Bug 862903 – sci-libs/mumps-5.3.5-r1 fails to compile (lto): mumps_size.c:24:8: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]

• Product: Gentoo Linux
• Status: RESOLVED FIXED

[Description Agostino Sarubbo 2022-08-02 06:57:32 UTC]

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

Issue: sci-libs/mumps-5.3.5-r1 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

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 1 Agostino Sarubbo 2022-08-02 06:57:34 UTC]

Created attachment 796750 [details]
build.log

build log and emerge --info

[Comment 2 Larry the Git Cow 2024-03-21 05:58:44 UTC]

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

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=3b05cbc43c32d8c519df31a6ccabd17ebd0d6d19

commit 3b05cbc43c32d8c519df31a6ccabd17ebd0d6d19
Author:     Eli Schwartz <[e-mail]>
AuthorDate: 2024-03-21 03:05:50 +0000
Commit:     Sam James <[e-mail]>
CommitDate: 2024-03-21 05:57:37 +0000

    sci-libs/mumps: mark as LTO-unsafe, strict-aliasing unsafe
    
    I would like to report this upstream. However, the only contact method
    is their mailing list. And their mailing list may or may not work -- I
    find it hard to tell because I've never seen the interface before, but
    it is mostly in French and the bit that I recognized doesn't seem to
    have working links to e.g. the archive.
    
    Closes: https://bugs.gentoo.org/862903
    Signed-off-by: Eli Schwartz <[e-mail]>
    Signed-off-by: Sam James <[e-mail]>

 sci-libs/mumps/mumps-5.3.5-r1.ebuild | 10 ++++++++++
 1 file changed, 10 insertions(+)