basic usage of ptrace(2)

gistfile1.txt

$ gcc itrace.c -o itrace

$ ./itrace /bin/ls | head
7f86ae81d2d0
7f86ae81d2d3
7f86ae820a70
7f86ae820a71
7f86ae820a74
7f86ae820a76
7f86ae820a78
7f86ae820a7a
7f86ae820a7c
7f86ae820a7d

itrace.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ptrace.h>
#include <sys/user.h>
#include <sys/types.h>
#include <sys/wait.h>

int main(int argc, char *argv[])
{
    pid_t pid;
    int status;
    struct user_regs_struct regs;

    if (argc < 2) {
        fprintf(stderr, "Usage: %s PROG [ARGS]\n", argv[0]);
        exit(1);
    }

    pid = fork();
    if (pid == -1) {
        fprintf(stderr, "fork failed\n");
        exit(1);
    } else if (pid == 0) {
        ptrace(PTRACE_TRACEME, 0, NULL, NULL);
        execvp(argv[1], argv+1);
        perror(argv[0]);
        exit(1);
    } else {
        while (1) {
            waitpid(pid, &status, 0);
            if (WIFEXITED(status) || WIFSIGNALED(status)) {
                break;
            }

            ptrace(PTRACE_GETREGS, pid, NULL, &regs);

            printf("%llx\n", regs.rip);

            ptrace(PTRACE_SINGLESTEP, pid, NULL, NULL);
        }
    }

    return 0;
}