After reading a file, integers are set to arbitrarily large values - c

Question

I'm facing a very odd issue when trying to read a file in C.
I've parsed a file path via a command line argument, and gotten the size using the stat() function, and this works fine. However, after I read the file, all of my integers become arbitrarily large, and I cannot for the life of me figure out why!
Here is the relevant code from my main function:
int main( int argc, char *argv[] ) {
char *filepath = argv[1];
startaddress = strtol(argv[2], &endptra, 16);
endaddress = strtol(argv[3], &endptrb, 16);
int filesize = getfilesize(filepath);
printf("Filesize is %d\n", filesize);
unsigned char *mem = malloc( filesize );
printf("Filesize here is %d\n", filesize);
int size2 = filesize;
int test3 = 18;
printf("Size 2 set to %d\n", size2);
printf("Test 3 set to %d\n", test3);
// READ FILE
loadimage(filepath, &mem, filesize);
printf("Right after load image, file size is %d\n", filesize);
printf("%s\n", strerror(errno));
printf("Filesize is %d\n", filesize);
printf("size2: %d\n", size2);
printf("test3: %d\n", test3);
exit(0);
}
"getfilesize" is a relatively simple function that appears to work well:
int getfilesize(char *path) {
struct stat sbuffer;
int filesize = 0;
filesize = stat(path, &sbuffer);
if (filesize == -1) {
return 0;
} else {
return sbuffer.st_size;
}
}
Here is the loadimage function:
int loadimage(char *path, unsigned char *mem[], int size) {
int fdin, retval;
unsigned char buf[2048];
int nread;
printf("Path is: %s\n", path);
printf("Size is: %d\n", size);
fdin = open(path, O_RDONLY);
printf("fdin: %d\n", fdin);
if(fdin == -1) {
die(strerror( errno ));
}
int count = 0;
nread = read(fdin, buf, 2048);
for(; count < nread; count++) {
mem[count] = &buf[count];
}
if(nread == -1) {
die(strerror( errno ));
}
retval = close(fdin);
printf("Size is now %d\n", size);
return 1;
}
And this is the output of the result:
Filesize is 39
Filesize here is 39
Size 2 set to 39
Test 3 set to 18
Path is: test_file.txt
Size is: 39
fdin: 3
Size is now 39
Right after load image, file size is 32765
Success
Filesize is 32765
size2: 1418855892
test3: 32765
This is baffling to me and I cannot figure it out! It's confusing that even integers that I don't pass to the function are being modified as well. I'm assuming there's some sort of memory overflow happening somewhere, but I'm not used to working in the file system in C.
Thanks!

Answer 1

It seems to me that the problem is here:
int loadimage(char *path, unsigned char *mem[], int size) {
The mem argument should be just a pointer, or just an array, but not both. Aside from that, you're doing the same with the buf local variable, you're dereferencing it more than once when you use it (however that case might be harmless, I'm not sure). loadimage() should be:
int loadimage(char *path, unsigned char *mem, int size) {
int fdin, retval;
unsigned char buf[2048];
int nread;
printf("Path is: %s\n", path);
printf("Size is: %d\n", size);
fdin = open(path, O_RDONLY);
printf("fdin: %d\n", fdin);
if(fdin == -1) {
die(strerror( errno ));
}
int count = 0;
nread = read(fdin, buf, 2048);
for(; count < nread; count++) {
mem[count] = buf[count]; //no need for derefencing
}
if(nread == -1) {
die(strerror( errno ));
}
retval = close(fdin);
printf("Size is now %d\n", size);
return 1;
}
then, when calling it, do not dereference mem:
loadimage(filepath, mem, filesize);
Sorry, I don't have time so I haven't compiled it, but you get the idea, most probably that's the problem.