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

[Chris Halse Rogers]

> - userspace code is unaffected

Aha! This was not obvious to me from the bug. With that additional bit
of context, there is indeed nothing to worry about.

> Also explicitely at
https://wiki.ubuntu.com/StableReleaseUpdates#Newer_Releases

Hm. We *were* worried when we wrote that that it would be interpreted as
"as soon as N+1 is released, you no longer need to fix (non-LTS) N"
which was not our intent. The publicised policy is that non-LTS releases
have a 9 month support lifespan; if *everyone* skips uploading fixes to
a non-LTS release as soon it is superseded then that's just 6 months.

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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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