Bug 910438

Summary:	app-arch/lbzip2: Sometimes produces corrupt archives when compiled with clang and vectorization with certain march values.
Product:	Gentoo Linux	Reporter:	Violet Purcell <vimproved>
Component:	Current packages	Assignee:	Matt Turner <mattst88>
Status:	RESOLVED FIXED
Severity:	normal	CC:	ionen, lockalsash, sam, toolchain, vimproved
Priority:	Normal	Keywords:	PullRequest
Version:	unspecified
Hardware:	All
OS:	Linux
See Also:	https://bugs.gentoo.org/show_bug.cgi?id=476682 https://github.com/llvm/llvm-project/issues/87189 https://github.com/gentoo/gentoo/pull/37515
Whiteboard:
Package list:		Runtime testing required:	---
Bug Depends on:
Bug Blocks:	408963, 915000

Description Violet Purcell 2023-07-16 20:13:39 UTC

This is a really odd and specific bug that only happens under specific circumstances (most likely caused by UB), but it is reproducable.

Reproducible: Always

Steps to Reproduce:
1. Compile app-arch/lbzip2 with clang and CFLAGS="-march=skylake -O1 -fvectorize"
2. Copy an environment.bz2 file from /var/db/pkg (specifically reproduced using /var/db/pkg/dev-python/setuptools-68.0.0-r1/environment.bz2)
3. bunzip2 environment.bz2 && lbzip2 -9 environment && bunzip2 environment.bz2
4. You should get a Data integrity error.



This bug only happens with clang, and can be reproduced using either of the following CFLAGS:
CFLAGS="-march=skylake -O1 -fvectorize"
CFLAGS="-mavx512f -O1 -fvectorize"

Comment 1 Sv. Lockal 2024-02-15 08:23:21 UTC

I had the same issue with `clang -flto=thin -O2 -march=native` system (znver4). Got a lot of broken environment.bz2 files. Maybe this is related to https://phabricator.wikimedia.org/T208647, but I just want to confirm that it is unsafe to use lbzip2 as bzip2 alternative in such conditions.

Comment 2 Sv. Lockal 2024-03-31 11:24:42 UTC

Reported to LLVM as https://github.com/llvm/llvm-project/issues/87189.

Workaround is:

  tc-is-clang && append-flags "-mno-avx512f"

Comment 3 Violet Purcell 2024-04-01 13:26:56 UTC

Thanks for the more detailed analysis.

Comment 4 Larry the Git Cow gentoo-dev

2025-01-10 00:31:54 UTC

The bug has been closed via the following commit(s):

https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=4ef726839f212339d1244880c029d6b89a59d71e

commit 4ef726839f212339d1244880c029d6b89a59d71e
Author:     Sv. Lockal <lockalsash@gmail.com>
AuthorDate: 2024-07-11 17:23:13 +0000
Commit:     Sam James <sam@gentoo.org>
CommitDate: 2025-01-10 00:29:32 +0000

    app-arch/lbzip2: fix archive corruption due to clang/avx512 miscompilation
    
    Closes: https://bugs.gentoo.org/910438
    Signed-off-by: Sv. Lockal <lockalsash@gmail.com>
    Closes: https://github.com/gentoo/gentoo/pull/37515
    Signed-off-by: Sam James <sam@gentoo.org>

 ...bzip2-2.5_p20181227-r2.ebuild => lbzip2-2.5_p20181227-r3.ebuild} | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)