Bug 862909 – sci-libs/openblas-0.3.20 fails to compile (lto): xxdr.c:489:19: 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 06:58:54 UTC]

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

Issue: sci-libs/openblas-0.3.20 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 06:58:59 UTC]

Created attachment 796756 [details]
build.log.xz

build log and emerge --info (compressed because it exceeds attachment limit, use 'xzless' to read it)

[Comment 2 Larry the Git Cow 2023-07-07 00:31:55 UTC]

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

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=044b72e595e46ae602b22fc542b93008ec7ebad8

commit 044b72e595e46ae602b22fc542b93008ec7ebad8
Author:     Michael Orlitzky <[e-mail]>
AuthorDate: 2023-07-07 00:03:49 +0000
Commit:     Michael Orlitzky <[e-mail]>
CommitDate: 2023-07-07 00:28:46 +0000

    sci-libs/openblas: add 0.3.23
    
    All this really needed was a rebase of the shared-lib patch. The loong
    arch patch still applies, albeit with fuzz. The strict-aliasing warnings
    from bug 862909 also seem gone, probably as part of the underlying
    lapack upgrade.
    
    Closes: https://bugs.gentoo.org/862909
    Closes: https://bugs.gentoo.org/905277
    Signed-off-by: Michael Orlitzky <[e-mail]>

 sci-libs/openblas/Manifest                         |   1 +
 .../files/openblas-0.3.23-shared-blas-lapack.patch |  40 +++++
 sci-libs/openblas/openblas-0.3.23.ebuild           | 196 +++++++++++++++++++++
 3 files changed, 237 insertions(+)