https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/ Issue: games-emulation/np2kai-22_p20210211 fails to compile (lto). Discovered on: amd64 (internal ref: guru_tinderbox) NOTE: This machine uses lto with CFLAGS=-flto -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing
Created attachment 793067 [details] build.log build log and emerge --info
Error(s) that match a know pattern in addition to what has been reported in the summary: -- Could NOT find SDL (missing: SDL_LIBRARY SDL_INCLUDE_DIR) -- Could NOT find SDL_mixer (missing: SDL_MIXER_LIBRARIES SDL_MIXER_INCLUDE_DIRS) -- Could NOT find SDL_ttf (missing: SDL_TTF_LIBRARIES SDL_TTF_INCLUDE_DIRS) FAILED: CMakeFiles/sdlnp2kai.dir/io/egc.c.o fatal: not a git repository (or any parent up to mount point /var/tmp) /var/tmp/portage/games-emulation/np2kai-22_p20210211/work/NP2kai-3e8fedc7c1c6f68faa26589187512474a766ee9e/io/egc.c:60:41: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
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
