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Bug 857741

Summary: dev-ruby/nio4r-2.7.0 fails to compile (lto): ev.h:691:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
Product: Gentoo Linux Reporter: Agostino Sarubbo <ago>
Component: Current packagesAssignee: Gentoo Ruby Team <ruby>
Status: RESOLVED FIXED    
Severity: normal CC: esigra
Priority: Normal    
Version: unspecified   
Hardware: All   
OS: Linux   
URL: https://github.com/socketry/nio4r/issues/289
Whiteboard: Bundled/forked libev is broken, not much we can do except filter/append flags
Package list:
Runtime testing required: ---
Bug Depends on: 855869    
Bug Blocks: 251464, 618550    
Attachments: build.log

Description Agostino Sarubbo gentoo-dev 2022-07-12 06:45:21 UTC
https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/

Issue: dev-ruby/nio4r-2.5.8 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
Comment 1 Agostino Sarubbo gentoo-dev 2022-07-12 06:45:24 UTC
Created attachment 791135 [details]
build.log

build log and emerge --info
Comment 2 Agostino Sarubbo gentoo-dev 2022-07-26 09:01:18 UTC
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 3 Agostino Sarubbo gentoo-dev 2024-02-28 08:34:04 UTC
lto_tinderbox has reproduced this issue with version 2.7.0 - Updating summary.
Comment 4 Larry the Git Cow gentoo-dev 2024-02-29 00:50:45 UTC
The bug has been closed via the following commit(s):

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=7c5bf9a42324f8c9958f7f251d0396868b3e9481

commit 7c5bf9a42324f8c9958f7f251d0396868b3e9481
Author:     Sam James <sam@gentoo.org>
AuthorDate: 2024-02-29 00:50:05 +0000
Commit:     Sam James <sam@gentoo.org>
CommitDate: 2024-02-29 00:50:07 +0000

    dev-ruby/nio4r: filter LTO, no-SA
    
    Broken quite badly via bundled liebv, no upstream bug tracker for libev AFAICT. And
    broken in many bundled copies all over the place (which are modified...)
    
    Closes: https://bugs.gentoo.org/857741
    Signed-off-by: Sam James <sam@gentoo.org>

 dev-ruby/nio4r/nio4r-2.5.9.ebuild | 8 ++++++--
 dev-ruby/nio4r/nio4r-2.6.1.ebuild | 8 ++++++--
 dev-ruby/nio4r/nio4r-2.7.0.ebuild | 8 ++++++--
 3 files changed, 18 insertions(+), 6 deletions(-)