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Bug 861143 - media-video/vlc- fails to compile (lto): json.c:134:45: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
Summary: media-video/vlc- fails to compile (lto): json.c:134:45: error: der...
Alias: None
Product: Gentoo Linux
Classification: Unclassified
Component: Current packages (show other bugs)
Hardware: All Linux
: Normal normal (vote)
Assignee: Gentoo Media-video project
Keywords: PullRequest
Depends on:
Blocks: lto
  Show dependency tree
Reported: 2022-07-26 06:34 UTC by Agostino Sarubbo
Modified: 2022-10-12 08:15 UTC (History)
0 users

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

build.log (build.log,477.62 KB, text/plain)
2022-07-26 06:34 UTC, Agostino Sarubbo

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Description Agostino Sarubbo gentoo-dev 2022-07-26 06:34:16 UTC

Issue: media-video/vlc- 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 2022-07-26 06:34:19 UTC
Created attachment 794429 [details]

build log and emerge --info
Comment 2 Agostino Sarubbo gentoo-dev 2022-07-26 06:34:21 UTC
Error(s) that match a know pattern in addition to what has been reported in the summary:

configure: WARNING: Package 'libsystemd', required by 'virtual:world', not found.
fatal: not a git repository (or any parent up to mount point /var/tmp)
misc/webservices/json.c:134:45: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing[]]
Comment 3 Agostino Sarubbo gentoo-dev 2022-07-26 09:03:01 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 4 Larry the Git Cow gentoo-dev 2022-08-18 07:06:26 UTC
The bug has been referenced in the following commit(s):

commit 3d84addb0089529e1b6ef37cb19db59eb63a02cf
Author:     Petr Vaněk <>
AuthorDate: 2022-07-29 11:54:22 +0000
Commit:     Joonas Niilola <>
CommitDate: 2022-08-18 07:06:18 +0000

    dev-libs/json-parser: new package, add 1.1.0_p20211208
    Original version 1.1.0 is from a year 2014, which is quite old. The
    snapshot is from latest commit 531a49062975 ("Add author of #154 to
    AUTHORS") in master branch, which contains (among others) two fixes
    related to strict aliasing. New release is anticipated [1], but it is
    not clear when it will happen, as the ticket is open for 2 years
    It was necessary to apply one patch proposed as PR [2] to upstream,
    which changes pkgconfig file installation path from datadir to libdir.
    This library is currently known to be bundled in multiple packages in
    ::gentoo, see the corresponding bugs bellow.
    Signed-off-by: Petr Vaněk <>
    Signed-off-by: Joonas Niilola <>

 dev-libs/json-parser/Manifest                      |  1 +
 .../files/json-parser-1.1.0-pkgconfig-libdir.patch | 22 ++++++
 .../json-parser/json-parser-1.1.0_p20211208.ebuild | 82 ++++++++++++++++++++++
 dev-libs/json-parser/metadata.xml                  | 15 ++++
 4 files changed, 120 insertions(+)
Comment 5 Agostino Sarubbo gentoo-dev 2022-10-12 08:15:47 UTC
lto_tinderbox has reproduced this issue with version - Updating summary.