Bug 861932 – net-wireless/libxtrxll-0.0_p20201202 fails to compile (lto): xtrxll_pcie_linux.c:127:19: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]

• Status: CONFIRMED
• Product: Gentoo Linux

[Description Agostino Sarubbo 2022-07-29 08:59:26 UTC]

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

Issue: net-wireless/libxtrxll-0.0_p20201202 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 2022-07-29 08:59:28 UTC]

Created attachment 795452 [details]
build.log

build log and emerge --info

[Comment 2 Agostino Sarubbo 2022-07-29 08:59:30 UTC]

Error(s) that match a know pattern in addition to what has been reported in the summary:


--   Package 'libusb3380', required by 'virtual:world', not found
FAILED: CMakeFiles/xtrxll.dir/xtrxll_base.c.o 
FAILED: mod_pcie/CMakeFiles/xtrxll_pcie.dir/xtrxll_pcie_linux.c.o 
/var/tmp/portage/net-wireless/libxtrxll-0.0_p20201202/work/libxtrxll-1b6eddfbedc700efb6f7e3c3594e43ac6ff29ea4/mod_pcie/xtrxll_pcie_linux.c:127:19: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]