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Bug 858638

Summary: games-emulation/dosbox-0.75_pre4302 fails to compile (lto): dos_inc.h:253:33: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
Product: Gentoo Linux Reporter: Agostino Sarubbo <ago>
Component: Current packagesAssignee: Gentoo Games <games>
Status: RESOLVED FIXED    
Severity: normal CC: andrius, eschwartz, wine
Priority: Normal    
Version: unspecified   
Hardware: All   
OS: Linux   
Whiteboard:
Package list:
Runtime testing required: ---
Bug Depends on:    
Bug Blocks: 618550    
Attachments: build.log

Description Agostino Sarubbo gentoo-dev 2022-07-17 17:55:23 UTC
https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/

Issue: games-emulation/dosbox-0.75_pre4302 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 gentoo-dev 2022-07-17 17:55:26 UTC
Created attachment 791987 [details]
build.log

build log and emerge --info
Comment 2 Agostino Sarubbo gentoo-dev 2022-07-26 09:01:41 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 4 Eli Schwartz gentoo-dev 2024-08-05 04:33:08 UTC
Unfortunately not. dosbox and dosbox-staging are run independently -- moreover, this error is a strict-aliasing bug, not an ODR violation, and triggers much earlier.
Comment 5 Larry the Git Cow gentoo-dev 2024-08-06 00:20:04 UTC
The bug has been closed via the following commit(s):

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=bf241a4260954afb732b4600e8ad82e744135833

commit bf241a4260954afb732b4600e8ad82e744135833
Author:     Eli Schwartz <eschwartz@gentoo.org>
AuthorDate: 2024-08-05 04:45:07 +0000
Commit:     Eli Schwartz <eschwartz@gentoo.org>
CommitDate: 2024-08-06 00:18:30 +0000

    games-emulation/dosbox: mark as LTO-unsafe, strict-aliasing unsafe
    
    Closes: https://bugs.gentoo.org/858638
    Signed-off-by: Eli Schwartz <eschwartz@gentoo.org>

 games-emulation/dosbox/dosbox-0.75_pre4302.ebuild | 8 ++++++++
 games-emulation/dosbox/dosbox-9999.ebuild         | 8 ++++++++
 2 files changed, 16 insertions(+)