Gentoo Websites Logo
Go to: Gentoo Home Documentation Forums Lists Bugs Planet Store Wiki Get Gentoo!
Bug 854360 - app-editors/emacs-18.59-r14 fails to compile (lto): alloc.c:1085:20: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
Summary: app-editors/emacs-18.59-r14 fails to compile (lto): alloc.c:1085:20: error: d...
Alias: None
Product: Gentoo Linux
Classification: Unclassified
Component: Current packages (show other bugs)
Hardware: All Linux
: Normal normal (vote)
Assignee: GNU Emacs project
Keywords: NeedPatch
Depends on:
Blocks: lto
  Show dependency tree
Reported: 2022-06-26 07:03 UTC by Agostino Sarubbo
Modified: 2022-07-26 09:00 UTC (History)
0 users

See Also:
Package list:
Runtime testing required: ---

build.log (build.log,80.90 KB, text/plain)
2022-06-26 07:03 UTC, Agostino Sarubbo

Note You need to log in before you can comment on or make changes to this bug.
Description Agostino Sarubbo gentoo-dev 2022-06-26 07:03:23 UTC

Issue: app-editors/emacs-18.59-r14 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 2022-06-26 07:03:25 UTC
Created attachment 787682 [details]

build log and emerge --info
Comment 2 Sam James archtester Gentoo Infrastructure gentoo-dev Security 2022-06-26 07:04:30 UTC
For older Emacs, let's just use -fno-strict-aliasing.
Comment 3 Ulrich Müller gentoo-dev 2022-06-26 10:22:38 UTC
I must admit that I'm getting tired of bugs of this type. It's a strange idea to compile emacs:18 with that combination of CFLAGS. Also this isn't a real issue, otherwise users would have reported it earlier.

Maybe time to retire slot 18 (as well as 23 to 26), or move it to the emacs overlay?
Comment 4 Larry the Git Cow gentoo-dev 2022-06-26 10:34:21 UTC
The bug has been referenced in the following commit(s):

commit f32b8cd1cdedb9e74ecbd8a07244eaf5250a9e04
Author:     Ulrich Müller <>
AuthorDate: 2022-06-26 10:33:19 +0000
Commit:     Ulrich Müller <>
CommitDate: 2022-06-26 10:34:15 +0000

    app-editors/emacs: Compile Emacs 18 with -fno-strict-aliasing
    Suggested-by: Sam James <>
    Signed-off-by: Ulrich Müller <>

 app-editors/emacs/emacs-18.59-r14.ebuild | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
Comment 5 Agostino Sarubbo gentoo-dev 2022-07-26 09:00:14 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: