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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>
Severity: normal CC: esigra
Priority: Normal    
Version: unspecified   
Hardware: All   
OS: Linux   
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

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

build log and emerge --info
Comment 2 Agostino Sarubbo gentoo-dev 2022-07-26 09:01:18 UTC
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 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):

commit 7c5bf9a42324f8c9958f7f251d0396868b3e9481
Author:     Sam James <>
AuthorDate: 2024-02-29 00:50:05 +0000
Commit:     Sam James <>
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...)
    Signed-off-by: Sam James <>

 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(-)