Re: [PATCH] PR/101135 - Load of null pointer when passing absent assumed-shape array argument for an optional dummy argument

[Harald Anlauf <anlauf@gmx.de>]

Hi Mikael,

Am 04.02.22 um 11:45 schrieb Mikael Morin:
> Hello,
>
> Le 29/01/2022 à 22:41, Harald Anlauf via Fortran a écrit :
>> The least invasive change - already pointed out by the reporter - is
>> to check the presence of the argument before dereferencing the data
>> pointer after the offset calculation.  This requires adjusting the
>> checking pattern for gfortran.dg/missing_optional_dummy_6a.f90.
>>
>> Regtesting reminded me that procedures with bind(c) attribute are doing
>> their own stuff, which is why they need to be excluded here, otherwise
>> testcase bind-c-contiguous-4.f90 would regress on the expected output.

only after submitting the patch I figured that the patch is incomplete.

When we have a call chain of procedures with and without bind(c),
there are still cases left where the failure with the sanitizer
is not fixed.  Just add "bind(c)" to subroutine test_wrapper only
in the original PR.

I have added a corresponding comment in the PR.

>> There is a potential alternative solution which I did not pursue, as I
>> think it is more invasive, but also that I didn't succeed to implement:
>> A non-present dummy array argument should not need to get its descriptor
>> set up.  Pursuing this is probably not the right thing to do during the
>> current stage of development and could be implemented later.  If somebody
>> believes this is important, feel free to open a PR for this.
>>
> I have an other (equally unimportant) concern that it may create an
> unnecessary conditional when passing a subobject of an optional
> argument.  In that case we can assume that the optional is present.
> It’s not a correctness issue, so let’s not bother at this stage.

Judging from the dump tree of the cases I looked at I did not see
anything that would pose a problem to the optimizer.

>> Regtested on x86_64-pc-linux-gnu.  OK for mainline?
>>
> OK.

Given my latest observations I'd rather withdraw the current version of
the patch and rethink.  I also did not see an issue with bind(c)
procedures calling alikes.

It would help if one would not only know the properties of the actual
argument, but also of the formal one, which is not available at that
point in the code.  I'll have another look and resubmit.

> Thanks.
>

Thanks for the review!

Harald