bootutil: Fix swap move max app size calculation

This calculation failed to take into consideration the additional
sector needed for the swap move part of the upgrade process

Signed-off-by: Jamie McCrae <[email protected]>

Author: nordicjm

boot/bootutil/src/swap_move.c

@@ -577,11 +577,19 @@ swap_run(struct boot_loader_state *state, struct boot_status *bs,
 
 int app_max_size(struct boot_loader_state *state)
 {
-    uint32_t sector_sz;
+    uint32_t sector_sz_primary;
+    uint32_t sector_sz_secondary;
+    uint32_t sz_primary;
+    uint32_t sz_secondary;
 
-    sector_sz = boot_img_sector_size(state, BOOT_PRIMARY_SLOT, 0);
+    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 - sector_sz_primary;
+    sz_secondary = boot_img_num_sectors(state, BOOT_SECONDARY_SLOT) * sector_sz_secondary;
 
-    return (app_max_sectors(state) * sector_sz);
+    return (sz_primary <= sz_secondary ? sz_primary : sz_secondary);
 }
 
 #endif