Re: [Patch, Fortran] libgfortran's ISO_Fortran_binding.c: Use GCC11 version for backward-only code [PR108056]

[Harald Anlauf <anlauf@gmx.de>]

Hi Tobias,

Am 13.12.22 um 17:29 schrieb Tobias Burnus:
> This is a 12/13 regression as come changes to fix the GFC/CFI descriptor
> that went into GCC 12 fail with the (bogus) descriptor passed via by a
> GCC-11-compiled program.
>
> As later GCC 12 changes moved the descriptor to the front end, those
> functions are only in libgomp.so to cater for old program. Richard
> suggested in the PR that the best way is to move to the GCC 11 version,
> such that libgfortran.so won't regress.

that appears to be the most reasonable & practical way to go.

> I now did so - except for three fixes (cf. changelog). See also
> PR: https://gcc.gnu.org/PR108056
>
> There is no testcase as it needs to be compiled by GCC <= 11 and then
> run with linking (dynamically) to a GCC 12 or 13 libgfortran.

I've verified that the testcase in the PR does not crash with
the re-modified libgfortran.

I've looked at the resulting ISO_Fortran_binding.c vs. the 11-branch
version and am still trying to understand the resulting differences
in the code, in what respect they might be relevant or not.

Given that this is a somewhat delicate situation we're in, is there
a set of tests that I could run *manually* (i.e. compile with gcc-11
and link with gcc-12/13) to verify that this best-effort fix should
be good enough for the common user?

Just a suggestion of a few "randomly" chosen tests?

> OK for mainline and GCC 12?
>
>   * * *
>
> Note: It is strongly recommended to use GCC 12 (or 13) with
> array-descriptor
> C interop as many issues were fixed. Like for the testcase in the PR; in
> GCC 11
> the type arriving in libgomp is BT_ASSUME ('type(*)'). But as the effective
> argument is passed as array descriptor through out, the 'float'
> (real(4)) type
> info is actually preservable (as GCC 12 cf. testcase of comment 0 and my
> comment
> in the PR for the C part of the testcase).(*)

Well, in the real world there are larger installations with large
software stacks, and it is easier said to "compile each component
with the same compiler version" than done...

(I've just had another personal experience during my daytime job.)

Thanks for your effort so far!

Harald

> Tobias
>
> ((*) This is not possible if using a scalar 'type(*)' or a
> non-array-descriptor
> array in between. I think GCC 12 uses 'CFI_other' in the
> information-is-lost case.)
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