SegFault in Cache Sim C program - c

Question

EDIT: so it's easier for you guys to find where in my code I think the segfault is happening, look under the commented section called /* Cache Structure */
EDIT2: made a huge mistake with gdb the correct output when it segfaults from gdb is:
(gdb) run
Starting program: /.autofs/ilab/ilab_users/petejodo/Assignment4/a.out
1
/.autofs/ilab/ilab_users/petejodo/Assignment4/a.out
Program received signal SIGSEGV, Segmentation fault.
0x00449453 in strlen () from /lib/libc.so.6
(gdb)
EDIT3: after resorting to n00b tactics like printing lines, I've found it prints before:
file = fopen(purefile, "r");
if (file == 0){
printf ("Could not find file!\n");
return 0;
}
but doesnt print "test" I have underneath it.
ORIGINAL
So after checking all the threads on segfault and using gdb I can't figure out why my program is segfaulting at this line. I'm writing a cache simulator (only have write-through in my code currently) and I didn't include my methods because they are fine, it's in the main method.
int main(int argc, char **argv) {
FILE* file;
/* Counter variables */
int i;
int j;
/* Helper Variables */
int setAdd;
int totalSet;
int trash;
int size;
int extra;
char rw;
/* Necessary Character Arrays */
char hex[100];
char bin[100];
char origTag[100];
char bbits[100];
char sbits[100];
char tbits[100];
/* Cache Info Variables */
int setNumber = 4096; /* cacheSize/blockSize : (16,384/4) */
int setBits = 12; /* log(setNumber)/log(2) : (log(4096)/log(2)) */
int tagSize = 18; /* 32-(blockBits + setBits) **blockBits = log(blockSize)/log(2)** : (32 - (2 + 12) */
/* Results */
int cacheHit = 0;
int cacheMiss = 0;
int write = 0;
int read = 0;
/* Cache Structure */
tempLine cache[4096];
char* style;
char* purefile;
if (strcmp(argv[1], "-h")==0)
{
puts("Usage: sim <write policy> <trace file>");
return 0;
}
style = argv[1];
purefile = argv[2];
file = fopen(purefile, "r");/* HYPOTHESIZED SEGFAULT HERE */
if (file == 0){
printf ("Could not find file!\n");
return 0;
}
printf("test1");
/* Setting Structure Default Values */
for(i = 0; i < setNumber; i++)
{
cache[i].tag = (char *)malloc(sizeof(char)*(tagSize + 1));
for(j = 0; j < tagSize; j++)
{
cache[i].tag[j] = '0';
}
cache[i].valid = 0;
}
/* Main Loop */
while(fgetc(file) != '#')
{
setAdd = 0;
totalSet = 0;
fseek(file, -1, SEEK_CUR);
fscanf(file, "%d: %c %s\n", &trash, &rw, origTag);
/* Cutting off '0x' off from address '0x00000000' and adding 0's if necessary */
size = strlen(origTag);
extra = (10 - size);
for(i = 0; i < extra; i++)
hex[i] = '0';
for(i = extra, j = 0; i < (size-(2-extra)); i++, j++)
hex[i] = origTag[j + 2];
hex[8] = '\0';
hex2bin(hex, bin);
split(bin, bbits, sbits, tbits);
/* Changing cArray into int */
for(i = 0, j = (setBits - 1); i < setBits; i++, j--)
{
if (sbits[i] == '1')
setAdd = 1;
if (sbits[i] == '0')
setAdd = 0;
setAdd = setAdd * pow(2, j);
totalSet += setAdd;
}
/* Calculating Hits and Misses */
if (cache[totalSet].valid == 0)
{
cache[totalSet].valid = 1;
strcpy(cache[totalSet].tag, tbits);
}
if ((cache[totalSet].valid == 1) && (strcmp(cache[totalSet].tag, tbits) == 0))
{
/* HIT */
if (rw == 'W')
{
cacheHit++;
write++;
}
if (rw == 'R')
cacheHit++;
}
else
{
/* MISS */
if (rw == 'R')
{
cacheMiss++;
read++;
}
if (rw == 'W')
{
cacheMiss++;
read++;
write++;
}
cache[totalSet].valid = 1;
strcpy(cache[totalSet].tag, tbits);
}
/* End Calculations */
}
printResult(cacheHit, cacheMiss, read, write);
return 0;
}
And what I got out of gdb was this:
**INCORRECT**
(gdb) run
Starting program: /.autofs/ilab/ilab_users/petejodo/Assignment4/a.out
Program received signal SIGSEGV, Segmentation fault.
0x080489b6 in main (argc=1, argv=0xbfffe954) at sim.c:128
128 if (strcmp(argv[1], "-h")==0)
(gdb) bt
#0 0x080489b6 in main (argc=1, argv=0xbfffe954) at sim.c:128
I'm kind of lost, any help would be great. Thanks!
Oh, and also checking the value of argv[1] it is NULL or 0x0 because I think it is because of that. argv[1] is supposed to contain either the help flag or write through or write back, I just haven't coded in whether to check for write through or write back just yet.

Answer 1

You need to test if argc > 1 if you want to access argv[1]. A program always receives the name it was called by (e.g. ./a.out in your case) as argv[0], so argc >= 1 is always true. To access the first real argument - i.e. the second element of argv - you need to test if there are at least two arguments. However, testing if there are > n elements when accessing argv[n] is more readable IMO since both numbers are the same.
Here's an example on how to change your code:
if (argc < 3 || (argv > 1 && strcmp(argv[1], "-h")==0))
{
puts("Usage: sim <write policy> <trace file>");
return 0;
}
In this case you will show an error if there are not enough arguments provided to have valid argv[1] and argv[2] elements or if the first argument is -h (in case someone puts stuff after -h - otherwise it'd be handled by the too-few-arguments check).
You should have a look at getopt() by the way - it makes argument/switch parsing much easier and cleaner.