nfc-tools
ARM issue desfire_crc32 wrong direction
Dear,
found an issue how arm interprets direct assignment of crc in the buffer
*((uint32_t *)(crc)) = htole32(desfire_crc);
On non-arm this does as expected at the position of crc pointer CRC is added to the right side of the buffer crc, crc+1, crc+2, crc+3
On the ARM that we are using things are opposite crc is added to the left of the buffer crc, crc-1,crc-2,crc-3 :)
We corrected the code with memcpy:
memcpy(crc, &htole32(desfire_crc), sizeof(uint32_t));
Hope this helps someone
Uh… Another option would be to use binary operators to make all this obvious:
crc[0] = desfire_crc & 0x000000ff;
crc[1] = (desfire_crc & 0x0000ff00) >> 8;
crc[2] = (desfire_crc & 0x00ff0000) >> 16;
crc[3] = (desfire_crc & 0xff000000) >> 24;
(unless it is the other way arroud…). Maybe a bit more readable and I would be surprised if the compiler does not optimize both snippets the same way.
Would you mind filling-in a Pull Request?
On the ARM that we are using things are opposite crc is added to the left of the buffer crc, crc-1,crc-2,crc-3 :)
I'm guessing the pointer crc isn't aligned on a 32-bit boundary. Classic undefined-behavior bug.
What file is this in?
