// calculate and embed MD5 digest
 {
 fprintf(stderr, "Embedding MD5 digest\n");
 unsigned long digest_md5_offset = 0;
 unsigned long digest_md5_length = 0;
 bool rv = appimage_get_elf_section_offset_and_length(destination, ".digest_md5", &digest_md5_offset, &digest_md5_length);
 if (!rv || digest_md5_offset == 0 || digest_md5_length == 0) {
 die("Could not find section .digest_md5 in runtime");
 }
 static const unsigned long section_size = 16;
 if (digest_md5_length < section_size) {
 fprintf(
 stderr,
 ".digest_md5 section in runtime's ELF header is too small"
 "(found %lu bytes, minimum required: %lu bytes)\n",
 digest_md5_length, section_size
 );
 exit(1);
 }
 char digest_buffer[section_size];
 if (!appimage_type2_digest_md5(destination, digest_buffer)) {
 die("Failed to calculate MD5 digest");
 }
 FILE* destinationfp = fopen(destination, "r+");
 if (destinationfp == NULL) {
 die("Failed to open AppImage for updating");
 }
 if (fseek(destinationfp, digest_md5_offset, SEEK_SET) != 0) {
 fclose(destinationfp);
 die("Failed to embed MD5 digest: could not seek to section offset");
 }
 if (fwrite(digest_buffer, sizeof(char), section_size, destinationfp) != section_size) {
 fclose(destinationfp);
 die("Failed to embed MD5 digest: write failed");
 }
 fclose(destinationfp);
 }