tool for padding/checksumming ax54g-payloads

Author: hsorbo

ax54g-pad.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+import argparse
+import struct
+import sys
+import zlib
+CKSUM_AX54G_FMT = struct.Struct(">I28x")
+
+BOOTLOADER_SIZE = 0x80000-0x2000
+KERNEL_SIZE = 0x180000
+
+
+def copy_into(dst, src, start):
+    for x in range(len(src)):
+        dst[start+x] = src[x]
+
+
+def main(args):
+    data = open(args.input, 'rb').read()
+    s = CKSUM_AX54G_FMT.size
+    if args.action == 'check':
+        exp = CKSUM_AX54G_FMT.unpack(data[-s:])[0]
+        got = zlib.adler32(data[:-s])
+        ok = "OK" if exp == got else "FAIL"
+        print("Checksum: {} expected 0x{:08x} got 0x{:08x}".format(ok, exp, got))
+    elif args.action == 'pad':
+        if len(data) in [KERNEL_SIZE, BOOTLOADER_SIZE]:
+            print("Already padded")
+            return
+        size = BOOTLOADER_SIZE if len(data) < BOOTLOADER_SIZE else KERNEL_SIZE
+        print("Assuming size 0x{:0x}".format(size))
+        out = bytearray([0]*size)
+        copy_into(out, data, 0)
+        cksum = zlib.adler32(bytes(out[:-s]))
+        CKSUM_AX54G_FMT.pack_into(out, size-s, cksum)
+        open(args.output, 'wb').write(out)
+
+    elif args.action == 'unpad':
+        if len(data) not in [KERNEL_SIZE, BOOTLOADER_SIZE]:
+            print("Probably not padded")
+        for x in range(len(data)-s-1, 0, -1):
+            if data[x] != 0x00:
+                print("{:08x}".format(x+1))
+                open(args.output, 'wb').write(data[:x+1])
+                break
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "-i", "--input", required=True, help="input file")
+    parser.add_argument(
+        "-o", "--output", required="check" not in sys.argv, help="output file")
+    parser.add_argument(
+        "-a", "--action",
+        choices=['pad', 'unpad', 'check'],
+        required=True,
+        help="output file")
+    main(parser.parse_args())