Invoke Cygwin programs for msys2-cygwin

msys_mingw_cygexec.c

/* SPDX-License-Identifier: MIT */

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define  WIN32_LEAN_AND_MEAN
#include <windows.h>

#define AUTOCLO           __attribute__((cleanup(__drop_fd)))
#define AUTOFREE          __attribute__((cleanup(__drop_mem)))

#define err(_fmt, ...)    fprintf (stderr, "%s: " _fmt "\n", progname, ##__VA_ARGS__)
#define die(_fmt, ...)        \
{                             \
  err(_fmt, ##__VA_ARGS__);   \
  exit (1);                   \
}

static const char *progname;

static void
__drop_fd (int *fd)
{
  if (*fd < 0)
    return;

  close (*fd);
}

static void
__drop_mem (void *ptr)
{
#define _ptr   (*(void **)ptr)

  if (!_ptr)
    return;

  free (_ptr);
}

static inline const char *
_map2tgt (unsigned short nt_mach)
{
  switch (nt_mach)
  {
    case IMAGE_FILE_MACHINE_AMD64:
      return "x86_64-pc-cygwin";
    default:
      return NULL;
  }
}

__attribute__((noreturn)) static inline void
_cygexec (const char *prog,
          const char *tgt,
          const char *const *argv)
{
  AUTOFREE char *pfx = NULL;
  AUTOFREE char *old_path = NULL;
  AUTOFREE char *buff = NULL;
  ssize_t len;
  int ex;

#define _agetenv(name)   strdup (getenv (name))

  // e.g. /mingw64
  pfx = _agetenv("MINGW_PREFIX");
  if (!pfx)
    die("Not running in an MSYS2 MINGW terminal");

  old_path = _agetenv("PATH");
  if (!old_path)
    die("PATH is not set");

  // make target DLLs available in PATH

#define _format_new_path(_buff, _len) \
  snprintf (_buff, _len, "PATH=%s/%s/bin;%s", pfx, tgt, old_path)

  len = _format_new_path(NULL, 0);
  if (len < 0)
print_err:
    die("%s", strerror (errno));

  len += 1;  // terminate byte

  buff = malloc (len);
  if (!buff)
    goto print_err;

  if (_format_new_path(buff, len) < 0)
    goto print_err;

  if (putenv (buff))
    goto print_err;

  // avoid freeing its now a part of environ
  buff = NULL;

  ex = _spawnv (P_WAIT, prog, argv);
  if (ex < 0)
    goto print_err;

  exit (ex);
}

int
main (int argc, char **argv)
{
  AUTOCLO int fd = -1;
  union
  {
    IMAGE_DOS_HEADER dos;
    IMAGE_NT_HEADERS nt;
  } hdr;
  union
  {
    ssize_t cnt;
    off_t off;
  } err;
  const char *tgt;

  progname = argv[0];

  if (argc < 2)
  {
    fprintf (stderr, "Usage: %s PROGRAM [ARGUMENTS...]\t"
                     "Run the specified program\n", progname);

    return 1;
  }

  // check dos header

#define _prog    argv[1]

  fd = open (_prog, O_RDONLY | O_BINARY);
  if (fd < 0)
  {
print_err:
    err("%s: %s", _prog, strerror (errno));

    return 1;
  }

  err.cnt = read (fd, &hdr.dos, sizeof(hdr.dos));
  if (err.cnt < 0)
    goto print_err;
  else if (err.cnt != sizeof(hdr.dos))
  {
too_small:
    err("%s: File too small to be an valid executable", _prog);

    return 1;
  }

  if (hdr.dos.e_magic != IMAGE_DOS_SIGNATURE)
  {
bad_prog:
    err("%s: Is not a Cygwin program", _prog);

    return 1;
  }

  // check nt header

#define _nt_hdr_off    (hdr.dos.e_lfanew)
  err.off = lseek (fd, _nt_hdr_off, SEEK_SET);
  if (err.off < 0)
    goto print_err;
  else if (err.off != _nt_hdr_off)
    goto too_small;

  err.cnt = read (fd, &hdr.nt, sizeof(hdr.nt));
  if (err.cnt < 0)
    goto print_err;
  else if (err.cnt != sizeof(hdr.nt))
    goto too_small;

  if (hdr.nt.Signature != IMAGE_NT_SIGNATURE)
    goto bad_prog;

  tgt = _map2tgt (hdr.nt.FileHeader.Machine);
  if (!tgt)
  {
    err("%s: Unknown architecture", _prog);

    return 1;
  }

  _cygexec (_prog, tgt, (const char *const *)&argv[1]);
}