From: Alex Colomar <alx.manpages@gmail.com>
To: Martin Uecker <uecker@tugraz.at>, GCC <gcc@gcc.gnu.org>,
Jonathan Wakely <jwakely.gcc@gmail.com>
Cc: "Iker Pedrosa" <ipedrosa@redhat.com>,
"Florian Weimer" <fweimer@redhat.com>,
"Paul Eggert" <eggert@cs.ucla.edu>,
"Michael Kerrisk" <mtk.manpages@gmail.com>,
"Jₑₙₛ Gustedt" <jens.gustedt@inria.fr>,
"David Malcolm" <dmalcolm@redhat.com>,
"Sam James" <sam@gentoo.org>, "Serge Hallyn" <serge@hallyn.com>
Subject: Re: Missed warning (-Wuse-after-free)
Date: Thu, 23 Feb 2023 20:23:20 +0100 [thread overview]
Message-ID: <b18a74df-d18e-dc82-b001-5ec65e7c6b26@gmail.com> (raw)
In-Reply-To: <6edeb3c197c327c1c6639d322c53ec6056039a33.camel@tugraz.at>
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Hi Martin,
On 2/17/23 14:48, Martin Uecker wrote:
>> This new wording doesn't even allow one to use memcmp(3);
>> just reading the pointer value, however you do it, is UB.
>
> memcmp would not use the pointer value but work
> on the representation bytes and is still allowed.
Hmm, interesting. It's rather unspecified behavior. Still
unpredictable: (memcmp(&p, &p, sizeof(p) == 0) might evaluate to true or
false randomly; the compiler may compile out the call to memcmp(3),
since it knows it won't produce any observable behavior.
<https://software.codidact.com/posts/287905>
Cheers!
Alex
--
<http://www.alejandro-colomar.es/>
GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5
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next prev parent reply other threads:[~2023-02-23 19:23 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-16 14:35 Alejandro Colomar
2023-02-16 15:15 ` David Malcolm
2023-02-17 1:04 ` Alejandro Colomar
2023-02-17 1:05 ` Alejandro Colomar
2023-02-17 1:56 ` Sam James
2023-02-17 8:12 ` Martin Uecker
2023-02-17 11:35 ` Alejandro Colomar
2023-02-17 13:34 ` Andreas Schwab
2023-02-17 13:48 ` Martin Uecker
2023-02-23 19:23 ` Alex Colomar [this message]
2023-02-23 19:57 ` Martin Uecker
2023-02-24 0:02 ` Alex Colomar
2023-02-24 1:21 ` Serge E. Hallyn
2023-02-24 1:42 ` Alex Colomar
2023-02-24 3:01 ` Peter Lafreniere
2023-02-24 8:52 ` Martin Uecker
2023-02-24 8:43 ` Martin Uecker
2023-02-24 16:10 ` Serge E. Hallyn
2023-02-24 8:36 ` Martin Uecker
2023-02-24 16:01 ` Serge E. Hallyn
2023-02-24 16:37 ` Martin Uecker
2023-02-17 3:48 ` Siddhesh Poyarekar
2023-02-17 11:22 ` Alejandro Colomar
2023-02-17 13:38 ` Siddhesh Poyarekar
2023-02-17 14:01 ` Mark Wielaard
2023-02-17 14:06 ` Siddhesh Poyarekar
2023-02-17 21:20 ` [PATCH] Make -Wuse-after-free=3 the default one in -Wall Alejandro Colomar
2023-02-17 21:39 ` Siddhesh Poyarekar
2023-02-17 21:41 ` Siddhesh Poyarekar
2023-02-17 22:58 ` Alejandro Colomar
2023-02-17 23:03 ` Siddhesh Poyarekar
2023-02-17 11:24 ` Missed warning (-Wuse-after-free) Jonathan Wakely
2023-02-17 11:43 ` Alejandro Colomar
2023-02-17 12:04 ` Jonathan Wakely
2023-02-17 12:53 ` Siddhesh Poyarekar
2023-02-17 14:10 ` Jonathan Wakely
2023-02-17 13:44 ` David Malcolm
2023-02-17 14:01 ` Siddhesh Poyarekar
2023-02-17 8:49 ` Yann Droneaud
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