[Bug 2002429] Re: Patch needs to be removed ("debian/patches/gcc-ibmz-plt-revert.diff: Revert PLT changes from the gcc-11 branch")

[Dimitri John Ledkov]

On Thu, 18 May 2023, 01:25 Chris Halse Rogers, <2002429 at bugs.launchpad.net>
wrote:

> But this is not just patching the compiler used to build the kernel,
> it's patching the compiler available to everyone in the gcc-11 package?
> I may not have the full context to the fix, but this looks like it
> doesn't *just* change codegen for the kernel, right?
>
> It's fine for kinetic to be deprioritised - gcc-11 is in universe rather
> than main there so we've already communicated a lower support level, and
> kinetic is already superseded - but I think we've decided that while
> it's OK to skip intermediate releases we want that to be an actively
> documented choice rather than just silently failing to fix.
>

This is an active choice.
No packages in kinetic+ use gcc-11.
gcc-11 in kinetic+ exists to apply and test fixes for SRUs to jammy where
it is the default compiler; as well as to compile EFI code that is copied
back (grub2-unsigned).

Furthermore this fix insofar affects kernel compiled kernel, thus yes this
is fixing kernel compiler codepath in jammy only, as kinetic+ is fixed
(specifically kinetic+ kernels require gcc-12 due to kconfig hardening
choices).



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> Title:
>   Patch needs to be removed ("debian/patches/gcc-ibmz-plt-revert.diff:
>   Revert PLT changes from the gcc-11 branch")
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https://bugs.launchpad.net/bugs/2002429

Title:
  Patch needs to be removed ("debian/patches/gcc-ibmz-plt-revert.diff:
  Revert PLT changes from the gcc-11 branch")

Status in Ubuntu on IBM z Systems:
  New
Status in gcc-11 package in Ubuntu:
  Fix Released
Status in gcc-11-cross package in Ubuntu:
  New
Status in gcc-11-cross-ports package in Ubuntu:
  New
Status in gcc-11 source package in Jammy:
  Fix Committed
Status in gcc-11-cross source package in Jammy:
  Fix Committed
Status in gcc-11-cross-ports source package in Jammy:
  Fix Committed
Status in gcc-11 source package in Kinetic:
  New
Status in gcc-11 source package in Lunar:
  Fix Released
Status in gcc-11 package in Debian:
  Fix Released

Bug description:
  [ Impact ]

   * Bug #1954676 (https://bugs.launchpad.net/bugs/1954676) was opened
  because of kernel soft lockup issues with Jammy 5.15. A temporary
  patch to gcc-11 was identified and released under debian/patches/gcc-
  ibmz-plt-revert.diff, which reverted gcc commit 0990d93 ("IBM Z: Use
  @PLT symbols for local functions in 64-bit mode"). An eventual fix to
  the kernel lockup was released under the upstream Linux kernel, commit
  f3b7e73b2c66.

   * To this end, the debian/patches/gcc-ibmz-plt-revert.diff patch
  should be removed from gcc-11 as it presents issues with object file
  symbols. An attempt at this is in my PPA -
  https://launchpad.net/~john-cabaj/+archive/ubuntu/gcc-11). This
  allowed me to get past my issues with the object file symbols.

  [ Test Plan ]

   * use kpatch-build testcases to build and load a livepatch on s390x
  kernel built with gcc-11

   * it should be successful

  [ Where problems could occur ]

   * Whilst the kernel issues was worked-around by reverting compiler
  changes, the actual issue was in the kernel code; which has since been
  fixed. In ubuntu the kernel has been fixed since Ubuntu-5.15.0-20.20

  [ Other Info ]
   
   * A bit sad that this was not detected earlier, and compiler fixed up earlier.

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