diff --git a/lib/string.c b/lib/string.c
index 4fb566ea610ffd..1718f96e8082de 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -880,3 +880,30 @@ void *memchr_inv(const void *start, int c, size_t bytes)
 	return check_bytes8(start, value, bytes % 8);
 }
 EXPORT_SYMBOL(memchr_inv);
+
+static int sign(int x)
+{
+	return (x > 0) - (x < 0);
+}
+
+static int test_xxxcmp(void)
+{
+	char a[2], b[2];
+	int i, j;
+
+	a[1] = b[1] = 0;
+	for (i = 0; i < 256; ++i) {
+		a[0] = i;
+		for (j = 0; j < 256; ++j) {
+			b[0] = j;
+			WARN_ONCE(sign(strcmp(a, b)) != sign(i - j),
+				  "strcmp() broken for (%2ph, %2ph)\n", a, b);
+			WARN_ONCE(sign(memcmp(a, b, 2)) != sign(i - j),
+				  "memcmp() broken for (%2ph, %2ph)\n", a, b);
+			WARN_ONCE(sign(strncmp(a, b, 2)) != sign(i - j),
+				  "strncmp() broken for (%2ph, %2ph)\n", a, b);
+		}
+	}
+	return 0;
+}
+late_initcall(test_xxxcmp);