boot: bootutil: swap_offset: Fix maximum application size

Fixes this functionality to have the maximum allowable application
size

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

Author: nordicjm

boot/bootutil/src/swap_offset.c

@@ -307,23 +307,26 @@ static int app_max_sectors(struct boot_loader_state *state)
     uint32_t sz = 0;
     uint32_t sector_sz;
     uint32_t trailer_sz;
-    uint32_t first_trailer_idx;
+    uint32_t available_sectors_pri;
+    uint32_t available_sectors_sec;
+    uint32_t trailer_sectors = 0;
 
     sector_sz = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, 0);
     trailer_sz = boot_trailer_sz(BOOT_WRITE_SZ(state));
-    first_trailer_idx = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT);
 
     while (1) {
         sz += sector_sz;
+        ++trailer_sectors;
 
         if  (sz >= trailer_sz) {
             break;
         }
-
-        first_trailer_idx--;
     }
 
-    return first_trailer_idx;
+    available_sectors_pri = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT) - trailer_sectors;
+    available_sectors_sec = boot_img_num_sectors(state, BOOT_SECONDARY_SLOT) - 1;
+
+    return (available_sectors_pri < available_sectors_sec ? available_sectors_pri : available_sectors_sec);
 }
 
 int boot_slots_compatible(struct boot_loader_state *state)
@@ -333,34 +336,35 @@ int boot_slots_compatible(struct boot_loader_state *state)
     size_t sector_sz_pri = 0;
     size_t sector_sz_sec = 0;
     size_t i;
-    size_t num_usable_sectors_pri;
+    size_t num_usable_sectors;
 
     num_sectors_pri = boot_img_num_sectors(state, BOOT_PRIMARY_SLOT);
     num_sectors_sec = boot_img_num_sectors(state, BOOT_SECONDARY_SLOT);
-    num_usable_sectors_pri = app_max_sectors(state);
+    num_usable_sectors = app_max_sectors(state);
 
-    if ((num_sectors_pri != num_sectors_sec) &&
-            ((num_sectors_pri + 1) != num_sectors_sec) &&
-            ((num_usable_sectors_pri + 1) != (num_sectors_sec))) {
+    if (num_sectors_pri != num_sectors_sec &&
+        (num_sectors_pri + 1) != num_sectors_sec &&
+        num_usable_sectors != (num_sectors_sec - 1)) {
         BOOT_LOG_WRN("Cannot upgrade: not a compatible amount of sectors");
-        BOOT_LOG_DBG("slot0 sectors: %d, slot1 sectors: %d, usable slot0 sectors: %d",
+        BOOT_LOG_DBG("slot0 sectors: %d, slot1 sectors: %d, usable sectors: %d",
                      (int)num_sectors_pri, (int)num_sectors_sec,
-                     (int)(num_usable_sectors_pri - 1));
+                     (int)(num_usable_sectors));
         return 0;
     } else if (num_sectors_pri > BOOT_MAX_IMG_SECTORS) {
         BOOT_LOG_WRN("Cannot upgrade: more sectors than allowed");
         return 0;
     }
 
-    if ((num_usable_sectors_pri + 1) != num_sectors_sec) {
+    if ((num_usable_sectors + 1) != num_sectors_sec) {
         BOOT_LOG_DBG("Non-optimal sector distribution, slot0 has %d usable sectors "
-                     "but slot1 has %d usable sectors", (int)(num_usable_sectors_pri),
+                     "but slot1 has %d usable sectors", (int)(num_usable_sectors),
                      ((int)num_sectors_sec - 1));
     }
 
-    for (i = 0; i < num_sectors_pri; i++) {
+    for (i = 0; i < num_usable_sectors; i++) {
         sector_sz_pri = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, i);
         sector_sz_sec = boot_img_sector_size(state, BOOT_SECONDARY_SLOT, i);
+
         if (sector_sz_pri != sector_sz_sec) {
             BOOT_LOG_WRN("Cannot upgrade: not same sector layout");
             return 0;
@@ -726,19 +730,10 @@ void swap_run(struct boot_loader_state *state, struct boot_status *bs,
 int app_max_size(struct boot_loader_state *state)
 {
     uint32_t sector_sz_primary;
-    uint32_t sector_sz_secondary;
-    uint32_t sz_primary;
-    uint32_t sz_secondary;
 
     sector_sz_primary = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, 0);
-    sector_sz_secondary = boot_img_sector_size(state, BOOT_SECONDARY_SLOT, 0);
-
-    /* Account for image flags and move sector */
-    sz_primary = app_max_sectors(state) * sector_sz_primary;
-    sz_secondary = boot_img_num_sectors(state, BOOT_SECONDARY_SLOT) * sector_sz_secondary -
-                    sector_sz_primary;
 
-    return (sz_primary <= sz_secondary ? sz_primary : sz_secondary);
+    return app_max_sectors(state) * sector_sz_primary;
 }
 
 /* Compute the total size of the given image. Includes the size of the TLVs. */