[Bug 2025142] Re: SRU: build isl with the standard baseline

[Steve Langasek]

I have tried to reproduce this bug in qemu, as Matthias has suggested
that initialization of the library by calling gcc should be enough to
trigger the SIGILL.

I have tried using the 'Conroe' CPU emulation in qemu from Ubuntu 23.04
Desktop live environment, and 'gcc --help' succeeds.

I have tried booting lunar on a Pentium 3 machine type, and it fails to
boot to grub under UEFI, so that's an interesting data point.


Switching it to BIOS boot gets me a successful boot to grub, but cannot boot the kernel.

I haven't been able to identify an emulation target in between these
from the list of qemu targets, so I guess we don't actually have a test
case.

Based on feedback out of band from Matthias that this is not a
significant enough bug to warrant him investing further time into
developing a test case, I am going to go ahead and reject the uploads.

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https://bugs.launchpad.net/bugs/2025142

Title:
  SRU: build isl with the standard baseline

Status in isl package in Ubuntu:
  Fix Released
Status in isl source package in Jammy:
  Won't Fix
Status in isl source package in Kinetic:
  Won't Fix
Status in isl source package in Lunar:
  Won't Fix

Bug description:
  by default, isl picks up the current processor and optimizes the build
  for that processor. That's not what we want. Configure isl --without-
  gcc-arch instead.

  [ Impact ]

  GCC (linked to libisl) aborts with an illegal instruction on older
  processors.

  Configuring --without-gcc-arch makes isl (and gcc) to work on all
  processors again.

  [ Test plan ]

  Hard to test, because we don't have older processors available. Just
  rely to the build logs, that no explicit -march option is passed in
  the compiler flags.

  [ Where problems could occur ]

  The regression potential is small, isl is only used for the graphite
  optimizations in GCC, which are not used by default.

  isl might become a bit slower when restricted to the standard
  baseline.

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