[MSan] [PowerPC] Dereference function descriptors when recording stack origins.

[aizatsky]

lib/msan/msan.cc

545

pc is sometimes 0 (see function above).

[• koriakin]

Whoops, of course it is. Fixed.

lib/msan/msan.cc

static const u32 first_timer =
       dash + (dash << 8) + (dash << 16) + (dash << 24);
   u32 *id_ptr = (u32*)descr;
   bool print = false;  // internal_strstr(descr + 4, "AllocaTOTest") != 0;
   u32 id = *id_ptr;
   if (id == first_timer) {
     u32 idx = atomic_fetch_add(&NumStackOriginDescrs, 1, memory_order_relaxed);
     CHECK_LT(idx, kNumStackOriginDescrs);
     StackOriginDescr[idx] = descr + 4;
+#if SANITIZER_PPC64V1
+    // On PowerPC64 ELFv1, the address of a function actually points to a
+    // three-doubleword data structure with the first field containing
+    // the address of the function's code.
+    if (pc)
+      pc = *reinterpret_cast<uptr*>(pc);
+#endif
     StackOriginPC[idx] = pc;
     id = Origin::CreateStackOrigin(idx).raw_id();
     *id_ptr = id;
     if (print)
       Printf("First time: idx=%d id=%d %s %p \n", idx, id, descr + 4, pc);
   }
   if (print)
     Printf("__msan_set_alloca_origin: descr=%s id=%x\n", descr + 4, id);