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Bug 858749 - games-fps/gzdoom-4.8.2 fails to compile (lto): xbrz.cpp:720:72: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
Summary: games-fps/gzdoom-4.8.2 fails to compile (lto): xbrz.cpp:720:72: error: derefe...
Status: RESOLVED FIXED
Alias: None
Product: Gentoo Linux
Classification: Unclassified
Component: Current packages (show other bugs)
Hardware: All Linux
: Normal normal (vote)
Assignee: William Breathitt Gray
URL:
Whiteboard:
Keywords: PullRequest
Depends on: 858374
Blocks: lto
  Show dependency tree
 
Reported: 2022-07-18 06:58 UTC by Agostino Sarubbo
Modified: 2022-08-04 07:12 UTC (History)
2 users (show)

See Also:
Package list:
Runtime testing required: ---


Attachments
build.log (build.log,428.92 KB, text/plain)
2022-07-18 06:58 UTC, Agostino Sarubbo
Details

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Description Agostino Sarubbo gentoo-dev 2022-07-18 06:58:00 UTC
https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/

Issue: games-fps/gzdoom-4.8.2 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 2022-07-18 06:58:03 UTC
Created attachment 792122 [details]
build.log

build log and emerge --info
Comment 2 Agostino Sarubbo gentoo-dev 2022-07-18 06:58:05 UTC
Error(s) that match a know pattern in addition to what has been reported in the summary:


FAILED: src/CMakeFiles/zdoom.dir/common/textures/hires/xbr/xbrz.cpp.o 
/var/tmp/portage/games-fps/gzdoom-4.8.2/work/gzdoom-g4.8.2/src/common/textures/hires/xbr/xbrz.cpp:720:72: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
Comment 3 William Breathitt Gray 2022-07-22 16:55:58 UTC
Upstream bug issue filed: https://github.com/coelckers/gzdoom/issues/1673
Comment 4 Agostino Sarubbo gentoo-dev 2022-07-26 09:01:51 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 5 Larry the Git Cow gentoo-dev 2022-08-04 07:12:30 UTC
The bug has been closed via the following commit(s):

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=a19c006e1cf58d10c82fe9a944b490780cbddcc0

commit a19c006e1cf58d10c82fe9a944b490780cbddcc0
Author:     William Breathitt Gray <vilhelm.gray@gmail.com>
AuthorDate: 2022-07-22 20:36:23 +0000
Commit:     Joonas Niilola <juippis@gentoo.org>
CommitDate: 2022-08-04 07:04:43 +0000

    games-fps/gzdoom: Filter LTO and disable strict aliasing
    
    Closes: https://bugs.gentoo.org/858749
    Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
    Closes: https://github.com/gentoo/gentoo/pull/26525
    Signed-off-by: Joonas Niilola <juippis@gentoo.org>

 games-fps/gzdoom/gzdoom-4.8.2.ebuild | 4 ++++
 1 file changed, 4 insertions(+)