cbtable.c: Factor out lb_header_validation logic

Write a pure function for the header validation logic, it is
easier to unit-test.

Change-Id: Ia288bcbc5c371329952a6efba30ccf0e18965a3d
Signed-off-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/37238
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

1 files changed, 20 insertions, 12 deletions

diff --git a/cbtable.c b/cbtable.c
index bdf53ce38..669a4619d 100644
--- a/cbtable.c
+++ b/cbtable.c
@@ -151,6 +151,25 @@ static unsigned int count_lb_records(struct lb_header *head)
 	return count;
 }
 
+static int lb_header_valid(struct lb_header *head, unsigned long addr)
+{
+	if (memcmp(head->signature, "LBIO", 4) != 0)
+		return 0;
+	msg_pdbg("Found candidate at: %08lx-%08lx\n",
+		     addr, addr + sizeof(*head) + head->table_bytes);
+	if (head->header_bytes != sizeof(*head)) {
+		msg_perr("Header bytes of %d are incorrect.\n",
+			head->header_bytes);
+		return 0;
+	}
+	if (compute_checksum((uint8_t *) head, sizeof(*head)) != 0) {
+		msg_perr("Bad header checksum.\n");
+		return 0;
+	}
+
+	return 1;
+}
+
 static struct lb_header *find_lb_table(void *base, unsigned long start,
 				       unsigned long end)
 {
@@ -162,24 +181,13 @@ static struct lb_header *find_lb_table(void *base, unsigned long start,
 		    (struct lb_header *)(((char *)base) + addr);
 		struct lb_record *recs =
 		    (struct lb_record *)(((char *)base) + addr + sizeof(*head));
-		if (memcmp(head->signature, "LBIO", 4) != 0)
-			continue;
-		msg_pdbg("Found candidate at: %08lx-%08lx\n",
-			     addr, addr + head->table_bytes);
-		if (head->header_bytes != sizeof(*head)) {
-			msg_perr("Header bytes of %d are incorrect.\n",
-				head->header_bytes);
+		if (!lb_header_valid(head, addr))
 			continue;
-		}
 		if (count_lb_records(head) != head->table_entries) {
 			msg_perr("Bad record count: %d.\n",
 				head->table_entries);
 			continue;
 		}
-		if (compute_checksum((uint8_t *) head, sizeof(*head)) != 0) {
-			msg_perr("Bad header checksum.\n");
-			continue;
-		}
 		if (compute_checksum(recs, head->table_bytes)
 		    != head->table_checksum) {
 			msg_perr("Bad table checksum: %04x.\n",