[msan] Allow strlen() (and similar functions) of shadow memory.

llvm-svn: 196572

compiler-rt/lib/msan/lit_tests/strlen_of_shadow.cc

@@ -0,0 +1,24 @@
+// RUN: %clangxx_msan -m64 -O0 %s -o %t && %t
+
+// Check that strlen() and similar intercepted functions can be called on shadow
+// memory.
+
+#include <assert.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+const char *mem_to_shadow(const char *p) {
+  return (char *)((uintptr_t)p & ~0x400000000000ULL);
+}
+
+int main(void) {
+  const char *s = "abcdef";
+  assert(strlen(s) == 6);
+  assert(strlen(mem_to_shadow(s)) == 0);
+
+  char *t = new char[42];
+  t[41] = 0;
+  assert(strlen(mem_to_shadow(t)) == 41);
+  return 0;
+}

compiler-rt/lib/msan/msan.cc

@@ -398,7 +398,8 @@ void __msan_print_param_shadow() {
 }
 
 sptr __msan_test_shadow(const void *x, uptr size) {
-  unsigned char *s = (unsigned char*)MEM_TO_SHADOW((uptr)x);
+  if (!MEM_IS_APP(x)) return -1;
+  unsigned char *s = (unsigned char *)MEM_TO_SHADOW((uptr)x);
   for (uptr i = 0; i < size; ++i)
     if (s[i])
       return i;