Frank, can you help me in writing up some test cases for both of these
bugs? SO that we have formally a test case someone can follow or at
least understand. Thanks!
** Changed in: dpkg (Ubuntu Noble)
Status: New => Fix Committed
** Tags added: verification-needed verification-needed-noble
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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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