[PATCH 4/5] Use volatile trick for explicit_bzero

[roucaries . bastien]

From: Bastien Roucariès <address@hidden>

Use a volatile pointer to memset function to avoid dead end optimization

Signed-off-by: Bastien Roucariès <address@hidden>
---
 lib/explicit_bzero.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/lib/explicit_bzero.c b/lib/explicit_bzero.c
index 21bbd67e8..59215852c 100644
--- a/lib/explicit_bzero.c
+++ b/lib/explicit_bzero.c
@@ -43,6 +43,10 @@
 # undef explicit_bzero
 #endif
 
+#if !defined __GNUC__
+static void * (* const volatile volatile_memset)(void *, int, size_t) = memset;
+#endif
+
 /* Set LEN bytes of S to 0.  The compiler will not delete a call to
    this function, even if S is dead after the call.  */
 void
@@ -54,17 +58,17 @@ explicit_bzero (void *s, size_t len)
   (void) memset_s(s,len,'\0',len);
 #elif HAVE_SECUREZEROMEMORY
   (void) SecureZeroMemory(s,len);
-#else
-  memset (s, '\0', len);
-#if defined __GNUC__
+#elif defined __GNUC__
+  (void) memset (s, '\0', len);
 #   if !defined __clang__
     /* Compiler barrier.  */
-    asm volatile ("" ::: "memory");
+  asm volatile ("" ::: "memory");
 #  else
    /* https://bugs.llvm.org/show_bug.cgi?id=15495#c11 */
   __asm__ volatile("" : : "g"(s) : "memory");
 #  endif
+#else
+  (void) volatile_memset(s,'\0',len);
 #endif
-
 #endif
 }
-- 
2.25.1