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Bug 861143 - media-video/vlc-3.0.17.4-r2 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-3.0.17.4-r2 fails to compile (lto): json.c:134:45: error: der...
Status: CONFIRMED
Alias: None
Product: Gentoo Linux
Classification: Unclassified
Component: Current packages (show other bugs)
Hardware: All Linux
: Normal normal (vote)
Assignee: Gentoo Media-video project
URL:
Whiteboard:
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: ---


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

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Description Agostino Sarubbo gentoo-dev 2022-07-26 06:34:16 UTC
https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/

Issue: media-video/vlc-3.0.17.4 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 2022-07-26 06:34:19 UTC
Created attachment 794429 [details]
build.log

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[https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wstrict-aliasing]]
Comment 3 Agostino Sarubbo gentoo-dev 2022-07-26 09:03:01 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 4 Larry the Git Cow gentoo-dev 2022-08-18 07:06:26 UTC
The bug has been referenced in the following commit(s):

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=3d84addb0089529e1b6ef37cb19db59eb63a02cf

commit 3d84addb0089529e1b6ef37cb19db59eb63a02cf
Author:     Petr Vaněk <arkamar@atlas.cz>
AuthorDate: 2022-07-29 11:54:22 +0000
Commit:     Joonas Niilola <juippis@gentoo.org>
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
    already.
    
    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.
    
    [1] https://github.com/json-parser/json-parser/issues/82
    [2] https://github.com/json-parser/json-parser/pull/164
    
    Bug: https://bugs.gentoo.org/858524
    Bug: https://bugs.gentoo.org/861143
    Bug: https://bugs.gentoo.org/861371
    Signed-off-by: Petr Vaněk <arkamar@atlas.cz>
    Signed-off-by: Joonas Niilola <juippis@gentoo.org>

 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 3.0.17.4-r2 - Updating summary.