Hi Gilles, > > I also found an other potential issue with copy-in. > > If in Fortran, we > > call foo(buf(0,0)) > > then the C subroutine can only access buf(0,0), and other elements such > as buf(1025,1025) cannot be accessed. > > Such elements are valid in buf, but out of bounds in the copy (that > contains a single element). > > Strictly speaking, I cannot say whether this is a violation of the > standard or not, but I can see how this will > > break a lot of existing apps (once again, those apps might be incorrect > in the first place, but most of us got used to them working).
The above call will only be conforming if the dummy argument is declared assumed or explicit size. Otherwise, the compiler should reject it due to rank mismatch. For assumed rank, the call would be legitimate, but the rank of the dummy argument is then zero. Even if no copy-in is performed, accessing data beyond the address range of that scalar is not strictly allowed. Of more interest is the situation where the dummy argument in Fortran is declared, e.g., TYPE(*), ASYNCHRONOUS, INTENT(IN) :: BUF(..) The standard's semantics *forbids* performing copy-in/out in this case, IIRC. Otherwise ASYNCHRONOUS semantics would not work, and non-blocking MPI calls would fail due to buffers vanishing into thin air. Regards Reinhold > > To me, this is a second reason why copy-in is not desirable (at least as > a default option). > > > > Cheers, > > > Gilles > > On 4/9/2019 7:18 PM, Paul Richard Thomas wrote: > > The most part of this patch is concerned with implementing calls from > > C of of fortran bind c procedures with assumed shape or assumed rank > > dummies to completely fix PR89843. The conversion of the descriptors > > from CFI to gfc occur on entry to and reversed on exit from the > > procedure. > > > > This patch is safe for trunk, even at this late stage, because its > > effects are barricaded behind the tests for CFI descriptors. I believe > > that it appropriately rewards the bug reporters to have this feature > > work as well as possible at release. > > > > Between comments and the ChangeLogs, this patch is self explanatory. > > > > Bootstrapped and regtested on FC29/x86_64 - OK for trunk? > > > > Paul > > > > 2019-04-09 Paul Thomas <pa...@gcc.gnu.org> > > > > PR fortran/89843 > > * trans-decl.c (gfc_get_symbol_decl): Assumed shape and assumed > > rank dummies of bind C procs require deferred initialization. > > (convert_CFI_desc): New procedure to convert incoming CFI > > descriptors to gfc types and back again. > > (gfc_trans_deferred_vars): Call it. > > * trans-expr.c (gfc_conv_gfc_desc_to_cfi_desc): Null the CFI > > descriptor pointer. Free the descriptor in all cases. > > > > PR fortran/90022 > > * trans-decl.c (gfc_get_symbol_decl): Make sure that the se > > expression is a pointer type before converting it to the symbol > > backend_decl type. > > > > 2019-04-09 Paul Thomas <pa...@gcc.gnu.org> > > > > PR fortran/89843 > > * gfortran.dg/ISO_Fortran_binding_4.f90: Modify the value of x > > in ctg. Test the conversion of the descriptor types in the main > > program. > > * gfortran.dg/ISO_Fortran_binding_10.f90: New test. > > * gfortran.dg/ISO_Fortran_binding_10.c: Called by it. > > > > PR fortran/90022 > > * gfortran.dg/ISO_Fortran_binding_1.c: Correct the indexing for > > the computation of 'ans'. Also, change the expected results for > > CFI_is_contiguous to comply with standard. > > * gfortran.dg/ISO_Fortran_binding_1.f90: Correct the expected > > results for CFI_is_contiguous to comply with standard. > > * gfortran.dg/ISO_Fortran_binding_9.f90: New test. > > * gfortran.dg/ISO_Fortran_binding_9.c: Called by it. > > > > 2019-04-09 Paul Thomas <pa...@gcc.gnu.org> > > > > PR fortran/89843 > > * runtime/ISO_Fortran_binding.c (cfi_desc_to_gfc_desc): Only > > return immediately if the source pointer is null. Bring > > forward the extraction of the gfc type. Extract the kind so > > that the element size can be correctly computed for sections > > and components of derived type arrays. Remove the free of the > > CFI descriptor since this is now done in trans-expr.c. > > (gfc_desc_to_cfi_desc): Only allocate the CFI descriptor if it > > is not null. > > (CFI_section): Normalise the difference between the upper and > > lower bounds by the stride to correctly calculate the extents > > of the section. > > > > PR fortran/90022 > > * runtime/ISO_Fortran_binding.c (CFI_is_contiguous) : Return > > 1 for true and 0 otherwise to comply with the standard. Correct > > the contiguity check for rank 3 and greater by using the stride > > measure of the lower dimension rather than the element length.
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