components: factor the offset-table uname fingerprint into a helper

qemu_tcg_iret and entrybleed each composed "<release> <version>" and matched it
against a per-build offset table, but only qemu_tcg_iret trimmed the trailing
space a 64-char-clipped Ubuntu HWE uname can leave. Add kasld_uname_fingerprint()
(compose + trim) beside kasld_uname in sysroot.h and call it from both; each
keeps its own uname fetch and failure policy, so only the compose+trim is shared
and entrybleed picks up the trim.

Author: bcoles

src/components/entrybleed.c

@@ -280,8 +280,7 @@ static int detect_kernel_version(void) {
     exit(kasld_disp_absent("not a 64-bit kernel"));
   }
 
-  snprintf(kernel_version, KERNEL_VERSION_SIZE_BUFFER, "%s %s", u.release,
-           u.version);
+  kasld_uname_fingerprint(kernel_version, KERNEL_VERSION_SIZE_BUFFER, &u);
 
   unsigned long i;
   for (i = 0; i < ARRAY_SIZE(offsets); i++) {

src/components/qemu_tcg_iret.c

@@ -162,21 +162,17 @@ static const struct kernel_info offsets[] = {
 
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
 
-/* Index into offsets[] whose full uname matches this kernel, or -1. Trailing
- * whitespace is trimmed before comparing: a long Ubuntu HWE version clipped at
- * utsname's 64-char field can end on a space, and the table stores fingerprints
- * trimmed the same way, so the live uname is trimmed to match. */
+/* Index into offsets[] whose full uname matches this kernel, or -1. The
+ * fingerprint (compose + trailing-space trim) is built by
+ * kasld_uname_fingerprint(); see its comment for why the trim matters. */
 static int match_known_kernel(void) {
   struct utsname u;
   char v[512];
-  size_t n;
   unsigned long i;
 
   if (kasld_uname(&u) != 0)
     return -1;
-  snprintf(v, sizeof(v), "%s %s", u.release, u.version);
-  for (n = strlen(v); n > 0 && v[n - 1] == ' '; n--)
-    v[n - 1] = '\0';
+  kasld_uname_fingerprint(v, sizeof(v), &u);
   for (i = 0; i < ARRAY_SIZE(offsets); i++)
     if (strcmp(v, offsets[i].kernel_version) == 0)
       return (int)i;

src/include/kasld/sysroot.h

@@ -146,4 +146,18 @@ __attribute__((unused)) static int kasld_uname(struct utsname *u) {
   return rc;
 }
 
+/* Compose "<release> <version>" into buf and trim trailing spaces. Offset-table
+ * components match this full-uname build fingerprint against per-build entries;
+ * a long Ubuntu HWE version is clipped at utsname.version's 64-char field and
+ * can end on a space, so trimming keeps the live string equal to the (also
+ * trimmed) stored fingerprint. The caller passes the utsname (from kasld_uname)
+ * so each component keeps its own uname fetch and failure policy. */
+__attribute__((unused)) static void
+kasld_uname_fingerprint(char *buf, size_t n, const struct utsname *u) {
+  size_t i;
+  snprintf(buf, n, "%s %s", u->release, u->version);
+  for (i = strlen(buf); i > 0 && buf[i - 1] == ' '; i--)
+    buf[i - 1] = '\0';
+}
+
 #endif /* KASLD_SYSROOT_H */