1 files changed, 91 insertions, 0 deletions
diff --git a/missing/explicit_bzero.c b/missing/explicit_bzero.c
new file mode 100644
index 0000000000..59417e158e
--- /dev/null
+++ b/missing/explicit_bzero.c
@@ -0,0 +1,91 @@
+#ifndef __STDC_WANT_LIB_EXT1__
+#define __STDC_WANT_LIB_EXT1__ 1 /* for memset_s() */
+#endif
+
+#include "ruby/missing.h"
+#include <string.h>
+
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
+/* Similar to bzero(), but has a guarantee not to be eliminated from compiler
+   optimization. */
+
+/* OS support note:
+ * BSDs have explicit_bzero().
+ * macOS has memset_s().
+ * Windows has SecureZeroMemory() since XP.
+ * Linux has explicit_bzero() since glibc 2.25, musl libc 1.1.20.
+ */
+
+/*
+ * Following URL explains why memset_s is added to the standard.
+ * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1381.pdf
+ */
+
+#ifndef FUNC_UNOPTIMIZED
+# define FUNC_UNOPTIMIZED(x) x
+#endif
+
+#undef explicit_bzero
+#ifndef HAVE_EXPLICIT_BZERO
+ #ifdef HAVE_EXPLICIT_MEMSET
+void
+explicit_bzero(void *b, size_t len)
+{
+    (void)explicit_memset(b, 0, len);
+}
+ #elif defined HAVE_MEMSET_S
+void
+explicit_bzero(void *b, size_t len)
+{
+    memset_s(b, len, 0, len);
+}
+ #elif defined SecureZeroMemory
+void
+explicit_bzero(void *b, size_t len)
+{
+    SecureZeroMemory(b, len);
+}
+
+ #elif defined HAVE_FUNC_WEAK
+
+/* A weak function never be optimized away. Even if nobody uses it. */
+WEAK(void ruby_explicit_bzero_hook_unused(void *buf, size_t len));
+void
+ruby_explicit_bzero_hook_unused(void *buf, size_t len)
+{
+}
+
+void
+explicit_bzero(void *b, size_t len)
+{
+    memset(b, 0, len);
+    ruby_explicit_bzero_hook_unused(b, len);
+}
+
+ #else /* Your OS have no capability. Sigh. */
+
+FUNC_UNOPTIMIZED(void explicit_bzero(void *b, size_t len));
+#undef explicit_bzero
+
+void
+explicit_bzero(void *b, size_t len)
+{
+    /*
+     * volatile is not enough if the compiler has an LTO (link time
+     * optimization). At least, the standard provides no guarantee.
+     * However, gcc and major other compilers never optimize a volatile
+     * variable away. So, using volatile is practically ok.
+     */
+    volatile char* p = (volatile char*)b;
+
+    while(len) {
+	*p = 0;
+	p++;
+	len--;
+    }
+}
+ #endif
+#endif /* HAVE_EXPLICIT_BZERO */