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

[Mikael Morin <morin-mikael@orange.fr>]

Hello,

Le 29/01/2022 à 22:41, Harald Anlauf via Fortran a écrit :
> Dear Fortranners,
> 
> compiling with -fsanitize=undefined shows that we did mishandle the
> case where a missing optional argument is passed to another procedure.
> 
> Besides the example given in the PR, the existing testcase
> fortran.dg/missing_optional_dummy_6a.f90 fails with:
> 
> gcc/testsuite/gfortran.dg/missing_optional_dummy_6a.f90:21:29: runtime error: load of null pointer of type 'integer(kind=4)'
> gcc/testsuite/gfortran.dg/missing_optional_dummy_6a.f90:22:30: runtime error: load of null pointer of type 'integer(kind=4)'
> gcc/testsuite/gfortran.dg/missing_optional_dummy_6a.f90:27:29: runtime error: load of null pointer of type 'integer(kind=4)'
> 
> 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.
> 
> I've created a testcase that uses this PR's input as well as the lesson
> learned from studying the bind(c) testcase and placed this in the asan
> subdirectory.
> 
> 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.

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

Thanks.