* Miro Hrončok: > * #2923 Re-vote for Change proposal: Add -fno-omit-frame-pointer to > default (mhroncok, 17:06:26) > * LINK: > https://src.fedoraproject.org/rpms/redhat-rpm-config/pull-request/230 > is the implementation (davide, 17:13:47) > * AGREED: APPROVED (+6,1,-1) This Change is implemented for Fedora > Linux 38 and we evaluate whether to retain it by Fedora Linux 40. > This Change must be implemented in a manner which packages are able > to trivially opt-out of retaining frame pointers during compilation > so that packages that take larger performance hits can easily > revert. (mhroncok, 17:20:38) > * Change owners please coordinate the change with the Python > Maintainers before changing the defaults (mhroncok, 17:21:20) The change as voted simply does not work at a technical level because -mno-omit-leaf-frame-pointer is an architecture-specific GCC option that is not available on all Fedora architectures. I don't think -fno-omit-frame-pointer is well-exercised on s390x, so I wouldn't want to use it there, either. Is it safe to assume this change (as voted) is actually intended for x86_64 only, in both directions? Specifically, that opting out will *not* disable frame pointers on aarch64 and ppc64le (where it would result in an ABI break)? We should not ask package maintainers to debug i686 build failures related to inline assembly and register shortage. (On i686, it's impossible to make certain system calls while preserving a frame pointer.) As far as I understand it, building i686 with frame pointers isn't in scope for the change, either, because it does not further its goals. Regarding leaf functions, on typical workloads, a significant fraction of the profiling samples will be in glibc string functions, which do not have frame pointers. So any profiler has to cope with leaf functions with frame pointers anyway. As a result, do we really need the -mno-omit-leaf-frame-pointer option? On aarch64, we should not use -mno-omit-leaf-frame-pointer because there is no skipped frame problem with backtraces: the link register (x30) can be read directly even in leaf functions. The ABI only mandates frame pointers for non-leaf functions. On ppc64le, GCC does not even support -mno-omit-leaf-frame-pointer. This is why I think the change is implicitly just for x86_64. Does anybody know how this change invalidates Fedora binaries as a reference for DWARF performance work? Do the generated .eh_frame data change materially once frame pointers are in use? Thanks, Florian _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue
