Bug 864535

Summary:	x11-libs/neXtaw-0.15.1-r3 fails to compile (lto): Scrollbar.c:1389:40: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
Product:	Gentoo Linux	Reporter:	Agostino Sarubbo <ago>
Component:	Current packages	Assignee:	No maintainer - Look at https://wiki.gentoo.org/wiki/Project:Proxy_Maintainers if you want to take care of it <maintainer-needed>
Status:	RESOLVED FIXED
Severity:	normal
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

2022-08-09 07:08:22 UTC

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

Issue: x11-libs/neXtaw-0.15.1-r3 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 gentoo-dev

2022-08-09 07:08:25 UTC

Created attachment 798959 [details]
build.log

build log and emerge --info

Comment 2 Larry the Git Cow gentoo-dev

2022-10-13 09:06:58 UTC

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

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=bd7aa280e36e37620e378c70aed1f0c04c80969e

commit bd7aa280e36e37620e378c70aed1f0c04c80969e
Author:     Ionen Wolkens <ionen@gentoo.org>
AuthorDate: 2022-10-13 08:11:05 +0000
Commit:     Ionen Wolkens <ionen@gentoo.org>
CommitDate: 2022-10-13 09:06:07 +0000

    x11-libs/neXtaw: EAPI7->8, fix w/ clang16, -std=gnu89 + -fno-strict
    
    clang16 fixes regenerates some flex/yacc files so BDEPEND on them.
    
    Haven't looked for a proper fix wrt #864535, may be easy but
    passing -fno-strict-aliasing as better-than-nothing.
    
    Closes: https://bugs.gentoo.org/864535
    Closes: https://bugs.gentoo.org/871489
    Signed-off-by: Ionen Wolkens <ionen@gentoo.org>

 x11-libs/neXtaw/files/neXtaw-0.15.1-clang16.patch  | 27 ++++++++++++++++
 ...aw-0.15.1-r3.ebuild => neXtaw-0.15.1-r4.ebuild} | 37 +++++++++++++++-------
 2 files changed, 52 insertions(+), 12 deletions(-)