Re: [RFA] Fix leak in linespec.c

Simon Marchi
2019-01-08T23:39:50Z

On 2019-01-08 1:24 a.m., Philippe Waroquiers wrote:
> Valgrind reports a leak in many tests, such as:
> ==9382== 16 bytes in 1 blocks are definitely lost in loss record 236 of 3,282
> ==9382== at 0x4C2BE6D: malloc (vg_replace_malloc.c:309)
> ==9382== by 0x4197AF: xrealloc (common-utils.c:64)
> ==9382== by 0x51D16A: xresizevec<linespec_canonical_name> (poison.h:170)
> ==9382== by 0x51D16A: add_sal_to_sals(linespec_state*, std::vector<symtab_and_line, std::allocator<symtab_and_line> >*, symtab_and_line*, char const*, int) (linespec.c:1041)
> ==9382== by 0x51E2BF: create_sals_line_offset (linespec.c:2215)
> ==9382== by 0x51E2BF: convert_linespec_to_sals(linespec_state*, linespec*) (linespec.c:2358)
> ==9382== by 0x521B5D: convert_explicit_location_to_sals (linespec.c:2473)
>
> Fix leak by xfree-ing self->canonical_names in linespec_state_destructor.
> The leak probably appeared with the patch 'Remove cleanup from linespec.c',
> as there was a cleanup to xfree canonical_names before the patch.
>
> Tested on Debian/amd64, native and under valgrind.
>
> 2019-01-07 Philippe Waroquiers <philippe.waroquiers@skynet.be>
>
> * linespec.c (linespec_state_destructor): Free self->canonical_names.
> ---
> gdb/linespec.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/gdb/linespec.c b/gdb/linespec.c
> index b1ab462e66..f6ef4c2c40 100644
> --- a/gdb/linespec.c
> +++ b/gdb/linespec.c
> @@ -2767,6 +2767,7 @@ static void
> linespec_state_destructor (struct linespec_state *self)
> {
> htab_delete (self->addr_set);
> + xfree (self->canonical_names);
> }
>
> /* Delete a linespec parser. */
>

Ah, indeed. The original code in decode_line_full looks like:

/* Arrange for allocated canonical names to be freed. */
if (!result.empty ())
{
int i;

make_cleanup (xfree, state->canonical_names);
for (i = 0; i < result.size (); ++i)
{
gdb_assert (state->canonical_names[i].suffix != NULL);
make_cleanup (xfree, state->canonical_names[i].suffix);
}
}

... so you are adding the equivalent of the first cleanup.

It would be nice to be able to free the suffix strings in linespec_state_destructor, the
only problem is that we don't know the size of the canonical_names array at that point.

Anyway, LGTM, thanks!

Simon