Re: [Outreachy] Return value before or after free()?

From: Miriam R. <mirucam@gmail.com>
Date: Jan 7, 2020, 20:40 UTC
Message-ID: <CAN7CjDAZCxEmkvkqOw++VvBwF54cn_S1J+Uem61aNvjA7F3AiQ@mail.gmail.com>
In-Reply-To: <20200107015859.GJ6570@camp.crustytoothpaste.net>

El mar., 7 ene. 2020 a las 2:59, brian m. carlson (<sandals@crustytoothpaste.net>) escribió:

Show 21 quoted lines

>
> 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.
>

Sorry for my late reply, but I have been traveling all day.

Don't worry Brian, I am working on finishing bisect-helper conversion from shell to C. I am planning to send a patch related with this function as part of a patch series. My patch only changes the static header to be used in bisect related files. My mentor (Christian Couder) detected this and suggested me to ask the community.

> 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.
>

Don't worry again, next time if my question is related to a patch I am going to send I will actively write it and this way there will be no confusion. :)

> Again, sorry about that.
> --
> brian m. carlson: Houston, Texas, US
> OpenPGP: https://keybase.io/bk2204