/*
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2026 Alex S <iwtcex@gmail.com>
 */

#include <machine/reg.h>
#include <sys/ptrace.h>
#include <sys/syscall.h>
#include <sys/wait.h>

#include <assert.h>
#include <err.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#ifndef __amd64__
#error "amd64 only"
#endif

/*
 * This test substitutes exit(42) instead of getpid() using ptrace.
 */

static const int EXPECTED_EXIT_CODE = 42;

static void
tamper(pid_t pid)
{
        struct ptrace_lwpinfo info;
        struct reg regs;

        if (ptrace(PT_LWPINFO, pid, (caddr_t)&info, sizeof(info)) == -1)
                err(1, "ptrace(PT_LWPINFO)");

        if ((info.pl_flags & PL_FLAG_SCE) != 0 &&
            info.pl_syscall_code == SYS_getpid) {
                if (ptrace(PT_GETREGS, pid, (caddr_t)&regs, sizeof(regs)) == -1)
                        err(1, "ptrace(PT_GETREGS)");

                regs.r_rax = SYS_exit;
                regs.r_rdi = EXPECTED_EXIT_CODE;

                if (ptrace(PT_SETREGS, pid, (caddr_t)&regs, sizeof(regs)) == -1)
                        err(1, "ptrace(PT_SETREGS)");
        }
}

int
main(void)
{
        pid_t pid;
        int status;

        pid = fork();
        if (pid == -1)
                err(1, "fork");

        if (pid == 0) {
                raise(SIGSTOP);
                (void)getpid();
                exit(0);
        } else {
                if (ptrace(PT_ATTACH, pid, 0, 0) == -1)
                        err(1, "ptrace(PT_ATTACH)");

                for (;;) {
                        if (wait(&status) == -1)
                                err(1, "wait");

                        if (WIFEXITED(status)) {
                                if (WEXITSTATUS(status) == EXPECTED_EXIT_CODE) {
                                        printf("exit code changed\n");
                                        exit(0);
                                } else {
                                        printf("unable to change exit code\n");
                                        exit(1);
                                }
                        }

                        assert(WIFSTOPPED(status));
                        tamper(pid);

                        if (ptrace(PT_TO_SCE, pid, (caddr_t)1, 0) == -1)
                                err(1, "ptrace(PT_TO_SCE)");
                }
        }
}