== kernel source identity (guest /usr/src vs repo sys/) ==
370024243 4183 /usr/src/sys/libkern/strtol.c
3544205135 3234 /usr/src/sys/libkern/strtoul.c
cksum: illegal option -- a
usage: cksum [-o 1 | 2 | 3] [file ...]
       sum [file ...]
== generating userland-compilable copies via sed (no hand edits) ==
k_strtol_fix.c: 1 isxdigit guard site(s) (expect 1)
k_strtoul_fix.c: 1 isxdigit guard site(s) (expect 1)
== diff of fix vs baseline (must be ONLY the guard) ==
--- k_strtol.c	2026-10-10 07:50:51.045006000 +0000
+++ k_strtol_fix.c	2026-10-10 07:50:51.055082000 +0000
@@ -43,7 +43,7 @@
  * alphabets and digits are each contiguous.
  */
 long
-k_strtol(const char *nptr, char **endptr, int base)
+k_strtol_fix(const char *nptr, char **endptr, int base)
 {
 	const char *s = nptr;
 	unsigned long acc;
@@ -65,7 +65,7 @@
 	} else if (c == '+')
 		c = *s++;
 	if ((base == 0 || base == 16) &&
-	    c == '0' && (*s == 'x' || *s == 'X')) {
+	    c == '0' && (*s == 'x' || *s == 'X') && isxdigit((unsigned char)s[1])) {
 		c = s[1];
 		s += 2;
 		base = 16;
--- k_strtoul.c	2026-10-10 07:50:51.055082000 +0000
+++ k_strtoul_fix.c	2026-10-10 07:50:51.065120000 +0000
@@ -43,7 +43,7 @@
  * alphabets and digits are each contiguous.
  */
 unsigned long
-k_strtoul(const char *nptr, char **endptr, int base)
+k_strtoul_fix(const char *nptr, char **endptr, int base)
 {
 	const char *s = nptr;
 	unsigned long acc;
@@ -63,7 +63,7 @@
 	} else if (c == '+')
 		c = *s++;
 	if ((base == 0 || base == 16) &&
-	    c == '0' && (*s == 'x' || *s == 'X')) {
+	    c == '0' && (*s == 'x' || *s == 'X') && isxdigit((unsigned char)s[1])) {
 		c = s[1];
 		s += 2;
 		base = 16;
== compile ==
build OK: /tmp/df5703/diffharness