[Bug 2064538] Please test proposed package

[Łukasz Zemczak]

Hello Frank, or anyone else affected,

Accepted dpkg into noble-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/dpkg/1.22.6ubuntu6.1
in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
noble to verification-done-noble. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-noble. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

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https://bugs.launchpad.net/bugs/2064538

Title:
  Revert back frame pointers for s390x (remove -fno-omit-frame-pointer
  but use -mbackchain)

Status in Ubuntu on IBM z Systems:
  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:
  Fix Committed
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:
  The preferred way of doing stack unwinding on Linux on Z is via dwarf call frame information.
  In absence of a dwarf unwinder (as in the Linux kernel) a stack chain can be maintained at runtime in addition to the dwarf unwinding information.
  This allows for simple backtrace implementations, but imposes a small runtime overhead. For this to work, all code that might be part of backtrace must be built with the -mbackchain GCC option.

  The -fno-omit-framepointer switch is neither necessary nor helpful in this context.
  Having a (soft/simulated) frame pointer does not improve backtraces at all on IBM Z.
  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 IBM Z.

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