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 <andrew.cooper3@citrix.com>
Signed-off-by: Jane Malalane <jane.malalane@citrix.com>
Reviewed-by: Ian Jackson <iwj@xenproject.org>
master commit: 3747a2bb67daa5a8baeff6cda57dc98a5ef79c3e
master date: 2021-07-30 10:52:46 +0100

diff --git a/xen/common/string.c b/xen/common/string.c
index af3d96ad0fa3a07fd4fc5ae48a2e859bbc080bcc..43624b1b4578d32d2c54db1acaf78b4c32b077c8 100644 (file)
--- a/xen/common/string.c
+++ b/xen/common/string.c
@@ -119,14 +119,16 @@ EXPORT_SYMBOL(strlcat);
  */
 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;
 }
 #endif
 
@@ -139,15 +141,17 @@ int (strcmp)(const char *cs, const char *ct)
  */
 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;
 }
 #endif