From: "brian m. carlson" <sandals@crustytoothpaste.net>
To: Jeff King <peff@peff.net>, "Miriam R." <mirucam@gmail.com>,
git <git@vger.kernel.org>
Subject: Re: [Outreachy] Return value before or after free()?
Date: Tue, 7 Jan 2020 01:58:59 +0000 [thread overview]
Message-ID: <20200107015859.GJ6570@camp.crustytoothpaste.net> (raw)
In-Reply-To: <20200107010809.GH6570@camp.crustytoothpaste.net>
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On 2020-01-07 at 01:08:09, brian m. carlson wrote:
> Unfortunately, compilers have gotten much more aggressive about assuming
> that undefined behavior never occurs and rewriting code based on that.
> clang is not as bad about doing that, but GCC is very aggressive about
> it. There are multiple instances where NULL pointer checks have been
> optimized out because the compiler exploited undefined behavior to
> assume a pointer was never NULL.
>
> In this case, the only case in which we can safely assume that this
> behavior is acceptable is that r is NULL, in which case C11 tells us
> that "no action occurs" due to the free. So the compiler could just
> optimize this out to a "return 0". Just because it doesn't now doesn't
> mean we can assume it won't in the future, so we do need to fix this.
>
> I'll send a patch.
Oof, I just realized that you had tagged this with "[Outreachy]", which
means that you were probably planning on sending a patch to fix this,
and then I went and did it instead, so let me apologize for doing that.
I sent it because oftentimes we say "we should fix this thing" and then
never do it because nobody sends a patch, but in this case I should have
paid more attention and waited for you to respond and send one instead.
Again, sorry about that.
--
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204
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next prev parent reply other threads:[~2020-01-07 1:59 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-06 21:15 [Outreachy] Return value before or after free()? Miriam R.
2020-01-06 21:30 ` Jeff King
2020-01-06 22:47 ` Jonathan Nieder
2020-01-06 23:34 ` Andreas Schwab
2020-01-07 1:08 ` brian m. carlson
2020-01-07 1:58 ` brian m. carlson [this message]
2020-01-07 20:40 ` Miriam R.
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