#define _GNU_SOURCE
#include <spawn.h>
#include <sched.h>
#include <unistd.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/wait.h>
#include "syscall.h"
#include "pthread_impl.h"
#include "fdop.h"
#include "libc.h"

struct args {
  int p[2];
  sigset_t oldmask;
  const char* path;
  int (*exec)(const char*, char* const*, char* const*);
  const posix_spawn_file_actions_t* fa;
  const posix_spawnattr_t* restrict attr;
  char *const *argv, *const *envp;
};

void __get_handler_set(sigset_t*);

static int __sys_dup2(int old, int new) {
#ifdef SYS_dup2
  return __syscall(SYS_dup2, old, new);
#else
  if (old == new) {
    int r = __syscall(SYS_fcntl, old, F_GETFD);
    return r < 0 ? r : old;
  } else {
    return __syscall(SYS_dup3, old, new, 0);
  }
#endif
}

static int child(void* args_vp) {
  int i, ret;
  struct sigaction sa = {0};
  struct args* args = args_vp;
  int p = args->p[1];
  const posix_spawn_file_actions_t* fa = args->fa;
  const posix_spawnattr_t* restrict attr = args->attr;
  sigset_t hset;

  close(args->p[0]);

  /* All signal dispositions must be either SIG_DFL or SIG_IGN
   * before signals are unblocked. Otherwise a signal handler
   * from the parent might get run in the child while sharing
   * memory, with unpredictable and dangerous results. To
   * reduce overhead, sigaction has tracked for us which signals
   * potentially have a signal handler. */
  __get_handler_set(&hset);
  for (i = 1; i < _NSIG; i++) {
    if ((attr->__flags & POSIX_SPAWN_SETSIGDEF) &&
        sigismember(&attr->__def, i)) {
      sa.sa_handler = SIG_DFL;
    } else if (sigismember(&hset, i)) {
      if (i - 32 < 3U) {
        sa.sa_handler = SIG_IGN;
      } else {
        __libc_sigaction(i, 0, &sa);
        if (sa.sa_handler == SIG_IGN)
          continue;
        sa.sa_handler = SIG_DFL;
      }
    } else {
      continue;
    }
    __libc_sigaction(i, &sa, 0);
  }

  if (attr->__flags & POSIX_SPAWN_SETPGROUP)
    if ((ret = __syscall(SYS_setpgid, 0, attr->__pgrp)))
      goto fail;

  /* Use syscalls directly because the library functions attempt
   * to do a multi-threaded synchronized id-change, which would
   * trash the parent's state. */
  if (attr->__flags & POSIX_SPAWN_RESETIDS)
    if ((ret = __syscall(SYS_setgid, __syscall(SYS_getgid))) ||
        (ret = __syscall(SYS_setuid, __syscall(SYS_getuid))))
      goto fail;

  if (fa && fa->__actions) {
    struct fdop* op;
    int fd;
    for (op = fa->__actions; op->next; op = op->next)
      ;
    for (; op; op = op->prev) {
      /* It's possible that a file operation would clobber
       * the pipe fd used for synchronizing with the
       * parent. To avoid that, we dup the pipe onto
       * an unoccupied fd. */
      if (op->fd == p) {
        ret = __syscall(SYS_dup, p);
        if (ret < 0)
          goto fail;
        __syscall(SYS_close, p);
        p = ret;
      }
      switch (op->cmd) {
        case FDOP_CLOSE:
          __syscall(SYS_close, op->fd);
          break;
        case FDOP_DUP2:
          if ((ret = __sys_dup2(op->srcfd, op->fd)) < 0)
            goto fail;
          break;
        case FDOP_OPEN:
          fd = __sys_open(op->path, op->oflag, op->mode);
          if ((ret = fd) < 0)
            goto fail;
          if (fd != op->fd) {
            if ((ret = __sys_dup2(fd, op->fd)) < 0)
              goto fail;
            __syscall(SYS_close, fd);
          }
          break;
      }
    }
  }

  /* Close-on-exec flag may have been lost if we moved the pipe
   * to a different fd. We don't use F_DUPFD_CLOEXEC above because
   * it would fail on older kernels and atomicity is not needed --
   * in this process there are no threads or signal handlers. */
  __syscall(SYS_fcntl, p, F_SETFD, FD_CLOEXEC);

  pthread_sigmask(
      SIG_SETMASK,
      (attr->__flags & POSIX_SPAWN_SETSIGMASK) ? &attr->__mask : &args->oldmask,
      0);

  args->exec(args->path, args->argv, args->envp);
  ret = -errno;

fail:
  /* Since sizeof errno < PIPE_BUF, the write is atomic. */
  ret = -ret;
  if (ret)
    while (__syscall(SYS_write, p, &ret, sizeof ret) < 0)
      ;
  _exit(127);
}

int __posix_spawnx(pid_t* restrict res,
                   const char* restrict path,
                   int (*exec)(const char*, char* const*, char* const*),
                   const posix_spawn_file_actions_t* fa,
                   const posix_spawnattr_t* restrict attr,
                   char* const argv[restrict],
                   char* const envp[restrict]) {
  pid_t pid;
  char stack[1024];
  int ec = 0, cs;
  struct args args;

  if (pipe2(args.p, O_CLOEXEC))
    return errno;

  pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);

  args.path = path;
  args.exec = exec;
  args.fa = fa;
  args.attr = attr ? attr : &(const posix_spawnattr_t){0};
  args.argv = argv;
  args.envp = envp;
  pthread_sigmask(SIG_BLOCK, SIGALL_SET, &args.oldmask);

  pid = __clone(child, stack + sizeof stack, CLONE_VM | CLONE_VFORK | SIGCHLD,
                &args);
  close(args.p[1]);

  if (pid > 0) {
    if (read(args.p[0], &ec, sizeof ec) != sizeof ec)
      ec = 0;
    else
      waitpid(pid, &(int){0}, 0);
  } else {
    ec = -pid;
  }

  close(args.p[0]);

  if (!ec && res)
    *res = pid;

  pthread_sigmask(SIG_SETMASK, &args.oldmask, 0);
  pthread_setcancelstate(cs, 0);

  return ec;
}

int posix_spawn(pid_t* restrict res,
                const char* restrict path,
                const posix_spawn_file_actions_t* fa,
                const posix_spawnattr_t* restrict attr,
                char* const argv[restrict],
                char* const envp[restrict]) {
  return __posix_spawnx(res, path, execve, fa, attr, argv, envp);
}