xen/lib: Fix strcmp() and strncmp()

The C standard requires that each character be compared as unsigned char. Xen's current behaviour compares as signed char, which changes the answer when chars with a value greater than 0x7f are used. Suggested-by: Andrew Cooper <[email protected]> Signed-off-by: Jane Malalane <[email protected]> Reviewed-by: Ian Jackson <[email protected]>
vireshk · Jul 30, 2021 · 3747a2b · 3747a2b
1 parent 58ad654
commit 3747a2b
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Showing 2 changed files with 10 additions and 6 deletions.
diff --git a/xen/lib/strcmp.c b/xen/lib/strcmp.c
@@ -11,14 +11,16 @@
  */
 int (strcmp)(const char *cs, const char *ct)
 {
-	register signed char __res;
+	unsigned char *csu = (unsigned char *)cs;
+	unsigned char *ctu = (unsigned char *)ct;
+	int res;
 
 	while (1) {
-		if ((__res = *cs - *ct++) != 0 || !*cs++)
+		if ((res = *csu - *ctu++) != 0 || !*csu++)
 			break;
 	}
 
-	return __res;
+	return res;
 }
 
 /*

diff --git a/xen/lib/strncmp.c b/xen/lib/strncmp.c
@@ -12,15 +12,17 @@
  */
 int (strncmp)(const char *cs, const char *ct, size_t count)
 {
-	register signed char __res = 0;
+	unsigned char *csu = (unsigned char *)cs;
+	unsigned char *ctu = (unsigned char *)ct;
+	int res = 0;
 
 	while (count) {
-		if ((__res = *cs - *ct++) != 0 || !*cs++)
+		if ((res = *csu - *ctu++) != 0 || !*csu++)
 			break;
 		count--;
 	}
 
-	return __res;
+	return res;
 }
 
 /*