[Bug fortran/78387] OpenMP segfault/stack size exceeded writing to internal file

[wilson at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78387

Jim Wilson <wilson at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |wilson at gcc dot gnu.org

--- Comment #7 from Jim Wilson <wilson at gcc dot gnu.org> ---
The testcase can trigger the bug fixed in
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81195
if the number of threads is high enough.  It also triggers an unrelated problem
which gives the stack size exceeded error.

Looking at this issue, I see that in libgfortran/io/unit.c, the newunit_alloc
function starts with
      newunits = xcalloc (16, 1);
      newunit_size = 16;
and then if we need more of them, it does
  newunit_size *= 2;
  newunits = xrealloc (newunits, newunit_size);

However, for stash_internal_unit, we have as global definitions
  #define NEWUNIT_STACK_SIZE 16
  static gfc_saved_unit newunit_stack[NEWUNIT_STACK_SIZE];
and inside the function we have
  if (newunit_tos >= NEWUNIT_STACK_SIZE)

When the testcase fails, newunit_size is 32.  So we have allocated more units
than we can stash.

It looks like the fix is to change stash_internal_unit to dynamically resize
newunit_stack, same as the newunit_alloc function already does for newunits. 
This appears related to bug 48587, which added the code to increase the size of
newunits array.