dbg.c

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <linux/elf.h>
#include <sys/ptrace.h>
#include <linux/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/syscall.h>
#include <sys/user.h>
#include <errno.h>
#include <signal.h>

struct iovec {
    void *iov_base;
    unsigned int iov_len;
};

void err(char *str)
{
    fprintf(stderr, "ERROR: %s\n", str);
}

void target(char *argv[], char *argp[])
{
    if(ptrace(PTRACE_TRACEME, 0, NULL, NULL) != -1)
        execve(argv[0], argv, argp);
    else
        err("PTRACE_TRACEME");
    exit(0);
}

void controler(int pid)
{
    int status;
    struct user_regs_struct regs = {0};
    struct iovec iov;
    siginfo_t sif;
    int flag = 0;

    while (1) {
        iov.iov_len = sizeof(regs);
        iov.iov_base = &regs;
        memset(&regs, 0, sizeof(regs));
        waitpid(pid, &status, 0);
        if (WIFEXITED(status)) break;
        if (WIFSTOPPED(status)) {
            if (WSTOPSIG(status) != SIGTRAP) continue;
            int ret = ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov);
            printf("%d %d\n", ret, errno);
            printf("%llx: \n", regs.pc);
            ret = ptrace(PTRACE_GETSIGINFO, pid, NULL, &sif);
            printf("%d %d\n", ret, sif.si_signo);
            if (sif.si_signo == SIGTRAP && flag) {
                ret = ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &iov);
                printf("%d\n", ret);
                printf("%d\n", regs.a5);
                ptrace(PTRACE_KILL, pid, 0, NULL);
            }
            if (sif.si_signo == SIGTRAP && regs.pc == 0x10542) {
                regs.pc += 2;
                ret = ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &iov);
                printf("%d\n", ret);
                printf("%d\n", regs.a5);
                flag = 1;
            }
            ret = ptrace(PTRACE_SYSCALL, pid, 0, NULL);
        }
        ptrace(PTRACE_CONT, pid, 0, NULL);
    }
}

int exec_prog(char *argv[], char *argp[])
{
    int pid;

    switch(pid = fork())
        {
        case 0:
            target(argv, argp);
            break;
        case -1:
            err("FORK");
            break;
        default:
            controler(pid);
            break;
        }
    return 0;
}

int main(int argc, char *argv[], char *argp[])
{
    if(argc < 2){
        fprintf(stderr, "%s <args>\n", argv[0]);
        return 1;
    }

    argv++;
    exec_prog(argv, argp);
    return 0;
}

target.c

int main()
{
    __asm__ __volatile__ ("ebreak\n\t"
                          "addiw a5,a5,5\n\t"
                          "ebreak\n\t");
    return 0;
}