[PATCH] [Msan] Fix the if_indextoname.cc test to pass on FreeBSD

[Viktor Kutuzov]

Hi kcc, samsonov, eugenis,

On FreeBSD if_indextoname() leverages strncpy() that unpoisons the whole name buffer, what in turn results in the assertion following the if_indextoname() call to fail:
```
  if (!if_indextoname(1, ifname)) {
    ...
  }
  assert(strlen(ifname) + 1 == __msan_test_shadow(ifname, sizeof(ifname)));
```

http://reviews.llvm.org/D9456

Files:
  lib/msan/msan_interceptors.cc
  lib/sanitizer_common/sanitizer_platform_interceptors.h

Index: lib/msan/msan_interceptors.cc
===================================================================
--- lib/msan/msan_interceptors.cc
+++ lib/msan/msan_interceptors.cc
@@ -309,7 +309,8 @@
     copy_size++;  // trailing \0
   char *res = REAL(strncpy)(dest, src, n);  // NOLINT
   CopyShadowAndOrigin(dest, src, copy_size, &stack);
-  __msan_unpoison(dest + copy_size, n - copy_size);
+  if (!IsInInterceptorScope())
+    __msan_unpoison(dest + copy_size, n - copy_size);
   return res;
 }
 
Index: lib/sanitizer_common/sanitizer_platform_interceptors.h
===================================================================
--- lib/sanitizer_common/sanitizer_platform_interceptors.h
+++ lib/sanitizer_common/sanitizer_platform_interceptors.h
@@ -223,7 +223,8 @@
 #define SANITIZER_INTERCEPT_GETXATTR SI_LINUX
 #define SANITIZER_INTERCEPT_GETRESID SI_LINUX
 #define SANITIZER_INTERCEPT_GETIFADDRS SI_LINUX_NOT_ANDROID || SI_MAC
-#define SANITIZER_INTERCEPT_IF_INDEXTONAME SI_LINUX_NOT_ANDROID || SI_MAC
+#define SANITIZER_INTERCEPT_IF_INDEXTONAME \
+  SI_FREEBSD || SI_LINUX_NOT_ANDROID || SI_MAC
 #define SANITIZER_INTERCEPT_CAPGET SI_LINUX_NOT_ANDROID
 #define SANITIZER_INTERCEPT_AEABI_MEM SI_LINUX && defined(__arm__)
 #define SANITIZER_INTERCEPT___BZERO SI_MAC

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