[asan] [SystemZ] Add slop for stack address detection.

On s390, siginfo reports the faulting address with page granularity -
we need to mask off the low bits of sp before comparison.

Differential Revision: http://reviews.llvm.org/D19112

llvm-svn: 266593

compiler-rt/lib/asan/asan_posix.cc

@@ -43,7 +43,15 @@ void AsanOnDeadlySignal(int signo, void *siginfo, void *context) {
   // Access at a reasonable offset above SP, or slightly below it (to account
   // for x86_64 or PowerPC redzone, ARM push of multiple registers, etc) is
   // probably a stack overflow.
+#ifdef __s390__
+  // On s390, the fault address in siginfo points to start of the page, not
+  // to the precise word that was accessed.  Mask off the low bits of sp to
+  // take it into account.
+  bool IsStackAccess = sig.addr >= (sig.sp & ~0xFFF) &&
+                       sig.addr < sig.sp + 0xFFFF;
+#else
   bool IsStackAccess = sig.addr + 512 > sig.sp && sig.addr < sig.sp + 0xFFFF;
+#endif
 
 #if __powerpc__
   // Large stack frames can be allocated with e.g.