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

El mar., 7 ene. 2020 a las 2:59, brian m. carlson
([off-list ref]) escribió:

On 2020-01-07 at 01:08:09, brian m. carlson wrote:

quoted

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