on a case-by-case basis.

* Contingency deadline: Fedora mass rebuild on 2023-01-18.
* Blocks release?
** Yes, upgrading to gcc 13.0 does block the release.
** Yes, upgrading to binutils 2.39 does block the release.
** Yes, upgrading to glibc 2.37 does block the release.
** No, upgrading to gdb 12.1 does block the release (already released).

== 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 ==
<!-- Use this text for GCC updates: -->

See https://gcc.gnu.org/gcc-13/changes.html for the GNU Compiler
Collection version 13 release notes.

<!-- Use this text for GLIBC updates: -->
The GNU C Library version 2.37 will be released at the beginning of
February 2023. 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 2.39 was released August 2022. The
current release notes will be sent to the developer mailing list:
https://sourceware.org/pipermail/binutils/2022-August/122246.html.