script for running assembley code

[tony2007]

Hi everyone ;)

It is my first post, and I am quite Newbie in C. Here is my prob:

I am running Linux Ubuntu Dapper 6.06 and I am trying to run a script for printing and executing .asm code (shellcode) which is the following:

/*
* Generic program for testing shellcode byte arrays.
* Created by zillion and EVL
*
* Safemode.org !! Safemode.org !!
*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>

/*
* Print message
*/
static void
croak(const char *msg) {
fprintf(stderr, "%s\n", msg);
fflush(stderr);
}
/*
* Educate user.
*/
static void
usage(const char *prgnam) {
fprintf(stderr, "\nExecute code : %s -e <file-containing-shellcode>\n", prgnam);
fprintf(stderr, "Convert code : %s -p <file-containing-shellcode> \n\n", prgnam);
fflush(stderr);
exit(1);
}
/*
* Signal error and bail out.
*/
static void
barf(const char *msg) {
perror(msg);
exit(1);
}

/*
* Main code starts here
*/

int
main(int argc, char **argv) {
FILE *fp;
void *code;
int arg;
int i;
int l;
int m = 15; /* max # of bytes to print on one line */

struct stat sbuf;
long flen; /* Note: assume files are < 2**32 bytes long ;-) */
void (*fptr)(void);

if(argc < 3) usage(argv[0]);
if(stat(argv[2], &sbuf)) barf("failed to stat file");
flen = (long) sbuf.st_size;
if(!(code = malloc(flen))) barf("failed to grab required memeory");
if(!(fp = fopen(argv[2], "rb"))) barf("failed to open file");
if(fread(code, 1, flen, fp) != flen) barf("failed to slurp file");
if(fclose(fp)) barf("failed to close file");

while ((arg = getopt (argc, argv, "e:p:")) != -1){
switch (arg){
case 'e':
croak("Calling code ...");
fptr = (void (*)(void)) code;
(*fptr)();
break;
case 'p':
printf("\n\nchar shellcode[] =\n");
l = m;
for(i = 0; i < flen; ++i) {
if(l >= m) {
if(i) printf("\"\n");
printf( "\t\"");
l = 0;
}
++l;
printf("\\x%02x", ((unsigned char *)code)[i]);
}
printf("\";\n\n\n");

break;
default :
usage(argv[0]);
}
}


return 0;
}

-----------------------------------------------------------------------------------------

The code part of the script is, as I said, some compiled assembley code.
When I use the ./s-proc -p asmfile..... It prints the shellcode with no problem but when I try the ./s-proc -e asmfile It gives me always segmentation fault. I try to use the gdb to debugg and I think the program crashes in the (*fptr)(); line of the case 'e' block.
I don't have a lot of experience with pointers but I would like to understand what is happening if someone is kind to explain.
I'm sorry for possible errors in this post.
Thanks in advance
tony2007