Hi Jonathon,
On Wed, Oct 30, 2019 at 09:29:02PM -0500, Jonathon Anderson wrote:
> fake_{loc,loclists,addr}_cu are Dwarf_CUs that are created separate from
> all the others, so their contents are minimal and mostly initialized by
> a calloc. On dwarf_end however, they are freed through the same code path
> as all the others, so they call DAH_free like all the others. This changes
> that so that these three are exempt from DAH and split-DWARF matters, and
> swaps the calloc for a malloc so Memcheck will catch any others.
Thanks for catching that!
> ---
> Sorry to keep adding patches, but ran across this while tinkering about.
>
> Its not a current issue, but when the concurrent hash table is
> integrated this could cause some issues (on some system somewhere,
> maybe). In that case there are enough moving internals that a calloc
> may not initialize it properly.
>
> Its also an error waiting to happen, so this is this just cleans it
> up with some semblance of logical correctness.
Yes, this is very good. But... see below.
> (In other news, I finally figured out why git send-email wasn't
> working for me! Thanks for everyone's patience, especially
> Wielaard's :) )
Works perfectly.
> diff --git a/libdw/dwarf_begin_elf.c b/libdw/dwarf_begin_elf.c
> index 8d137414..1b2c5a45 100644
> --- a/libdw/dwarf_begin_elf.c
> +++ b/libdw/dwarf_begin_elf.c
> @@ -223,7 +223,7 @@ valid_p (Dwarf *result)
> inside the .debug_loc or .debug_loclists section. */
> if (result != NULL && result->sectiondata[IDX_debug_loc] != NULL)
> {
> - result->fake_loc_cu = (Dwarf_CU *) calloc (1, sizeof (Dwarf_CU));
> + result->fake_loc_cu = (Dwarf_CU *) malloc (sizeof (Dwarf_CU));
> if (unlikely (result->fake_loc_cu == NULL))
> {
> Dwarf_Sig8_Hash_free (&result->sig8_hash);
> @@ -240,12 +240,15 @@ valid_p (Dwarf *result)
> result->fake_loc_cu->endp
> = (result->sectiondata[IDX_debug_loc]->d_buf
> + result->sectiondata[IDX_debug_loc]->d_size);
> + result->fake_loc_cu->locs = NULL;
> + result->fake_loc_cu->address_size = 0;
> + result->fake_loc_cu->version = 0;
> }
> }
>
> if (result != NULL && result->sectiondata[IDX_debug_loclists] != NULL)
> {
> - result->fake_loclists_cu = (Dwarf_CU *) calloc (1, sizeof (Dwarf_CU));
> + result->fake_loclists_cu = (Dwarf_CU *) malloc (sizeof (Dwarf_CU));
> if (unlikely (result->fake_loclists_cu == NULL))
> {
> Dwarf_Sig8_Hash_free (&result->sig8_hash);
> @@ -263,6 +266,9 @@ valid_p (Dwarf *result)
> result->fake_loclists_cu->endp
> = (result->sectiondata[IDX_debug_loclists]->d_buf
> + result->sectiondata[IDX_debug_loclists]->d_size);
> + result->fake_loclists_cu->locs = NULL;
> + result->fake_loclists_cu->address_size = 0;
> + result->fake_loclists_cu->version = 0;
> }
> }
>
> @@ -272,7 +278,7 @@ valid_p (Dwarf *result)
> inside the .debug_addr section, if it exists. */
> if (result != NULL && result->sectiondata[IDX_debug_addr] != NULL)
> {
> - result->fake_addr_cu = (Dwarf_CU *) calloc (1, sizeof (Dwarf_CU));
> + result->fake_addr_cu = (Dwarf_CU *) malloc (sizeof (Dwarf_CU));
> if (unlikely (result->fake_addr_cu == NULL))
> {
> Dwarf_Sig8_Hash_free (&result->sig8_hash);
> @@ -291,6 +297,9 @@ valid_p (Dwarf *result)
> result->fake_addr_cu->endp
> = (result->sectiondata[IDX_debug_addr]->d_buf
> + result->sectiondata[IDX_debug_addr]->d_size);
> + result->fake_addr_cu->locs = NULL;
> + result->fake_addr_cu->address_size = 0;
> + result->fake_addr_cu->version = 0;
> }
> }
This all looks correct.
> diff --git a/libdw/dwarf_end.c b/libdw/dwarf_end.c
> index a2e94436..a32a149e 100644
> --- a/libdw/dwarf_end.c
> +++ b/libdw/dwarf_end.c
> @@ -52,18 +52,22 @@ cu_free (void *arg)
> {
> struct Dwarf_CU *p = (struct Dwarf_CU *) arg;
>
> - Dwarf_Abbrev_Hash_free (&p->abbrev_hash);
> -
> tdestroy (p->locs, noop_free);
>
> - /* Free split dwarf one way (from skeleton to split). */
> - if (p->unit_type == DW_UT_skeleton
> - && p->split != NULL && p->split != (void *)-1)
> + if(p != p->dbg->fake_loc_cu && p != p->dbg->fake_loclists_cu
> + && p != p->dbg->fake_addr_cu)
> {
> - /* The fake_addr_cu might be shared, only release one. */
> - if (p->dbg->fake_addr_cu == p->split->dbg->fake_addr_cu)
> - p->split->dbg->fake_addr_cu = NULL;
> - INTUSE(dwarf_end) (p->split->dbg);
> + Dwarf_Abbrev_Hash_free (&p->abbrev_hash);
> +
> + /* Free split dwarf one way (from skeleton to split). */
> + if (p->unit_type == DW_UT_skeleton
> + && p->split != NULL && p->split != (void *)-1)
> + {
> + /* The fake_addr_cu might be shared, only release one. */
> + if (p->dbg->fake_addr_cu == p->split->dbg->fake_addr_cu)
> + p->split->dbg->fake_addr_cu = NULL;
> + INTUSE(dwarf_end) (p->split->dbg);
> + }
> }
The Dwarf_Abbrev_Hash_free looks in the correct place. But I don't
believe the Free split dwarf hunk should not be under the same if
not-fake block.
Thanks,
Mark
