avrdude/tools/bootloader-hash

#!/bin/bash

# published under GNU General Public License, version 3 (GPL-3.0)
# author Stefan Rueger, 2022
#
# Recursivly find in the current directory intel .hex files, which are
# presumed to be bootloaders; create their hash table entry for urclock.c
#
# Background. This bash script computes the hash-sum of stk500v1 bootloaders
# to ease the guesswork of AVRDUDE's -c urclock programmer. Urclock is
# compatible with -c arduino, but needs to know the size of the bootloader to
# protect it *externally* from being overwritten. In contrast to urboot,
# optiboot et al binaries do not advertise their size and properties. Hence,
# urclock.c maintains a table with hash-sums of popular bootloaders that are
# out there in the wild, so the user doesn't have to know, let alone specify,
# the size of the bootloader on their devices. This utility computes the
# table entry from a .hex files in the directory.
#
# Example:
# $ git clone git@github.com:MCUdude/optiboot_flash.git
# $ ./bootloader-hash

progname=$(basename $0)

hash srec_cat 2>/dev/null || { echo $progname: package srecord is needed, try apt install srecord; exit; }
hash cc 2>/dev/null || { echo $progname: need a C compiler; exit; }

tmp=$(mktemp "$progname.XXXXXX")
trap "rm -f $tmp $tmp.[ch]" EXIT

cat >$tmp.c <<END
// published under GNU General Public License, version 3 (GPL-3.0)
// meta-autor Stefan Rueger, 2022

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#include "$tmp.h"

// https://en.wikipedia.org/wiki/Jenkins_hash_function
uint32_t jenkins_hash(const uint8_t* key, size_t length) {
  size_t i = 0;
  uint32_t hash = 0;

  while (i != length) {
    hash += key[i++];
    hash += hash << 10;
    hash ^= hash >> 6;
  }
  hash += hash << 3;
  hash ^= hash >> 11;
  hash += hash << 15;

  return hash;
}


int main(int argc, char **argv) {
  unsigned char reverse[4096];

  if(argc != 2 || !argv[1])
    exit(1);

  int len, addr, end, flashsize, bi, ri;
  char *base = strrchr(argv[1], '/');
  base = base? base+1: argv[1];

  memset(reverse, 0, sizeof reverse);

  flashsize = bootloader_finish;
  while(flashsize & (flashsize-1))
    flashsize++;

  int N = sizeof bootloader_length_of_sections/sizeof*bootloader_length_of_sections;

  ri = 0;                       // buffer index
  bi = sizeof bootloader-1;     // index in bootloader[] array, top to bottom
  end = flashsize;
  for(int i=N-1; i >= 0; i--) {
    len = bootloader_length_of_sections[i];
    addr = bootloader_address[i];
    if(addr == 0)
      break;
    if(addr + len > end) {
      printf("inconsistent %d + %d > %d\n", addr, len, end);
      exit(1);
    }

    int nff = end-addr-len;
    if(ri+nff <= (int) sizeof reverse)
      memset(reverse+ri, 0xff, nff);
    else {
      printf("buffer too small %d + %d > %d\n", ri, nff, (int) sizeof reverse);
      exit(1);
    }
    ri += nff;

    for(int n=len; n; n--) {
      if(ri >= (int) sizeof reverse)
        goto done;
      reverse[ri] = bootloader[bi];
      ri++;
      bi--;
    }
    end = addr;
  }
  
done:
  ;
  printf("    { %4d, %d, 0x%08x, 0x%08x }, // %s\n", ri, 
    strstr(base, "bigboot") || strstr(base, "BIGBOOT"),
    jenkins_hash(reverse, 256), jenkins_hash(reverse, ri), base);
}
END


for hn in $(find . -iname \*.hex -type f); do
  srec_cat "$hn" -intel -o "$tmp.h" -c-array bootloader -c_compressed -line_length 96
  cc $tmp.c -o $tmp
  ./$tmp $hn
done