re_node_set_alloc relies on malloc(0) returning non-NULL

[Aharon Robbins]

Hi.

This code in regex_internal.c:

-------------------------------------
static reg_errcode_t
__attribute_warn_unused_result__
re_node_set_alloc (re_node_set *set, Idx size)
{
  set->alloc = size;
  set->nelem = 0;
  set->elems = re_malloc (Idx, size);
  if (__glibc_unlikely (set->elems == NULL))
    return REG_ESPACE;
  return REG_NOERROR;
}
-------------------------------------

If size is zero, malloc() is called with zero.  IIRC, it's formally
undefined what happens if malloc(0) is called, and NULL is a possibly
valid result.  If used with a malloc() that does return NULL, compilation
of a regex fails.  regex needs to take this into account.

This happened in gawk using the Persistent Memory Allocator (PMA).

I have worked around it with additional gawk-specific code that sets
size to 1 if it's 0.

Thanks,

Arnold