https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/ Issue: app-editors/emacs-18.59-r14 fails to compile (lto). Discovered on: amd64 (internal ref: lto_tinderbox) NOTE: This machine uses lto with CFLAGS=-flto -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing
Created attachment 787682 [details] build.log build log and emerge --info
For older Emacs, let's just use -fno-strict-aliasing.
I must admit that I'm getting tired of bugs of this type. It's a strange idea to compile emacs:18 with that combination of CFLAGS. Also this isn't a real issue, otherwise users would have reported it earlier. Maybe time to retire slot 18 (as well as 23 to 26), or move it to the emacs overlay?
The bug has been referenced in the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=f32b8cd1cdedb9e74ecbd8a07244eaf5250a9e04 commit f32b8cd1cdedb9e74ecbd8a07244eaf5250a9e04 Author: Ulrich Müller <ulm@gentoo.org> AuthorDate: 2022-06-26 10:33:19 +0000 Commit: Ulrich Müller <ulm@gentoo.org> CommitDate: 2022-06-26 10:34:15 +0000 app-editors/emacs: Compile Emacs 18 with -fno-strict-aliasing Bug: https://bugs.gentoo.org/854360 Suggested-by: Sam James <sam@gentoo.org> Signed-off-by: Ulrich Müller <ulm@gentoo.org> app-editors/emacs/emacs-18.59-r14.ebuild | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
Here is a bit of explanation: -Werror=lto-type-mismatch: User to find possible runtime issues in packages. It likely means the package is unsafe to build & use with LTO. For projects using the same identifier but with different types across different files, they must be fixed to be consistent across the codebase. -Werror=odr: Used to find possible runtime issues in packages. These bugs are a problem anyway but may be even worse when combined with LTO. C++ code must comply with the One Definition Rule (ODR) - see https://en.cppreference.com/w/cpp/language/definition#One_Definition_Rule. -Werror=strict-aliasing: Used to find possible runtime issues in packages. These bugs are a problem anyway but may be even worse when combined with LTO. Workarounds: - If upstream is friendly and still active, file a bug upstream. For emulators, codecs, games, or multimedia packages, it may be worth just applying a workaround instead, as upstreams sometimes aren't receptive to these bugs (VALID FOR ALL). - Use the new 'filter-lto' from flag-o-matic.eclass as it's likely to be unsafe with LTO (VALID FOR lto-type-mismatch - odr). - Fix it yourself if interested, of course (VALID FOR ALL). - Append-flags -fno-strict-aliasing (VALID FOR strict-aliasing). - Use memcpy() but a union is sometimes suitable too (VALID FOR strict-aliasing). - -fstrict-aliasing is implied by -O2, so this must be addressed in some form (VALID FOR strict-aliasing). See also: https://marc.info/?l=gentoo-dev&m=165639574126280&w=2
