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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 packagesAssignee: No maintainer - Look at if you want to take care of it <maintainer-needed>
Severity: normal    
Priority: Normal    
Version: unspecified   
Hardware: All   
OS: Linux   
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

Issue: x11-libs/neXtaw-0.15.1-r3 fails to compile (lto).
Discovered on: amd64 (internal ref: lto_tinderbox)

This machine uses lto with CFLAGS=-flto -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing

Here is a bit of explanation:

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.

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

Used to find possible runtime issues in packages. These bugs are a problem anyway but may be even worse when combined with LTO.

- 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:
Comment 1 Agostino Sarubbo gentoo-dev 2022-08-09 07:08:25 UTC
Created attachment 798959 [details]

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):

commit bd7aa280e36e37620e378c70aed1f0c04c80969e
Author:     Ionen Wolkens <>
AuthorDate: 2022-10-13 08:11:05 +0000
Commit:     Ionen Wolkens <>
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.
    Signed-off-by: Ionen Wolkens <>

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