From: "Rémi Denis-Courmont" <remi@remlab.net>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 1/5] lavu/common.h: Fix UB in av_clipl_int32_c()
Date: Thu, 30 May 2024 22:20:59 +0300
Message-ID: <6026291.GktK4fWIea@basile.remlab.net> (raw)
In-Reply-To: <20240530190713.GB2821752@pb2>
Le torstaina 30. toukokuuta 2024, 22.07.13 EEST Michael Niedermayer a écrit :
> If the function doesnt get called with values triggering UB then its not UB.
As Tomas pointed out, that statement is actually false. Specifically, if the
compiler can prove that the function can be called with values triggering UB,
then the code is UB, even if those offending values do not actually occur in a
given instance of the program.
The C specification is known to contradict causality.
For instance, if you have pass an uninitialised value to av_clipl_int32_c(),
then the code is UB, even if the actual value in the register or stack slot is
never one that could trigger UB. Of course, usage of uninitialised values is a
bad practice, but it is not, per se, UB.
--
レミ・デニ-クールモン
http://www.remlab.net/
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next prev parent reply other threads:[~2024-05-30 19:21 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-29 22:13 Tomas Härdin
2024-05-29 22:13 ` [FFmpeg-devel] [PATCH 2/5] lavu/common.h: Fix UB in av_clip_intp2_c() Tomas Härdin
2024-05-29 22:24 ` Andreas Rheinhardt
2024-05-29 23:08 ` Tomas Härdin
2024-05-29 22:14 ` [FFmpeg-devel] [PATCH 3/5] lavu/common.h: Fix UB in av_clip_uintp2_c() Tomas Härdin
2024-05-31 0:27 ` Michael Niedermayer
2024-05-29 22:14 ` [FFmpeg-devel] [PATCH 4/5] lavu/intmath.h: Fix UB in ff_ctz_c() and ff_ctzll_c() Tomas Härdin
2024-05-30 7:54 ` Rémi Denis-Courmont
2024-05-30 9:50 ` Tomas Härdin
2024-05-30 12:29 ` Hendrik Leppkes
2024-05-30 13:06 ` Rémi Denis-Courmont
2024-05-30 14:03 ` Tomas Härdin
2024-05-30 14:32 ` Rémi Denis-Courmont
2024-05-31 0:43 ` Ronald S. Bultje
2024-05-31 0:41 ` Michael Niedermayer
2024-05-31 5:48 ` Rémi Denis-Courmont
2024-05-31 0:31 ` Michael Niedermayer
2024-05-29 22:15 ` [FFmpeg-devel] [PATCH 5/5] lavu/mathematics: Return early if either a or b is zero Tomas Härdin
2024-05-31 0:22 ` Michael Niedermayer
2024-05-31 15:21 ` Tomas Härdin
2024-05-29 22:31 ` [FFmpeg-devel] [PATCH 1/5] lavu/common.h: Fix UB in av_clipl_int32_c() Andreas Rheinhardt
2024-05-30 9:48 ` Tomas Härdin
2024-05-30 6:41 ` Rémi Denis-Courmont
2024-05-30 9:40 ` Tomas Härdin
2024-05-30 11:50 ` Rémi Denis-Courmont
2024-05-30 14:07 ` Tomas Härdin
2024-05-30 14:28 ` Rémi Denis-Courmont
2024-05-30 15:32 ` Tomas Härdin
2024-05-30 15:38 ` Rémi Denis-Courmont
2024-05-31 1:03 ` Michael Niedermayer
2024-06-03 7:32 ` Rémi Denis-Courmont
2024-06-03 21:21 ` Michael Niedermayer
2024-05-30 15:42 ` James Almer
2024-05-30 16:48 ` Tomas Härdin
2024-05-30 17:49 ` Rémi Denis-Courmont
2024-05-30 19:07 ` Michael Niedermayer
2024-05-30 19:20 ` Rémi Denis-Courmont [this message]
2024-05-31 15:23 ` Tomas Härdin
2024-06-14 12:31 ` Tomas Härdin
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