Libbacktrace backtrace_vector_finish

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

I'm trying to understand how the backtrace_vector_* APIs are meant to work
and used, but at least for alloc.c don't see how it can work properly:

Both backtrace_vector_grow and backtrace_vector_release use
      base = realloc (vec->base, alc);
or
  vec->base = realloc (vec->base, vec->size);
(note, in the latter case it is even a memory leak if realloc fails),
but that assumes that that vec->base has been returned by malloc/realloc
etc.  But,
void 
backtrace_vector_finish (struct backtrace_state *state ATTRIBUTE_UNUSED,
                         struct backtrace_vector *vec)
{
  vec->base = (char *) vec->base + vec->size;
  vec->size = 0;
}
will change vec->base so that it no longer is an address returned by
malloc/realloc, so next time you call backtrace_vector_grow, if it will
actually need to reallocate anything, it will crash in realloc or silently
misbehave.  If this works properly in mmap.c implementation, perhaps
backtrace_vector_finish in alloc.c should just backtrace_vector_release
and memset (*vec, 0, sizeof (*vec)); ?

	Jakub