Bug 858752 – games-fps/quake2-icculus-0.16.1-r2 fails to compile (lto): q_shared.c:258:21: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]

• Product: Gentoo Linux
• Status: RESOLVED FIXED

[Description Agostino Sarubbo 2022-07-18 06:58:06 UTC]

https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/

Issue: games-fps/quake2-icculus-0.16.1-r2 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

[Comment 1 Agostino Sarubbo 2022-07-18 06:58:09 UTC]

Created attachment 792125 [details]
build.log

build log and emerge --info

[Comment 2 Agostino Sarubbo 2022-07-26 09:01:52 UTC]

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

[Comment 3 Larry the Git Cow 2024-05-12 22:41:16 UTC]

The bug has been closed via the following commit(s):

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=5c6938cabc43d900fa8e1090cf580b521c7e8bec

commit 5c6938cabc43d900fa8e1090cf580b521c7e8bec
Author:     Eli Schwartz <[e-mail]>
AuthorDate: 2024-05-12 17:58:38 +0000
Commit:     Sam James <[e-mail]>
CommitDate: 2024-05-12 22:38:50 +0000

    games-fps/quake2-icculus: mark as LTO-unsafe, strict-aliasing unsafe
    
    Upstream is dead since 2006, no use reporting anything. Even then, their
    last act was to convert CVS to SVN.
    
    Closes: https://bugs.gentoo.org/858752
    Signed-off-by: Eli Schwartz <[e-mail]>
    Signed-off-by: Sam James <[e-mail]>

 games-fps/quake2-icculus/quake2-icculus-0.16.1-r2.ebuild | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)