/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2021 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "ape/ape.h"
#include "libc/atomic.h"
#include "libc/calls/blockcancel.internal.h"
#include "libc/calls/blocksigs.internal.h"
#include "libc/calls/calls.h"
#include "libc/calls/cp.internal.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/cosmo.h"
#include "libc/dce.h"
#include "libc/errno.h"
#include "libc/fmt/magnumstrs.internal.h"
#include "libc/intrin/bits.h"
#include "libc/intrin/describeflags.internal.h"
#include "libc/intrin/safemacros.internal.h"
#include "libc/intrin/strace.internal.h"
#include "libc/limits.h"
#include "libc/mem/alloca.h"
#include "libc/paths.h"
#include "libc/proc/execve.internal.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/stack.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/at.h"
#include "libc/sysv/consts/o.h"
#include "libc/sysv/consts/ok.h"
#include "libc/sysv/errfuns.h"

#define ELIBBAD_LINUX 80
#define EBADEXEC_XNU  85
#define EBADARCH_XNU  86

static struct {
  atomic_uint once;
  const char *home;
  const char *tmpdir;
} g_execve;

static bool IsApeFile(const char *path) {
  if (endswith(path, ".com")) {
    return true;
  } else {
    bool res = false;
    BLOCK_SIGNALS;
    int fd;
    char buf[8];
    int flags = O_RDONLY | O_NOCTTY | O_NONBLOCK | O_CLOEXEC;
    if ((fd = sys_openat(AT_FDCWD, path, flags, 0)) != -1) {
      res = sys_pread(fd, buf, 8, 0, 0) == 8 && IsApeLoadable(buf);
      sys_close(fd);
    }
    ALLOW_SIGNALS;
    return res;
  }
}

static const char *Join(const char *a, const char *b, char buf[PATH_MAX]) {
  size_t n, m;
  if (a && *a) {
    n = strlen(a);
    m = strlen(b);
    if (n + m + 1 < PATH_MAX) {
      stpcpy(stpcpy(buf, a), b);
      return buf;
    }
  }
  return 0;
}

static void RetryExecve(const char *prog, char **argv, char *const *envp) {
  if ((argv[0] = (char *)prog)) {
    STRACE("execve(%#s, %s) due to %s", prog, DescribeStringList(argv),
           _strerrno(errno));
    __sys_execve(prog, argv, envp);
  }
}

static void SetupExecve(void) {
  g_execve.home = getenv("HOME");
  g_execve.tmpdir = getenv("TMPDIR");
}

__attribute__((__constructor__)) static void InitExecve(void) {
  cosmo_once(&g_execve.once, SetupExecve);
}

int sys_execve(const char *prog, char *const argv[], char *const envp[]) {

  // try kernel
  // this also checks execute bit
  __sys_execve(prog, argv, envp);
  if (!(errno == ENOEXEC || (IsLinux() && errno == ELIBBAD_LINUX))) {
    return -1;
  }

  // allocate memory
  int argc;
  for (argc = 0; argv[argc];) ++argc;
#pragma GCC push_options
#pragma GCC diagnostic ignored "-Walloca-larger-than="
  int nbytes = (argc + 4) * sizeof(char *);
  int ntotal = nbytes + PATH_MAX;
  if (__get_safe_size(ntotal, 4096) < ntotal) return enomem();
  char **shargs = alloca(nbytes);
  CheckLargeStackAllocation(shargs, nbytes);
#pragma GCC pop_options

  // try ape loader
  if (IsApeFile(prog)) {
    shargs[1] = (char *)"-";
    shargs[2] = (char *)prog;
    memcpy(shargs + 3, argv, (argc + 1) * sizeof(char *));
    RetryExecve("/usr/bin/ape", shargs, envp);
    char *buf = alloca(PATH_MAX);
    const char *name = "/.ape-" APE_VERSION_STR;
    InitExecve();
    RetryExecve(Join(g_execve.tmpdir, name, buf), shargs, envp);
    RetryExecve(Join(g_execve.home, name, buf), shargs, envp);
    RetryExecve(Join(".", name, buf), shargs, envp);
  }

  // try bourne shell
  shargs[0] = _PATH_BSHELL;
  shargs[1] = (char *)prog;
  memcpy(shargs + 2, argv + 1, argc * sizeof(char *));
  RetryExecve(shargs[0], shargs, envp);

  enoexec();
  return -1;
}