Bug 863899 – sys-fs/fuse-2.9.9-r1 fails to compile (lto): fuse_session.c:211:25: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]

• Product: Gentoo Linux
• Status: RESOLVED FIXED

[Description Agostino Sarubbo 2022-08-06 06:21:46 UTC]

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

Issue: sys-fs/fuse-2.9.9-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 2022-08-06 06:21:48 UTC]

Created attachment 798142 [details]
build.log

build log and emerge --info

[Comment 2 Larry the Git Cow 2022-08-15 00:56:54 UTC]

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

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=57b441c2eded3f8a1574203772f9a8395f250c55

commit 57b441c2eded3f8a1574203772f9a8395f250c55
Author:     Sam James <[e-mail]>
AuthorDate: 2022-08-15 00:55:55 +0000
Commit:     Sam James <[e-mail]>
CommitDate: 2022-08-15 00:56:01 +0000

    sys-fs/fuse: filter LTO for :0
    
    It's not really maintained anymore upstream so we should focus efforts on 3.
    
    Closes: https://bugs.gentoo.org/863899
    Signed-off-by: Sam James <[e-mail]>

 sys-fs/fuse/fuse-2.9.9-r1.ebuild | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

[Comment 3 Larry the Git Cow 2022-08-15 01:20:31 UTC]

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

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=fd285c34286e78b1e784807e43705447171ba555

commit fd285c34286e78b1e784807e43705447171ba555
Author:     Sam James <[e-mail]>
AuthorDate: 2022-08-15 01:18:15 +0000
Commit:     Sam James <[e-mail]>
CommitDate: 2022-08-15 01:20:18 +0000

    sys-fs/fuse: disable strict aliasing too for :0
    
    Got distracted by the filter-flags -flto -> filter-lto change.
    
    Revbump given I don't expect any new release for :0.
    
    Closes: https://bugs.gentoo.org/863899
    Fixes: 57b441c2eded3f8a1574203772f9a8395f250c55
    Signed-off-by: Sam James <[e-mail]>

 sys-fs/fuse/fuse-2.9.9-r2.ebuild | 80 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)