[PATCH] [MSan] Add __msan_unpoison_string() to the public interface.

[Sergey Matveev]

Hi eugenis,

Using __msan_unpoison() on null-terminated strings is awkward because
strlen() can't be called on a poisoned string. This case warrants a special
interface function.

http://llvm-reviews.chandlerc.com/D3135

Files:
  include/sanitizer/msan_interface.h
  lib/msan/msan_interceptors.cc
  lib/msan/msan_interface_internal.h
  test/msan/unpoison_string.cc

Index: include/sanitizer/msan_interface.h
===================================================================
--- include/sanitizer/msan_interface.h
+++ include/sanitizer/msan_interface.h
@@ -38,6 +38,10 @@
   /* Make memory region fully initialized (without changing its contents). */
   void __msan_unpoison(const volatile void *a, size_t size);
 
+  /* Make a null-terminated string fully initialized (without changing its
+     contents). */
+  void __msan_unpoison_string(const volatile char *a);
+
   /* Make memory region fully uninitialized (without changing its contents). */
   void __msan_poison(const volatile void *a, size_t size);
 
Index: lib/msan/msan_interceptors.cc
===================================================================
--- lib/msan/msan_interceptors.cc
+++ lib/msan/msan_interceptors.cc
@@ -1372,6 +1372,11 @@
   return res;
 }
 
+void __msan_unpoison_string(const char* s) {
+  if (!MEM_IS_APP(s)) return;
+  __msan_unpoison(s, REAL(strlen)(s) + 1);
+}
+
 namespace __msan {
 
 void CopyOrigin(void *dst, const void *src, uptr size, StackTrace *stack) {
Index: lib/msan/msan_interface_internal.h
===================================================================
--- lib/msan/msan_interface_internal.h
+++ lib/msan/msan_interface_internal.h
@@ -40,6 +40,8 @@
 SANITIZER_INTERFACE_ATTRIBUTE
 void __msan_unpoison(const void *a, uptr size);
 SANITIZER_INTERFACE_ATTRIBUTE
+void __msan_unpoison_string(const char *s);
+SANITIZER_INTERFACE_ATTRIBUTE
 void __msan_clear_and_unpoison(void *a, uptr size);
 SANITIZER_INTERFACE_ATTRIBUTE
 void* __msan_memcpy(void *dst, const void *src, uptr size);
Index: test/msan/unpoison_string.cc
===================================================================
--- /dev/null
+++ test/msan/unpoison_string.cc
@@ -0,0 +1,15 @@
+// RUN: %clangxx_msan -fsanitize-memory-track-origins -m64 -O0 %s -o %t
+// RUN: %t
+// RUN: %clangxx_msan -fsanitize-memory-track-origins -m64 -O3 %s -o %t
+// RUN: %t
+
+#include <assert.h>
+#include <string.h>
+#include <sanitizer/msan_interface.h>
+
+int main(int argc, char **argv) {
+  char s[20] = "string";
+  __msan_poison(s, 20 * sizeof(char));
+  __msan_unpoison_string(s);
+  assert(__msan_test_shadow(s, 20 * sizeof(char)) == strlen("string") + 1);
+}
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