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Index: lib/libc/string/bzero.3
===================================================================
--- lib/libc/string/bzero.3
+++ lib/libc/string/bzero.3
@@ -62,9 +62,9 @@
.Pp
The
.Fn explicit_bzero
-variant behaves the same, but will not be removed by a compiler's dead store
-optimization pass, making it useful for clearing sensitive memory such as a
-password.
+variant is the same, but has correct flags to force the call to occur,
+no matter if the compiler thinks it is pointless, or not, making it
+useful for clearing sensitive memory such as a password.
.Sh SEE ALSO
.Xr memset 3 ,
.Xr swab 3
Index: sys/libkern/explicit_bzero.c
===================================================================
--- sys/libkern/explicit_bzero.c
+++ sys/libkern/explicit_bzero.c
@@ -13,16 +13,42 @@
#include <string.h>
#endif /* _KERNEL */
-__attribute__((weak)) void __explicit_bzero_hook(void *, size_t);
-__attribute__((weak)) void
-__explicit_bzero_hook(void *buf, size_t len)
-{
-}
+#if __clang__
+ /*
+ * http://clang.llvm.org/docs/LanguageExtensions.html#feature-checking-macros
+ * http://lists.cs.uiuc.edu/pipermail/cfe-dev/2014-December/040627.html
+ */
+ #if __has_attribute( noinline ) /* && __has_attribute( optnone ) */
+ #define NOOPT /* __attribute__ (( optnone )) */
+ #define NOINLINE __attribute__ (( noinline ))
+ #else
+ #error "require clang with noinline and optnone attributes"
+ #endif
+#elif __GNUC__
+ /*
+ * http://gcc.gnu.org/onlinedocs/gcc/Function-Specific-Option-Pragmas.html
+ * http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
+ */
+ #if __GNUC__ > 4 || ( __GNUC__ == 4 && __GNUC_MINOR__ >= 4 )
+ #define NOOPT __attribute__ (( optimize( 0 ) ))
+ #define NOINLINE __attribute__ (( noinline ))
+ #else
+ #error "require gcc >= 4.4"
+ #endif
+#else
+ #error "unrecognised compiler"
+ explode
+#endif
-void
+NOOPT NOINLINE void
explicit_bzero(void *buf, size_t len)
{
- memset(buf, 0, len);
- __explicit_bzero_hook(buf, len);
+ size_t i;
+ unsigned char *p = buf;
+
+ for (i = 0; i < len; i++) {
+ p[i] = 0;
+ }
}
+

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