I want to extend the u-boot SPL code with some fuzzy extractor logic by adding code into `{u-boot_sources}/arch/arm/cpu/armv7/omap-common/hwinit-common.c`. U-boot shall be used on a PandaBoard ES (omap4460 SoC).
Thus, first I successfully implemented the code on my x86 pc and I am porting it to the ARM-based PandaBoard. The complete code can be found here (as a side note the "main" function is s_init()):
However, I am expecting dozens of unexptected effects, which results in either stopping during the execution of the code, stopping u-boot after reading u-boot.img or not sending output (and thus not booting) at all.
For example, I want to call two functions (`computeSyndrome`, `decodeErrors`) inside a `for`-loop, which is part of another function `golayDecode`.
For my first problem please ignore the code below the multiline comment starting with `/* >>>> These lines of code below totally break u-boot`. Also only the function `computeSyndrome` in conjunction with the calling function `golayDecode` is important.
The issue: If comment out both functions `computeSyndrome` and `decodeErrors` everything works fine and the OS (Android) is booting. However, if `computeSyndrome` is not commented out and thus gets processed, u-boot stucks after displaying `reading u-boot.img`.
The funny thing about it: even if I replace `computeSyndrome` with a bogus function which does not but iterating a values or displaying stuff, u-boot stucks as well.
Furthermore, if I remove the multiline comment furhter below to also include the residual code, u-boot doesn't display ony character. (1*)
I am a beginner regarding microprocessor programming but I can not figure out a possible error in these 12 lines of the computeSyndrome function or the general behaviour of u-boot at all. (2*)
Does anyone have a clue what I am missing?
Thanks,
P.
1* I am using minicom to display the output of u-boot, which I receive over serial-usb-converter.
2* I am using the following compiler flags to make sure there are no errors at compile time: `-Wall -Wstrict-prototypes -Wdisabled-optimization -W -pedantic`
void golayDecode(volatile int x[12], volatile int y[12], volatile unsigned int golayEncodedSecret[30], volatile unsigned int s, volatile unsigned char repetitionDecodedSecretBits[360]){
printf("\n[I] - Performing Golay decoding\r\n");
volatile unsigned char secret[22] = {0};
volatile unsigned char currentByte = 0, tmpByte = 0;
volatile unsigned int golayDecodedSecret[30] ={0};
volatile int twelveBitCounter = 0;//, j = 0, k = 0, q = 0, aux = 0, found = 0, bitCounter = 0, i_2 = 7, currentSecretEncByte = 0x00;
volatile int c_hat[2] = {0}, e[2] = {0};
e[0] = s;
e[1] = 0;
for(twelveBitCounter = 0; twelveBitCounter < 30; twelveBitCounter+=2){
printf("Computing syndrome and decoding errors for bytes %03x & %03x\n", golayEncodedSecret[twelveBitCounter], golayEncodedSecret[twelveBitCounter+1]);
computeSyndrome(golayEncodedSecret[twelveBitCounter], golayEncodedSecret[twelveBitCounter+1], x, y, s);
decodeErrors(golayEncodedSecret[i], golayEncodedSecret[i+1], x, y, s);
}
printf("\n[D] - Reconstructing secret bytes\r\n");
/* >>>> These lines of code below totally break u-boot
for(i = 0; i < 30; i+=2){
currentSecretEncByte = golayDecodedSecret[i];
volatile int j = 11;
// Access each source bit
for(; 0<=j; j--){
volatile int currentSourceBit = (currentSecretEncByte >> j) & 0x01;
repetitionDecodedSecretBits[bitCounter] = currentSourceBit;
bitCounter++;
}
}
k = 0;
for(i = 0; i<176; i++){
tmpByte = repetitionDecodedSecretBits[i] << i_2;
currentByte = currentByte | tmpByte;
i_2--;
if(i_2==0){ // We collected 8 bits and created a byte
secret[k] = currentByte;
i_2 = 7;
tmpByte = 0x00;
currentByte = 0x00;
k++;
}
}
SHA256_CTX ctx;
unsigned char hash[32];
printf("\n[I] - Generating secret key K\n");
sha256_init(&ctx);
sha256_update(&ctx,secret,strlen((const char*)secret));
sha256_final(&ctx,hash);
printf("\n[I] - This is our secret key K\n\t==================================\n\t");
print_hash(hash);
printf("\t==================================\n");
*/
}
/* Function for syndrome computation */
void computeSyndrome(int r0, int r1, volatile int x[12], volatile int y[12], volatile unsigned int s){
unsigned int syndromeBitCounter, syndromeMatrixCounter, syndromeAux;
s = 0;
for(syndromeMatrixCounter=0; syndromeMatrixCounter<12; syndromeMatrixCounter++){
syndromeAux = 0;
for(syndromeBitCounter=0; syndromeBitCounter<12; syndromeBitCounter++){
syndromeAux = syndromeAux^((x[syndromeMatrixCounter]&r0)>>syndromeBitCounter &0x01);
}
for(syndromeBitCounter=0; syndromeBitCounter<12; syndromeBitCounter++){
syndromeAux = syndromeAux^((y[syndromeMatrixCounter]&r1)>>syndromeBitCounter &0x01);
}
s = (s<<1)^syndromeAux;
}
}
/* Funcion to recover original byte */
void decodeErrors(int r0, int r1, volatile int x[12], volatile int y[12], volatile unsigned int s){
//printf("\n[D] - Starting to decode errors for %3x | %3x\n", r0, r1);
volatile unsigned int c_hat[2] = {0xaa}, e[2] = {0xaa};
volatile unsigned int q;
unsigned int i, j, aux, found;
//printf("Step 2\n");
if(weight(s)<=3){
e[0] = s;
e[1] = 0;
}else{
/******* STEP 3 */
//printf("Step 3\n");
i = 0;
found = 0;
do{
if (weight(s^y[i]) <=2){
e[0] = s^y[i];
e[1] = x[i];
found = 1;
printf("\ntest 2\n");
}
i++;
}while ((i<12) && (!found));
if (( i==12 ) && (!found)){
/******* STEP 4 */
//printf("Step 4\n");
q = 0;
for (j=0; j<12; j++){
aux = 0;
for (i=0; i<12; i++)
aux = aux ^ ( (y[j]&s)>>i & 0x01 );
q = (q<<1) ^ aux;
}
/******* STEP 5 */
//printf("Step 5\n");
if (weight(q) <=3){
e[0] = 0;
e[1] = q;
}else{
/******* STEP 6 */
//printf("Step 6\n");
i = 0;
found = 0;
do{
if (weight(q^y[i]) <=2){
e[0] = x[i];
e[1] = q^y[i];
found = 1;
}
i++;
}while((i<12) && (!found));
if ((i==12) && (!found)){
/******* STEP 7 */
printf("\n[E] - uncorrectable error pattern! (%3x | %3x)\n", r0, r1);
/* You can raise a flag here, or output the vector as is */
//exit(1);
}
}
}
}
c_hat[0] = r0^e[0];
c_hat[1] = r1^e[1];
//printf("\t\tEstimated codeword = %x%x\n", c_hat[0], c_hat[1]);
}
