re PR sanitizer/63927 (AddressSanitizer painfully slow on ppc64)

2015-07-28  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	PR sanitizer/63927
	* sanitizer_common/sanitizer_stacktrace.cc
	(BufferedStackTrace::FastUnwindStack): Fix code for PowerPC to
	find the link register at an offset of 16 from the base of the
	caller's stack frame.

From-SVN: r226335

libsanitizer/ChangeLog

+2015-07-28  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
+
+	PR sanitizer/63927
+	* sanitizer_common/sanitizer_stacktrace.cc
+	(BufferedStackTrace::FastUnwindStack): Fix code for PowerPC to
+	find the link register at an offset of 16 from the base of the
+	caller's stack frame.
+
 2015-05-13  Michael Haubenwallner  <michael.haubenwallner@ssi-schaefer.com>
 
 	* Makefile.in: Regenerated with automake-1.11.6.

libsanitizer/sanitizer_common/sanitizer_stacktrace.cc

@@ -86,7 +86,18 @@ void BufferedStackTrace::FastUnwindStack(uptr pc, uptr bp, uptr stack_top,
   while (IsValidFrame((uptr)frame, stack_top, bottom) &&
          IsAligned((uptr)frame, sizeof(*frame)) &&
          size < max_depth) {
+#ifdef __powerpc__
+    // PowerPC ABIs specify that the return address is saved at offset
+    // 16 of the *caller's* stack frame.  Thus we must dereference the
+    // back chain to find the caller frame before extracting it.
+    uhwptr *caller_frame = (uhwptr*)frame[0];
+    if (!IsValidFrame((uptr)caller_frame, stack_top, bottom) ||
+	!IsAligned((uptr)caller_frame, sizeof(uhwptr)))
+      break;
+    uhwptr pc1 = caller_frame[2];
+#else
     uhwptr pc1 = frame[1];
+#endif
     if (pc1 != pc) {
       trace_buffer[size++] = (uptr) pc1;
     }