Bug 878895

Summary:	sci-libs/libdap-3.20.9 fails tests (lto): ddsT.cc:237:44: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
Product:	Gentoo Linux	Reporter:	Agostino Sarubbo <ago>
Component:	Current packages	Assignee:	Sci-geo Project <sci-geosciences>
Status:	RESOLVED FIXED
Severity:	normal	CC:	eschwartz93
Priority:	Normal
Version:	unspecified
Hardware:	All
OS:	Linux
See Also:	https://github.com/OPENDAP/libdap4/issues/244
Whiteboard:
Package list:		Runtime testing required:	---
Bug Depends on:
Bug Blocks:	618550
Attachments:	build.log

Description Agostino Sarubbo gentoo-dev

2022-10-31 16:31:14 UTC

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

Issue: sci-libs/libdap-3.20.9 fails tests (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

2022-10-31 16:31:17 UTC

Created attachment 826241 [details]
build.log

build log and emerge --info

Comment 2 Eli Schwartz 2024-03-07 06:37:37 UTC

It fails with -Werror=odr during src_compile now, because we have better elibtoolize support.

Comment 3 Larry the Git Cow gentoo-dev

2024-03-07 11:51:01 UTC

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

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=d43c4ffe6a35183dd1794de3a74ab32befef0521

commit d43c4ffe6a35183dd1794de3a74ab32befef0521
Author:     Eli Schwartz <eschwartz93@gmail.com>
AuthorDate: 2024-03-07 06:50:52 +0000
Commit:     Sam James <sam@gentoo.org>
CommitDate: 2024-03-07 11:46:25 +0000

    sci-libs/libdap: mark as LTO-unsafe, strict-aliasing unsafe
    
    Closes: https://bugs.gentoo.org/878895
    Signed-off-by: Eli Schwartz <eschwartz93@gmail.com>
    Signed-off-by: Sam James <sam@gentoo.org>

 sci-libs/libdap/libdap-3.20.9.ebuild | 6 ++++++
 1 file changed, 6 insertions(+)