Problem - Kevin Tafuro

for (j = 8; j > 0; j--) {
if (crc & 1) crc = (crc >> 1) ^ CRC_POLY;
else crc >>= 1;
}
crc32_table[i] = crc;
}
return 1;
}
unsigned long crc32_calc(unsigned char *buf, int buf_len) {
int x;
unsigned long crc = 0xFFFFFFFF;
if (!crc32_table[0]) crc32_table_init( );
for (x = 0; x < buf_len; x++) crc = crc32(crc, buf[x]);
return crc;
}
The following program demonstrates the use of the checksum implementation. Note
that the program is first compiled with a printf( ) in main( ) that will print the
checksum to stdout. As long as main( ) is linked into the program after the buffer
being checked, this printf( ) can be removed and the program recompiled without
the value of the checksum changing. Once the checksum is known, a hex editor can
be used to patch the checksum value into the location crc32_stored. In this example,
the four bytes of the checksum are stored between two 0xFEEDFACE markers that
should be overwritten with random bytes before the binary is distributed. Note that
the markers will be stored in little-endian order in the binary, hence the reversed
ordering of the bytes in the C source.
#include
/* warning: replace "crc32_stored" with the real checksum! */
asm(".long 0xCEFAEDFE \n" /* look for 0xFEEDFACE markers */
"crc32_stored: \n"
".long 0xFFFFFFFF \n" /* change this in the binary! */
".long 0xCEFAEDFE \n" /* end marker */
);
CRC_START_BLOCK(test)
int test_routine(int a) {
while (a < 12) a = (a - (a * 3)) + 1;
return a;
}
CRC_END_BLOCK( test )
int main(int argc, char *argv[ ]) {
unsigned long crc;
crc = crc32_calc(CRC_BLOCK_ADDR(test), CRC_BLOCK_LEN(test));
#ifdef TEST_BUILD
/* This printf( ) displays the CRC value that needs to be stored in the program.
* The printf( ) must be removed, and the program recompiled before distribution.
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