lib/string: Add standard strstr() function

Adding implementation of standard library strstr()

See https://review.coreboot.org/c/coreboot/+/43741 for context.

Change-Id: I63e26e98ed2dd15542f81c0a3a5e353bb93b7350
Signed-off-by: jbk@chromium.org
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44085
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
diff --git a/src/lib/string.c b/src/lib/string.c
index e8f72a2..9677520 100644
--- a/src/lib/string.c
+++ b/src/lib/string.c
@@ -163,6 +163,16 @@
 	return ret;
 }
 
+char *strstr(const char *haystack, const char *needle)
+{
+	size_t needle_len = strlen(needle);
+	for (; *haystack; haystack++) {
+		if (!strncmp(haystack, needle, needle_len))
+			return (char *)haystack;
+	}
+	return NULL;
+}
+
 char *strtok_r(char *str, const char *delim, char **ptr)
 {
 	char *start;