Latest revision as of 17:13, 2 October 2024

LLVM 19

Summary

Update all llvm sub-projects in Fedora Linux to version 19.

Owner

Name: Tom Stellard
Email: <tstellar@redhat.com>

Current status

Targeted release: Fedora Linux 41
Last updated: 2024-10-02
Announced
Discussion thread
FESCo issue: #3220
Tracker bug: #2293629
Release notes tracker: #114

Detailed Description

All llvm sub-projects in Fedora will be updated to version 19, and there will be a soname version change for the llvm libraries. Compatibility packages clang18, llvm18, lld18, compiler-rt18, and libomp18 will be added to ensure that packages that currently depend on clang and llvm version 18 libraries will continue to work. We may add other compatibility packages too if they're determined to be necessary to maintain functionality in other RPMS that use llvm/clang. Any compatibility packages we add for Fedora 41 will be retired or orphaned before the Fedora 42 branch date. As stated in the LLVM-18 change proposal, we plan to retire or orphan these older compatibility packages prior to the Fedora 41 branch date:

llvm17
clang17
lld17
compiler-rt17
libomp17

Other notable changes:

Build compat packages (e.g. llvm18) as early as possible. When we package a new major release of llvm, we create a compat package so that packages that aren't compatible with the new version can still use the old version. In the past, we've waited to introduce the compat packages until the new version of LLVM was ready (typically during the Beta Freeze). However, this proved to be an issue this release for packages the were ready to switch to the compat packages early in the release cycle, but then had to wait for Beta freeze.

Spec file merge. We plan to retire the clang, compiler-rt, lld and libomp packages and merge them in with llvm and have them be sub-packages of the llvm package. All these packages have their sources in the same upstream git repository and use the same versioning. This change will allow us to use the build configuration recommended by upstream and also make it possible to optimize the packages using Profile-Guided Optimizations (PGO). It's possible that in future releases (f42+), we may decided to merge more packages in with llvm too.

Fat LTO. All RPMS built with clang will default to using the -ffat-lto option. Fat LTO is a feature that allows the compiler to produce libraries that contain LTO bitcode along side the traditional ELF binary code so that the libraries can be linked in both LTO mode and non-LTO mode. gcc also supports this feature and has it enabled in Fedora. In Fedora 40 and older, with LTO enabled, clang produces binaries with only LTO bitcode, so we need to run a post-processing script (brp-llvm-compile-to-elf) on the libraries to convert them to ELF code so they can be used by other packages. Enabling Fat LTO will allow us to remove this script and simplify the build process. We originally proposed this feature for Fedora 40, but it was not ready in time.

Planned Schedule

Our plan is to push 19.1.0-rc3 into Fedora 41 as a Beta Freeze exception. Updates after 19.1.0-rc3 will generally be very small and can be done after the Beta Freeze is over. If we are late packaging releases after 19.1.0-rc3, we will not ask for a Final Freeze exception, unless they contain a fix for a critical release blocking bug.

We are not planning to push 19.1.0-rc1 into rawhide because the library ABI is not stabilized at that point. Typically, the ABI stabilizes after -rc3, but there are no guarantees from upstream about this. Given the history of minimal ABI changes after -rc3, we feel like it's safe to push -rc3 into rawhide and Fedora 41. The worst case scenario would be an ABI change in -rc4 or the final release that would force us to patch LLVM to maintain compatibility with the -rc3 ABI. This scenario would not require rebuilding LLVM library users in Fedora, so it would merely be a self-contained change to LLVM.

Important Dates

Dates may change depending on circumstances.

Jun 4: Build llvm18, clang18, lld18, compiler-rt18, and lld18 compat packages in rawhide.
July 26: Begin building LLVM 19.1.0-rc1 in COPR.
Aug 6: Begin building LLVM 19.1.0-rc2 in COPR.
Aug 6: Fedora f41 branches created.
Aug 20: Begin building LLVM 19.1.0-rc3 in Rawhide and f41 side-tags.
Aug 20: Fedora f41 Beta Freeze
Aug 20-> Sep 10: Request Beta Freeze Exception and push 19.1.0-rc3 into f41 stable.
Sep 3: Begin building LLVM 19.1.0-rc4 in Rawhide side-tag.
Sep 17: Begin building LLVM 19.1.0 in Rawhide and f41 side-tags.
Sep 17 -> Oct 1: Push 19.1.0 into f41 stable.
Oct 1: Fedora f41 Final Freeze.

Feedback

Benefit to Fedora

New features and bug fixes provided by the latest version of LLVM.

Scope

Proposal owners:
- Review existing llvm and clang compatibility packages and orphan any packages that are no longer used.
- Build and test early release candidates of LLVM 19 in COPR.

Other developers:
- Fix build issues found with LLVM-19 or switch their package to use the llvm18 compat libs. The LLVM team will not block Bodhi updates on dependent packages that fail to build or run with LLVM-19. There should be around 6-8 weeks between when -rc1 lands in the koji side-tag and the Final Freeze for package maintainers to fix issues uncovered with the LLVM-19 update.

Release engineering: [1]

Policies and guidelines: N/A (not needed for this Change)

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

Alignment with the Fedora Strategy:

Upgrade/compatibility impact

This change should not impact upgrades.

Early Testing (Optional)

Do you require 'QA Blueprint' support? Y/N

How To Test

The CI tests for the llvm sub-packages in Fedora will be used to catch regressions that might be potentially introduced by the update to LLVM 19.

User Experience

Dependencies

Packages that depend on one of the llvm packages will need to be updated to work with LLVM19 or will need to switch to using one of the llvm18 compat packages.

Contingency Plan

Contingency mechanism: (What to do? Who will do it?)

If there are major problems with LLVM 19, the compatibility package provide a way for other packages to continue using LLVM 18.

Contingency deadline:Final Freeze
Blocks release? No (not a System Wide Change), Yes/No

Documentation

LLVM sub-projects in Fedora have been updated to version 19:

llvm (now includes clang, lld, compiler-rt, libomp)
lldb
llvm-test-suite
libcxx
python-lit
flang
mlir
polly
libclc
llvm-bolt

Release Notes

@@ Line 3: / Line 3: @@
 = LLVM 19 <!-- The name of your change proposal --> =
-{{Change_Proposal_Banner}}
 == Summary ==
@@ Line 22: / Line 21: @@
 == Current status ==
-[[Category:ChangePageIncomplete]]
+[[Category:ChangeAcceptedF42]]
 <!-- When your change proposal page is completed and ready for review and announcement -->
 <!-- remove Category:ChangePageIncomplete and change it to Category:ChangeReadyForWrangler -->
@@ Line 31: / Line 30: @@
 <!--[[Category:SelfContainedChange]]-->
 [[Category:SystemWideChange]]
-* Targeted release: [https://docs.fedoraproject.org/en-US/releases/f<VERSION>/ Fedora Linux <VERSION>]
+* Targeted release: [https://docs.fedoraproject.org/en-US/releases/f42/ Fedora Linux 41]
 * Last updated: <!-- this is an automatic macro — you don't need to change this line -->  {{REVISIONYEAR}}-{{REVISIONMONTH}}-{{REVISIONDAY2}}
 <!-- After the change proposal is accepted by FESCo, tracking bug is created in Bugzilla and linked to this page
@@ Line 39: / Line 38: @@
 ON_QA -> change is fully code complete
 -->
-* [Announced]
+* [https://lists.fedoraproject.org/archives/list/devel-announce@lists.fedoraproject.org/thread/ZJAFWUAUFOQCOZOL7UBGH6PPA5KGPQTR/ Announced]
-* [<will be assigned by the Wrangler> Discussion thread]
+* [https://discussion.fedoraproject.org/t/f41-change-proposal-llvm-19-system-wide/118552 Discussion thread]
-* FESCo issue: <will be assigned by the Wrangler>
+* FESCo issue: [https://pagure.io/fesco/issue/3220 #3220]
-* Tracker bug: <will be assigned by the Wrangler>
+* Tracker bug: [https://bugzilla.redhat.com/show_bug.cgi?id=2293629 #2293629]
-* Release notes tracker: <will be assigned by the Wrangler>
+* Release notes tracker: [https://gitlab.com/fedora/docs/fedora-linux-documentation/release-notes/-/issues/114 #114]
 == Detailed Description ==
@@ Line 60: / Line 59: @@
 * '''Build compat packages (e.g. llvm18) as early as possible.'''  When we package a new major release of llvm, we create a compat package so that packages that aren't compatible with the new version can still use the old version.  In the past, we've waited to introduce the compat packages until the new version of LLVM was ready (typically during the Beta Freeze).  However, this proved to be an issue this release for packages the were ready to switch to the compat packages early in the release cycle, but then had to wait for Beta freeze.
-* '''Spec file merge.'''  We plan to merge the clang, compiler-rt, lld and libomp packages in with llvm and have them be sub-packages of the llvm package.  All these packages have their sources in the same upstream git repository and use the same versioning.  This change will allow us to use the build configuration recommended by upstream and also make it possible to optimize the packages using Profile-Guided Optimizations (PGO).
+* '''Spec file merge.'''  We plan to retire the clang, compiler-rt, lld and libomp packages and merge them in with llvm and have them be sub-packages of the llvm package.  All these packages have their sources in the same upstream git repository and use the same versioning.  This change will allow us to use the build configuration recommended by upstream and also make it possible to optimize the packages using Profile-Guided Optimizations (PGO).  It's possible that in future releases (f42+), we may decided to merge more packages in with llvm too.
 * '''Fat LTO'''. All RPMS built with clang will default to using the -ffat-lto option.  Fat LTO is a feature that allows the compiler to produce libraries that contain LTO bitcode along side the traditional ELF binary code so that the libraries can be linked in both LTO mode and non-LTO mode. gcc also supports this feature and has it enabled in Fedora. In Fedora 40 and older, with LTO enabled, clang produces binaries with only LTO bitcode, so we need to run a post-processing script (brp-llvm-compile-to-elf) on the libraries to convert them to ELF code so they can be used by other packages. Enabling Fat LTO will allow us to remove this script and simplify the build process.  We originally proposed this feature for Fedora 40, but it was not ready in time.
@@ Line 123: / Line 122: @@
 <!-- What work do the feature owners have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
 ** Review existing llvm and clang compatibility packages and orphan any packages that are no longer used.
-** Build and test early release candidates of LLVM 18 in COPR.
+** Build and test early release candidates of LLVM 19 in COPR.
 * Other developers: <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 <!-- What work do other developers have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
-** Fix build issues found with LLVM-18 or switch their package to use the llvm17 compat libs.  The LLVM team will not block Bodhi updates on dependent packages that fail to build or run with LLVM-18.  There should be around 6-8 weeks between when -rc1 lands in the koji side-tag and the Final Freeze for package maintainers to fix issues uncovered with the LLVM-18 update.
+** Fix build issues found with LLVM-19 or switch their package to use the llvm18 compat libs.  The LLVM team will not block Bodhi updates on dependent packages that fail to build or run with LLVM-19.  There should be around 6-8 weeks between when -rc1 lands in the koji side-tag and the Final Freeze for package maintainers to fix issues uncovered with the LLVM-19 update.
-* Release engineering: [https://pagure.io/releng/issues #Releng issue number] <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
+* Release engineering: [https://pagure.io/releng/issue/12118] <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 <!-- Does this feature require coordination with release engineering (e.g. changes to installer image generation or update package delivery)?  Is a mass rebuild required?  include a link to the releng issue.
 The issue is required to be filed prior to feature submission, to ensure that someone is on board to do any process development work and testing and that all changes make it into the pipeline; a bullet point in a change is not sufficient communication -->
@@ Line 195: / Line 194: @@
 <!-- When is the last time the contingency mechanism can be put in place?  This will typically be the beta freeze. -->
-If there are major problems with LLVM 18, the compatibility package provide a way for other packages to continue using LLVM 17.
+If there are major problems with LLVM 19, the compatibility package provide a way for other packages to continue using LLVM 18.
 * Contingency deadline:Final Freeze  <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
@@ Line 207: / Line 206: @@
 LLVM sub-projects in Fedora have been updated to version 19:
-* llvm
+* llvm (now includes clang, lld, compiler-rt, libomp)
-* clang
-* lld
 * lldb
-* compiler-rt
-* libomp
 * llvm-test-suite
 * libcxx

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