debugger.c

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

/*
Need entitlements added to binary

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>com.apple.security.cs.debugger</key>
    <true/>
</dict>
</plist>

*/

static void setup_inferior(const char *path, char *const argv[])
{
    int result;
    ptrace(PT_TRACE_ME, 0, 0, 0);
    execv(path, argv);
}

static void attach_to_inferior(pid_t pid)
{
    while(1) {
        int	status;
        waitpid(pid, &status, 0);

        if (WIFSTOPPED(status) && WSTOPSIG(status) == SIGTRAP) {
            printf("Inferior stopped on SIGTRAP - continuing...\n");

            task_t task;
            kern_return_t kr;

            kr = task_for_pid(mach_task_self(), pid, &task);
            if (kr != KERN_SUCCESS) {
                mach_error("task_for_pid:", kr);
            } 
            else {
                printf("Got task port\n");
            }

            ptrace(PT_CONTINUE, pid, (caddr_t)1, 0);
        }
        else if (WIFEXITED(status)) {
            printf("Inferior exited - debugger terminating...\n");
            exit(0);
        }
    }
}

void dbg_inferior_exec(const char *path, char *const argv[])
{
    pid_t result;

    do {
        result = fork();
        switch (result) {
        case 0:   // inferior
            setup_inferior(path, argv);
            break;
        case -1:  // error
            break;
        default:  // debugger
            attach_to_inferior(result);
            break;
        }
  } while (result == -1 && errno == EAGAIN);
}

int main()
{
    char *argv[1] = { 0 };
    dbg_inferior_exec("./hello", argv);

    return 0;
}