Re: [PATCH, RFC] Enable libsanitizer on powerpc{,64}

[Peter Bergner <bergner at vnet dot ibm dot com>]

On Tue, 2012-11-20 at 23:24 +0400, Konstantin Serebryany wrote:
> On Tue, Nov 20, 2012 at 11:08 PM, Peter Bergner <bergner@vnet.ibm.com> wrote:
> > diff -urpN -X /home/bergner/cvs/dontdiff gcc-fsf-mainline-kcc/libsanitizer/sanitizer_common/sanitizer_stacktrace.h gcc-fsf-mainline-asan/libsanitizer/sanitizer_common/sanitizer_stacktrace.h
> > --- gcc-fsf-mainline-kcc/libsanitizer/sanitizer_common/sanitizer_stacktrace.h   2012-11-20 11:42:08.821389243 -0600
> > +++ gcc-fsf-mainline-asan/libsanitizer/sanitizer_common/sanitizer_stacktrace.h  2012-11-20 11:12:44.551390980 -0600
> > @@ -23,6 +23,7 @@ struct StackTrace {
> >    uptr size;
> >    uptr max_size;
> >    uptr trace[kStackTraceMax];
> > +  uptr frame[kStackTraceMax];  // For use by _Unwind_Backtrace architectures.
> 
> This is bad. The objects of this type are already too big, we should
> not make them 2x larger.
> Hopefully Evgeniy can handle this tomorrow.

Ok, here's another attempt that doesn't require storing the frame pointers.
In this case, we pass down the frame pointer we're looking for into the
unwind code and if we come across it while building up the trace, we immediately
empty the trace and start over, effectively popping the ASAN functions from
the trace.  If we never encounter the passed down frame pointer, then the code
will just behave as before.  Thoughts?

Peter


diff -urpN -X /home/bergner/cvs/dontdiff gcc-fsf-mainline-kcc/LAST_UPDATED gcc-fsf-mainline-asan/LAST_UPDATED
--- gcc-fsf-mainline-kcc/LAST_UPDATED	2012-11-20 11:40:17.232777673 -0600
+++ gcc-fsf-mainline-asan/LAST_UPDATED	2012-11-19 10:33:36.362778406 -0600
@@ -1,2 +1,2 @@
-Tue Nov 20 11:40:17 CST 2012
-Tue Nov 20 17:40:17 UTC 2012 (revision 193626)
+Mon Nov 19 10:33:36 CST 2012
+Mon Nov 19 16:33:36 UTC 2012 (revision 193626)
diff -urpN -X /home/bergner/cvs/dontdiff gcc-fsf-mainline-kcc/libsanitizer/asan/asan_linux.cc gcc-fsf-mainline-asan/libsanitizer/asan/asan_linux.cc
--- gcc-fsf-mainline-kcc/libsanitizer/asan/asan_linux.cc	2012-11-20 12:52:33.961664485 -0600
+++ gcc-fsf-mainline-asan/libsanitizer/asan/asan_linux.cc	2012-11-20 14:12:31.231751746 -0600
@@ -141,11 +141,27 @@ uptr Unwind_GetIP(struct _Unwind_Context
 #endif
 }
 
+uptr Unwind_GetBP(struct _Unwind_Context *ctx) {
+  return _Unwind_GetCFA(ctx);
+}
+
+struct Unwind_Trace_Info {
+  StackTrace *stack;
+  uptr bp;
+};
+
 _Unwind_Reason_Code Unwind_Trace(struct _Unwind_Context *ctx,
     void *param) {
-  StackTrace *b = (StackTrace*)param;
-  CHECK(b->size < b->max_size);
+  Unwind_Trace_Info *p = (Unwind_Trace_Info *)param;
+  StackTrace *b = p->stack;
   uptr pc = Unwind_GetIP(ctx);
+  if (Unwind_GetBP(ctx) == p->bp) {
+    // We just encountered the frame pointer we want to start
+    // our backtrace with, so empty the backtrace before adding
+    // this frame to the backtrace.
+    b->size = 0;
+  }
+  CHECK(b->size < b->max_size);
   b->trace[b->size++] = pc;
   if (b->size == b->max_size) return UNWIND_STOP;
   return UNWIND_CONTINUE;
@@ -157,9 +173,10 @@ void GetStackTrace(StackTrace *stack, up
   if ((max_s) > 1) {
     stack->max_size = max_s;
 #if defined(__arm__) || defined(__powerpc__) || defined(__powerpc64__)
-    _Unwind_Backtrace(Unwind_Trace, stack);
-    // Pop off the two ASAN functions from the backtrace.
-    stack->PopStackFrames(2);
+    Unwind_Trace_Info param;
+    param.stack = stack;
+    param.bp = bp;
+    _Unwind_Backtrace(Unwind_Trace, &param);
 #else
     if (!asan_inited) return;
     if (AsanThread *t = asanThreadRegistry().GetCurrent())