On Mon, 22 Jul 2013, Ian Lance Taylor wrote:
> Thanks for noticing the problem. This patch isn't enough by itself.
> The code has to protect itself against the list changing in
> mid-stream. See dwarf_fileline in dwarf.c.
Thank you. Here's the updated patch, however I have to admit it's not
entirely clear to me what __sync_bool_compare_and_swap should achieve. Is it
only to ensure that we do not use a partially updated pointer (which shouldn't
happen with a naturally aligned pointer on hardware that updates cache lines
atomically)?
2013-07-22 Alexander Monakov <amona...@ispras.ru>
* elf.c (elf_syminfo): Loop over the elf_syminfo_data chain.
diff --git a/libbacktrace/elf.c b/libbacktrace/elf.c
index ef9bcdf..1d64a1f 100644
--- a/libbacktrace/elf.c
+++ b/libbacktrace/elf.c
@@ -454,12 +454,46 @@ elf_syminfo (struct backtrace_state *state, uintptr_t pc,
void *data)
{
struct elf_syminfo_data *edata;
- struct elf_symbol *sym;
+ struct elf_symbol *sym = NULL;
+
+ if (!state->threaded)
+ {
+ for (edata = (struct elf_syminfo_data *) state->syminfo_data;
+ edata;
+ edata = edata->next)
+ {
+ sym = ((struct elf_symbol *)
+ bsearch (&pc, edata->symbols, edata->count,
+ sizeof (struct elf_symbol), elf_symbol_search));
+ if (sym != NULL)
+ break;
+ }
+ }
+ else
+ {
+ struct elf_syminfo_data **pp;
+
+ pp = (struct elf_syminfo_data **) (void *) &state->syminfo_data;
+ while (1)
+ {
+ edata = *pp;
+ /* Atomic load. */
+ while (!__sync_bool_compare_and_swap (pp, edata, edata))
+ edata = *pp;
+
+ if (edata == NULL)
+ break;
+
+ sym = ((struct elf_symbol *)
+ bsearch (&pc, edata->symbols, edata->count,
+ sizeof (struct elf_symbol), elf_symbol_search));
+ if (sym != NULL)
+ break;
+
+ pp = &edata->next;
+ }
+ }
- edata = (struct elf_syminfo_data *) state->syminfo_data;
- sym = ((struct elf_symbol *)
- bsearch (&pc, edata->symbols, edata->count,
- sizeof (struct elf_symbol), elf_symbol_search));
if (sym == NULL)
callback (data, pc, NULL, 0);
else
