[Bug 2064539] Re: Revert back frame pointers for ppc64el (remove -fno-omit-frame-pointer)

[Frank Heimes]

Many thanks doko, the debdiff looks reasonable and good.
I did a test build (based on v1.22.6ubuntu6.1 https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/ppa/+sourcepub/16274696/+listing-archive-extra) and wasn't able to find an indication of FBs (in the debug symbols) anymore (using readelf -wi grep-ping for DW_AT_produce).
Same for LP#2064538.

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https://bugs.launchpad.net/bugs/2064539

Title:
  Revert back frame pointers for ppc64el (remove -fno-omit-frame-
  pointer)

Status in The Ubuntu-power-systems project:
  New
Status in dpkg package in Ubuntu:
  Fix Released
Status in glibc package in Ubuntu:
  New
Status in linux package in Ubuntu:
  New
Status in dpkg source package in Noble:
  New
Status in glibc source package in Noble:
  New
Status in linux source package in Noble:
  New
Status in dpkg source package in Oracular:
  Fix Released
Status in glibc source package in Oracular:
  New
Status in linux source package in Oracular:
  New

Bug description:
  Power's Linux ABIs all require an explicit call chain be stored on the call stack frames which are all accessible via the stack pointer.
  Therefore, having a (soft/simulated) frame pointer does not improve backtraces at all on Power.

  However, forcing a frame pointer via the -fno-omit-frame-pointer option negatively affects performance for multiple reasons: extra prologue/epilogue overhead and fewer shrink-wrapping opportunities.
  Given -fno-omit-frame-pointer does not provide any improvements (backtraces or otherwise) and only reduces performance, -fno-omit-frame-pointers should not be used on Power.

  SRU:

  these changes were implemented during the opening of the oracular
  series. The very same changes are backported to 24.04 LTS. These only
  affect the ppc64el and s390x architectures, for other architectures
  it's a no-change upload.

  We didn't see any fallout for these changes during the development on
  the oracular series, and therefore don't expect any fallout or
  regressions in 24.04 LTS either.

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