Chapter 13: System Calls
if (val == -1) {
return -1;
}*res = val;
return 0;
}
void trace_syscall() {
long res;
res = ptrace(PTRACE_SYSCALL, pid, (char*) 1, 0);
if (res < 0) {
printf("Failed to execute until next syscall: %d\n", res);
}
}
void sigchld_handler (int signum) {
long scno;
int res;
/* Find out the system call (system-dependent)...*/
if (upeek(pid, 4*ORIG_EAX, &scno) < 0) {
return;
}/* ... and output the information */
if (scno != 0) {
printf("System call: %u\n", scno);
}/ Activate tracing until the next system call /
trace_syscall();
}
int main(int argc, char** argv) {
int res;
/* Check the number of arguments */
if (argc != 2) {
printf("Usage: ptrace <pid>\n");
exit(-1);
}/* Read the desired pid from the command-line parameters */
pid = strtol(argv[1], NULL, 10);
if (pid <= 0) {
printf("No valid pid specified\n");
exit(-1);
} else {
printf("Tracing requested for PID %u\n", pid);
}/* Install handler for SIGCHLD */