Callgrind: fix segfault when dumping after toggling instrumentation mode

This bug shows up when callgrind dumps data of a BB with 0 instructions
(the segfault only appears on x86_64; for x86 we were "lucky").

"BB with 0 instructions" happens when you switch on instrumentation
(and callgrinds call graph tracing starts with an emtpy shadow call
stack) in the middle of a run: Whenever the shadow callstack
is empty, but callgrind sees a return instruction (ie. a shadow
callstack underrun), it creates an artifical BB which is faked to
have called the function we are returning from.
This way, the call arc is noted and will appear in the dump.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@6053

diff --git a/callgrind/global.h b/callgrind/global.h
index f6190a206c7785bd874221901d084078ab8ab6b3..0079b4d3a0a75c1d7fb94399f4d719cbe43cc5ad 100644 (file)
--- a/callgrind/global.h
+++ b/callgrind/global.h
@@ -688,7 +688,8 @@ void CLG_(delete_bb)(Addr addr);
 static __inline__ Addr bb_addr(BB* bb)
  { return bb->offset + bb->obj->offset; }
 static __inline__ Addr bb_jmpaddr(BB* bb)
- { return bb->instr[bb->instr_count-1].instr_offset + bb->offset + bb->obj->offset; }
+ { UInt off = (bb->instr_count > 0) ? bb->instr[bb->instr_count-1].instr_offset : 0;
+   return off + bb->offset + bb->obj->offset; }
 
 /* from fn.c */
 void CLG_(init_fn_array)(fn_array*);