fix aliasing-based undefined behavior in string functions

use the GNU C may_alias attribute if available, and fallback to naive
byte-by-byte loops if __GNUC__ is not defined.

this patch has been written to minimize changes so that history
remains reviewable; it does not attempt to bring the affected code
into a more consistent or elegant form.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/string/strlen.c b/src/string/strlen.c
index 929ddcbc..309990f0 100644
--- a/src/string/strlen.c
+++ b/src/string/strlen.c
@@ -10,9 +10,13 @@
 size_t strlen(const char *s)
 {
 	const char *a = s;
-	const size_t *w;
+#ifdef __GNUC__
+	typedef size_t __attribute__((__may_alias__)) word;
+	const word *w;
 	for (; (uintptr_t)s % ALIGN; s++) if (!*s) return s-a;
 	for (w = (const void *)s; !HASZERO(*w); w++);
-	for (s = (const void *)w; *s; s++);
+	s = (const void *)w;
+#endif
+	for (; *s; s++);
 	return s-a;
 }