From: Jeff Law <jeffreyalaw@gmail.com>
To: Martin Sebor <msebor@gmail.com>, Paul Eggert <eggert@cs.ucla.edu>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH] avoid -Wuse-after-free [BZ #26779]
Date: Mon, 24 Jan 2022 18:08:00 -0700 [thread overview]
Message-ID: <9bd62338-fc2a-c9e8-f14b-df8c9a0f5f72@gmail.com> (raw)
In-Reply-To: <62758b96-42b1-c199-0bf1-975ca4b70cb0@gmail.com>
On 1/24/2022 5:42 PM, Martin Sebor via Libc-alpha wrote:
> On 1/21/22 17:42, Paul Eggert wrote:
>> On 1/21/22 15:14, Martin Sebor wrote:
>>>>
>>>
>>> That does look cleaner although it wasn't entirely obvious to me
>>> from looking at the code that it's the same. Unfortunately, it
>>> doesn't help. GCC replaces the bool variable with the equality
>>> test of the two pointers, and the warning points that out.
>>
>> That's a GCC bug.
>>
>>> Pedantically speaking it's a bug in GCC that it does that but
>>> I doubt anyone would care to do anything about it.
>>
>> You might be surprised; they do fix bugs in this area. If I could
>> reproduce the bug I'd file a bug report, but my GCC doesn't complain
>> so I guess it's up to you....
>
> I opened a GCC bug for the record:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104215
> GCC 12 is now in its regression-fixing stage so to get it fixed we'd
> need to make it a regression. That's usually only done for bugs that
> trigger under conditions where they didn't before.
The problem is there's no way for the compiler to know that it can't
move the use of q past the realloc call -- there's nothing from a
dataflow standpoint which would prevent such movement.
In some ways the builtin_realloc call would need to say "I'm going to
clobber this argument" and it would have to do so before translating
into SSA form I think.
Jeff
next prev parent reply other threads:[~2022-01-25 1:08 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-16 0:21 Martin Sebor
2022-01-16 2:25 ` Paul Eggert
2022-01-21 23:14 ` Martin Sebor
2022-01-22 0:42 ` Paul Eggert
2022-01-25 0:42 ` Martin Sebor
2022-01-25 1:08 ` Jeff Law [this message]
2022-01-18 9:48 ` Florian Weimer
2022-01-20 21:50 ` Martin Sebor
2022-01-25 0:52 ` [PATCH v2 0/5] " Martin Sebor
2022-01-25 0:57 ` [PATCH v2 1/5] " Martin Sebor
2022-01-25 17:46 ` Carlos O'Donell
2022-01-25 0:58 ` [PATCH v2 2/5] " Martin Sebor
2022-01-25 17:46 ` Carlos O'Donell
2022-01-25 0:58 ` [PATCH v2 3/5] " Martin Sebor
2022-01-25 17:47 ` Carlos O'Donell
2022-01-25 0:58 ` [PATCH v2 4/5] " Martin Sebor
2022-01-25 17:49 ` Carlos O'Donell
2022-01-25 17:51 ` Carlos O'Donell
2022-01-25 21:47 ` Florian Weimer
2022-01-26 13:55 ` Carlos O'Donell
2022-01-25 0:58 ` [PATCH v2 5/5] " Martin Sebor
2022-01-25 17:49 ` Carlos O'Donell
2022-01-25 22:50 ` [PATCH v3 " Martin Sebor
2022-01-26 14:56 ` Carlos O'Donell
2022-01-28 13:10 ` Joseph Myers
2022-01-28 17:33 ` Carlos O'Donell
2022-01-28 17:51 ` Joseph Myers
2022-01-28 23:21 ` Jeff Law
2022-01-31 15:12 ` Carlos O'Donell
2022-02-04 20:40 ` Joseph Myers
2022-01-25 17:46 ` [PATCH v2 0/5] " Carlos O'Donell
2022-01-26 3:08 ` Martin Sebor
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