[PATCH] Fix buffer overrun found by Coverity

[Gary Benson]

Tom Tromey wrote:
> >>>>> "Gary" == Gary Benson <gbenson@redhat.com> writes:
> 
> Gary> I would have committed this as obvious, but the testsuite
> Gary> doesn't exercise this piece of code; I can't realistically
> Gary> say I've regression tested this change, so I'd like another
> Gary> pair of eyes on it to be sure.
> 
> What about the fission-dwp.exp board maybe?
> Or one of the other boards.

Oh, good call, it does.

> Gary> -      memset (ids, 255, (DW_SECT_MAX + 1) * sizeof (int32_t));
> Gary> -      memset (ids_seen, 255, (DW_SECT_MAX + 1) * sizeof (int32_t));
> Gary> +      memset (ids, 255, sizeof_ids);
> Gary> +      memset (ids_seen, 255, sizeof (ids_seen));
> 
> Later the code does this:
> 
> 	  if (id < DW_SECT_MIN || id > DW_SECT_MAX)
> 	    {
> 	      error (_("Dwarf Error: bad DWP hash table, bad section id %d"
> [...]
> 	  ids_seen[id] = i;
> 	  ids[i] = id;
> 
> So I think it would be good to ensure that MAX_NR_V2_DWO_SECTIONS is
> >= DW_SECT_MAX + 1.  At least if I'm understanding this properly.

I don't *think* it's necessary:

 ids_seen is indexed by "id",
 which is 1 <= id <= DW_SECT_MAX;

 ids is indexed by "i",
 which is 0 <= i < nr_columns,
 and nr_columns is nr_columns <= MAX_NR_V2_DWO_SECTIONS,
 so 0 <= i < MAX_NR_V2_DWO_SECTIONS.

i.e. the dimensions are right, it's just the memset which isn't.
I think!

Ok, so this one's built and regtested on RHEL 7.5 x86_64 now, with
the fission-dwp.exp board.  Assuming the dimensions thing above is
correct, is this ok to commit?

Cheers,
Gary