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From: "joel at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/51073] New: _gfortran_caf_register incorrectly assumes malloc(0) returns non-NULL
Date: Thu, 10 Nov 2011 07:39:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51073

             Bug #: 51073
           Summary: _gfortran_caf_register incorrectly assumes malloc(0)
                    returns non-NULL
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: joel@gcc.gnu.org


Revision: Wed Nov  9 13:24:05 UTC 2011 (revision 181203)
Target: mips-rtems4.11 but impacts all where malloc(0) returns NULL

I am debugging why some of the gfortran tests are failing.  I have tracked NN
failures down to this code in caf/mpi.c around line 155.


  /* Token contains only a list of pointers.  */
  local = malloc (size);
  token = malloc (sizeof (void*) * caf_num_images);

  if (unlikely (local == NULL || token == NULL))
    goto error;

>>From http://pubs.opengroup.org/onlinepubs/009695399/functions/malloc.html

Upon successful completion with size not equal to 0, malloc() shall return a
pointer to the allocated space. If size is 0, either a null pointer or a unique
pointer that can be successfully passed to free() shall be returned. Otherwise,
it shall return a null pointer [CX]   and set errno to indicate the error. 

The code uses the memory pointed to by local to pass to MPI_Allgather() and
then returns it to the caller.  I suspect that the line "local = malloc (size)"
should be something like:

  local = malloc ((size == 0)? sizeof(XXX) : size);

Where XXX needs to be the type of one entity of sufficient size to pass into
MPI_Allgather.