Bug 880571 – sys-libs/glibc-2.36-r5 fails tests on amd64 (LTO-SYSTEM)

• Product: Gentoo Linux
• Status: RESOLVED OBSOLETE

[Description Agostino Sarubbo 2022-11-09 07:58:28 UTC]

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

Issue: sys-libs/glibc-2.36-r5 fails tests (LTO-SYSTEM).
Discovered on: amd64 (internal ref: lto_tinderbox)

NOTE:
(LTO-SYSTEM) in the summary means that bug was found on a machine that runs lto but this bug MAY or MAY NOT BE related to lto.

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 2022-11-09 07:58:40 UTC]

Created attachment 829947 [details]
build.log.xz

build log and emerge --info (compressed because it exceeds attachment limit, use 'xzless' to read it)

[Comment 2 Agostino Sarubbo 2022-11-09 07:58:44 UTC]

Error(s) that match a know pattern:


FAIL: math/test-float-j1
FAIL: math/test-float-y0
FAIL: math/test-float-y1
FAIL: math/test-float32-j1
FAIL: math/test-float32-y0
FAIL: math/test-float32-y1
FAIL: misc/tst-bz21269
FAIL: string/tst-wcsncmp-rtm
sed: can't read /var/tmp/portage/sys-libs/glibc-2.36-r5/work/build-x86-x86_64-pc-linux-gnu-nptl/csu/32/crtn.o.dt: No such file or directory
sh: line 1: echo: write error: Broken pipe

[Comment 3 Andreas K. Hüttel 2022-11-12 18:20:03 UTC]

(In reply to Agostino Sarubbo from comment #2)
> Error(s) that match a know pattern:
> 
> 
> FAIL: math/test-float-j1
> FAIL: math/test-float-y0
> FAIL: math/test-float-y1
> FAIL: math/test-float32-j1
> FAIL: math/test-float32-y0
> FAIL: math/test-float32-y1
> FAIL: misc/tst-bz21269
> FAIL: string/tst-wcsncmp-rtm
> sed: can't read
> /var/tmp/portage/sys-libs/glibc-2.36-r5/work/build-x86-x86_64-pc-linux-gnu-
> nptl/csu/32/crtn.o.dt: No such file or directory
> sh: line 1: echo: write error: Broken pipe

Given that glibc uses filter-flags and thus drops anything LTO-related, this feels fishy.

Can't do anything without more details though (corresponding .out files from math/ directory)