open-process and related functions for MinGW Guile

[Eli Zaretskii <eliz@gnu.org>]

This is a sequel to the thread that started here:

  http://lists.gnu.org/archive/html/guile-devel/2014-02/msg00047.html

As agreed with Mark at the end of that thread, please find below
patches that enable open-process and friends in the MinGW build of
Guile.  The main changes since the patches I presented in February
are:

 . Guile's standard handles are not redirected before running the
   child process.

 . The code which runs the child process supports both a Unixy shell
   (if available), which is useful for the test suite, the stock
   Windows shell cmd.exe, and other programs.  This support includes
   correct handling of quoted command-line arguments.

 . Translation of signals to exit status and back is based on a
   mapping that produces signal values identical to the ones in
   signal.h, as opposed to some convention private to Guile.

 . waitpid emulation supports WNOHANG (required to pass the
   rnrs-libraries test).

I put most of the Windows-specific code on a separate file, I hope
that is OK.

Building the patched Guile and running the relevant tests in
ports.test and popen.test revealed some additional issues, some
related, some not entirely related.  I will address them in a separate
message.

Thanks.

--- libguile/posix.c~	2014-06-22 19:08:35.862625000 +0300
+++ libguile/posix.c	2014-06-29 18:36:02.000000000 +0300
@@ -84,6 +84,32 @@
 #if HAVE_SYS_WAIT_H
 # include <sys/wait.h>
 #endif
+#ifdef __MINGW32__
+
+#include <c-strcase.h>
+
+# define WEXITSTATUS(stat_val) ((stat_val) & 255)
+# define WIFEXITED(stat_val)   (((stat_val) & 0xC0000000) == 0)
+# define WIFSIGNALED(stat_val) (((stat_val) & 0xC0000000) == 0xC0000000)
+# define WTERMSIG(stat_val)    win32_status_to_termsig (stat_val)
+/* The funny conditional avoids a compiler warning in status:stop_sig.  */
+# define WIFSTOPPED(stat_val)  ((stat_val) == (stat_val) ? 0 : 0)
+# define WSTOPSIG(stat_var)    (0)
+# include <process.h>
+# define HAVE_WAITPID 1
+  static int win32_status_to_termsig (DWORD);
+  static int win32_signal_to_status (int);
+# define getuid()              (500) /* Local Administrator */
+# define getgid()              (513) /* None */
+# define setuid(u)             (0)
+# define setgid(g)             (0)
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+# define WNOHANG               1
+  int waitpid (intptr_t, int *, int);
+# include "win32-proc.c"
+#endif	/* __MINGW32__ */
+
 #ifndef WEXITSTATUS
 # define WEXITSTATUS(stat_val) ((unsigned)(stat_val) >> 8)
 #endif
@@ -659,7 +685,7 @@ SCM_DEFINE (scm_kill, "kill", 2, 0, 0,
 #else
   /* Mingw has raise(), but not kill().  (Other raw DOS environments might
      be similar.)  Use raise() when the requested pid is our own process,
-     otherwise bomb.  */
+     otherwise TerminateProcess.  */
   if (scm_to_int (pid) == getpid ())
     {
       if (raise (scm_to_int (sig)) != 0)
@@ -673,6 +699,25 @@ SCM_DEFINE (scm_kill, "kill", 2, 0, 0,
           goto err;
         }
     }
+#ifdef __MINGW32__
+  else
+    {
+      HANDLE ph = OpenProcess (PROCESS_TERMINATE, 0, scm_to_int (pid));
+      int s = scm_to_int (sig);
+
+      if (!ph)
+	{
+	  errno = EPERM;
+	  goto err;
+	}
+      if (!TerminateProcess (ph, win32_signal_to_status (s)))
+	{
+	  errno = EINVAL;
+	  goto err;
+	}
+      CloseHandle (ph);
+    }
+#endif	/* __MINGW32__ */
 #endif
   return SCM_UNSPECIFIED;
 }
@@ -735,7 +780,6 @@ SCM_DEFINE (scm_waitpid, "waitpid", 1, 1
 #undef FUNC_NAME
 #endif /* HAVE_WAITPID */
 
-#ifndef __MINGW32__
 SCM_DEFINE (scm_status_exit_val, "status:exit-val", 1, 0, 0, 
             (SCM status),
 	    "Return the exit status value, as would be set if a process\n"
@@ -786,7 +830,6 @@ SCM_DEFINE (scm_status_stop_sig, "status
     return SCM_BOOL_F;
 }
 #undef FUNC_NAME
-#endif /* __MINGW32__ */
 
 #ifdef HAVE_GETPPID
 SCM_DEFINE (scm_getppid, "getppid", 0, 0, 0,
@@ -801,7 +844,6 @@ SCM_DEFINE (scm_getppid, "getppid", 0, 0
 #endif /* HAVE_GETPPID */
 
 
-#ifndef __MINGW32__
 SCM_DEFINE (scm_getuid, "getuid", 0, 0, 0,
             (),
 	    "Return an integer representing the current real user ID.")
@@ -905,10 +947,8 @@ SCM_DEFINE (scm_seteuid, "seteuid", 1, 0
   return SCM_UNSPECIFIED;
 }
 #undef FUNC_NAME
-#endif /* __MINGW32__ */
 
 
-#ifdef HAVE_SETEGID
 SCM_DEFINE (scm_setegid, "setegid", 1, 0, 0,
             (SCM id),
 	    "Sets the effective group ID to the integer @var{id}, provided the process\n"
@@ -931,7 +971,6 @@ SCM_DEFINE (scm_setegid, "setegid", 1, 0
     
 }
 #undef FUNC_NAME
-#endif
 
 
 #ifdef HAVE_GETPGRP
@@ -1141,7 +1180,7 @@ SCM_DEFINE (scm_execl, "execl", 1, 0, 1,
 
   exec_argv = scm_i_allocate_string_pointers (args);
 
-  execv (exec_file, exec_argv);
+  execv (exec_file, (char const * const *)exec_argv);
   SCM_SYSERROR;
 
   /* not reached.  */
@@ -1170,7 +1209,7 @@ SCM_DEFINE (scm_execlp, "execlp", 1, 0, 
 
   exec_argv = scm_i_allocate_string_pointers (args);
 
-  execvp (exec_file, exec_argv);
+  execvp (exec_file, (char const * const *)exec_argv);
   SCM_SYSERROR;
 
   /* not reached.  */
@@ -1204,7 +1243,8 @@ SCM_DEFINE (scm_execle, "execle", 2, 0, 
   exec_argv = scm_i_allocate_string_pointers (args);
   exec_env = scm_i_allocate_string_pointers (env);
 
-  execve (exec_file, exec_argv, exec_env);
+  execve (exec_file, (char const * const *)exec_argv,
+	  (char const * const *)exec_env);
   SCM_SYSERROR;
 
   /* not reached.  */
@@ -1246,6 +1286,7 @@ SCM_DEFINE (scm_fork, "primitive-fork", 
   return scm_from_int (pid);
 }
 #undef FUNC_NAME
+#endif /* HAVE_FORK */
 
 /* Since Guile uses threads, we have to be very careful to avoid calling
    functions that are not async-signal-safe in the child.  That's why
@@ -1262,7 +1303,9 @@ scm_open_process (SCM mode, SCM prog, SC
   int pid;
   char *exec_file;
   char **exec_argv;
+#ifdef HAVE_FORK
   int max_fd = 1024;
+#endif
 
   exec_file = scm_to_locale_string (prog);
   exec_argv = scm_i_allocate_string_pointers (scm_cons (prog, args));
@@ -1319,12 +1362,28 @@ scm_open_process (SCM mode, SCM prog, SC
   }
 #endif
 
+#ifdef HAVE_FORK
   pid = fork ();
+#elif defined(__MINGW32__)
+  if (!reading)
+    c2p[1] = out;
+  if (!writing)
+    p2c[0] = in;
+  pid = start_child (exec_file, exec_argv, reading, c2p, writing, p2c, err);
+#else
+  close (c2p[0]);
+  close (c2p[1]);
+  close (p2c[0]);
+  close (p2c[1]);
+  free (exec_file);
+  errno = ENOSYS;
+  SCM_SYSERROR;
+#endif	/* HAVE_FORK */
 
   if (pid == -1)
     {
       int errno_save = errno;
-      free (exec_file);
+
       if (reading)
         {
           close (c2p[0]);
@@ -1336,6 +1395,8 @@ scm_open_process (SCM mode, SCM prog, SC
           close (p2c[1]);
         }
       errno = errno_save;
+
+      free (exec_file);
       SCM_SYSERROR;
     }
 
@@ -1345,21 +1406,24 @@ scm_open_process (SCM mode, SCM prog, SC
       SCM read_port = SCM_BOOL_F, write_port = SCM_BOOL_F;
 
       /* There is no sense in catching errors on close().  */
-      if (reading)
+      if (reading) 
         {
           close (c2p[1]);
-          read_port = scm_fdes_to_port (c2p[0], "r0", sym_read_pipe);
+          read_port = scm_fdes_to_port (c2p[0], "r", sym_read_pipe);
+          scm_setvbuf (read_port, scm_from_int (_IONBF), SCM_UNDEFINED);
         }
       if (writing)
         {
           close (p2c[0]);
-          write_port = scm_fdes_to_port (p2c[1], "w0", sym_write_pipe);
+          write_port = scm_fdes_to_port (p2c[1], "w", sym_write_pipe);
+          scm_setvbuf (write_port, scm_from_int (_IONBF), SCM_UNDEFINED);
         }
-
+      
       return scm_values
         (scm_list_3 (read_port, write_port, scm_from_int (pid)));
     }
 
+#ifdef HAVE_FORK
   /* The child.  */
   if (reading)
     close (c2p[0]);
@@ -1408,16 +1472,16 @@ scm_open_process (SCM mode, SCM prog, SC
   if (err > 0)
     {
       char *msg = strerror (errno);
-      fprintf (fdopen (err, "a"), "In execlp of %s: %s\n",
+      fprintf (fdopen (err, "a"), "In execvp of %s: %s\n",
                exec_file, msg);
     }
 
   _exit (EXIT_FAILURE);
+#endif	/* HAVE_FORK */
   /* Not reached.  */
   return SCM_BOOL_F;
 }
 #undef FUNC_NAME
-#endif /* HAVE_FORK */
 
 #ifdef __MINGW32__
 # include "win32-uname.h"
@@ -2235,13 +2299,11 @@ SCM_DEFINE (scm_gethostname, "gethostnam
 #endif /* HAVE_GETHOSTNAME */
 
 \f
-#ifdef HAVE_FORK
 static void
 scm_init_popen (void)
 {
   scm_c_define_gsubr ("open-process", 2, 0, 1, scm_open_process);
 }
-#endif
 
 void
 scm_init_posix ()
@@ -2334,11 +2396,11 @@ scm_init_posix ()
 
 #ifdef HAVE_FORK
   scm_add_feature ("fork");
+#endif	/* HAVE_FORK */
   scm_c_register_extension ("libguile-" SCM_EFFECTIVE_VERSION,
                             "scm_init_popen",
 			    (scm_t_extension_init_func) scm_init_popen,
 			    NULL);
-#endif	/* HAVE_FORK */
 }
 
 /*


--- /dev/null	1970-01-01 02:00:00 +0200
+++ libguile/win32-proc.c	2014-06-29 11:26:08 +0300
@@ -0,0 +1,563 @@
+/* Run a child process with redirected standard handles, without
+   redirecting standard handles of the parent.  This is required in
+   multithreaded programs, where redirecting a standard handle affects
+   all threads.  */
+
+#include <stdlib.h>
+#include <string.h>
+
+/* Prepare a possibly redirected file handle to be passed to a child
+   process.  The handle is for the file/device open on file descriptor
+   FD; if FD is invalid, use the null device instead.
+
+   USE_STD non-zero means we have been passed the descriptor used by
+   the parent.
+
+   ACCESS is the Windows access mode for opening the null device.
+
+   Returns the Win32 handle to be passed to CreateProcess.  */
+static HANDLE
+prepare_child_handle (int fd, int use_std, DWORD access)
+{
+  HANDLE htem, hret;
+  DWORD err = 0;
+
+  /* Start with the descriptor, if specified by the caller and valid,
+     otherwise open the null device.  */
+  if (fd < 0)
+    htem = INVALID_HANDLE_VALUE;
+  else
+    htem = (HANDLE)_get_osfhandle (fd);
+
+  /* Duplicate the handle and make it inheritable.  */
+  if (DuplicateHandle (GetCurrentProcess (),
+		       htem,
+		       GetCurrentProcess (),
+		       &hret,
+		       0,
+		       TRUE,
+		       DUPLICATE_SAME_ACCESS) == FALSE)
+    {
+      /* If the original standard handle was invalid (happens, e.g.,
+	 in GUI programs), open the null device instead.  */
+      if ((err = GetLastError ()) == ERROR_INVALID_HANDLE
+	  && use_std)
+	{
+	  htem = CreateFile ("NUL", access,
+			     FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
+			     OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+	  if (htem != INVALID_HANDLE_VALUE
+	      && DuplicateHandle (GetCurrentProcess (),
+				  htem,
+				  GetCurrentProcess (),
+				  &hret,
+				  0,
+				  TRUE,
+				  DUPLICATE_SAME_ACCESS) == FALSE)
+	    {
+	      err = GetLastError ();
+	      CloseHandle (htem);
+	      hret = INVALID_HANDLE_VALUE;
+	    }
+	}
+    }
+
+  if (hret == INVALID_HANDLE_VALUE)
+    {
+      switch (err)
+	{
+	  case ERROR_NO_MORE_FILES:
+	    errno = EMFILE;
+	    break;
+	  case ERROR_INVALID_HANDLE:
+	  default:
+	    errno = EBADF;
+	    break;
+	}
+    }
+
+  return hret;
+}
+
+/* A comparison function for sorting the environment.  */
+static int
+compenv (const void *a1, const void *a2)
+{
+  return stricmp (*((char**)a1), *((char**)a2));
+}
+
+/* Convert the program's 'environ' array to a block of environment
+   variables suitable to be passed to CreateProcess.  This is needed
+   to ensure the child process inherits the up-to-date environment of
+   the parent, including any variables inserted by the parent.  */
+static void
+prepare_envblk (char **envp, char **envblk)
+{
+  char **tmp;
+  int size_needed;
+  int envcnt;
+  char *ptr;
+
+  for (envcnt = 0; envp[envcnt]; envcnt++)
+    ;
+
+  tmp = scm_calloc ((envcnt + 1) * sizeof (*tmp));
+
+  for (envcnt = size_needed = 0; envp[envcnt]; envcnt++)
+    {
+      tmp[envcnt] = envp[envcnt];
+      size_needed += strlen (envp[envcnt]) + 1;
+    }
+  size_needed++;
+
+  /* Windows likes its environment variables sorted.  */
+  qsort ((void *) tmp, (size_t) envcnt, sizeof (char *), compenv);
+
+  /* CreateProcess needs the environment block as a linear array,
+     where each variable is terminated by a null character, and the
+     last one is terminated by 2 null characters.  */
+  ptr = *envblk = scm_calloc (size_needed);
+
+  for (envcnt = 0; tmp[envcnt]; envcnt++)
+    {
+      strcpy (ptr, tmp[envcnt]);
+      ptr += strlen (tmp[envcnt]) + 1;
+    }
+
+  free (tmp);
+}
+
+/* Find an executable PROGRAM on PATH, return result in malloc'ed
+   storage.  If PROGRAM is /bin/sh, and no sh.exe was found on PATH,
+   fall back on the Windows shell and set BIN_SH_REPLACED to non-zero.  */
+static char *
+lookup_cmd (const char *program, int *bin_sh_replaced)
+{
+  static const char *extensions[] = {
+    ".exe", ".cmd", ".bat", "", ".com", NULL
+  };
+  int bin_sh_requested = 0;
+  const char *path;
+  char abs_name[MAX_PATH];
+  DWORD abs_namelen;
+  int i;
+
+  /* If they ask for the Unix system shell, try to find it on PATH.  */
+  if (c_strcasecmp (program, "/bin/sh") == 0)
+    {
+      bin_sh_requested = 1;
+      program = "sh.exe";
+    }
+
+  /* If PROGRAM includes leading directories, the caller already did
+     our job.  */
+  if (strchr (program, '/') != NULL
+      || strchr (program, '\\') != NULL)
+    return scm_strdup (program);
+
+  /* Note: It is OK for getenv below to return NULL -- in that case,
+     SearchPath will search in the directories whose list is specified
+     by the system Registry.  */
+  path = getenv ("PATH");
+  for (i = 0; extensions[i]; i++)
+    {
+      abs_namelen = SearchPath (path, program, extensions[i],
+				MAX_PATH, abs_name, NULL);
+      if (0 < abs_namelen && abs_namelen <= MAX_PATH)	/* found! */
+	break;
+    }
+
+  /* If they asked for /bin/sh and we didn't find it, fall back on the
+     default Windows shell.  */
+  if (abs_namelen <= 0 && bin_sh_requested)
+    {
+      const char *shell = getenv ("ComSpec");
+
+      if (!shell)
+	shell = "C:\\Windows\\system32\\cmd.exe";
+
+      *bin_sh_replaced = 1;
+      strcpy (abs_name, shell);
+      abs_namelen = strlen (abs_name);
+    }
+
+  /* If not found, return the original PROGRAM name.  */
+  if (abs_namelen <= 0 || abs_namelen > MAX_PATH)
+    return scm_strdup (program);
+
+  return scm_strndup (abs_name, abs_namelen);
+}
+
+/* Concatenate command-line arguments in argv[] into a single
+   command-line string, while quoting arguments as needed.  The result
+   is malloc'ed.  */
+static char *
+prepare_cmdline (const char *cmd, const char * const *argv, int bin_sh_replaced)
+{
+  /* These characters should include anything that is special to _any_
+     program, including both Windows and Unixy shells, and the
+     widlcard expansion in startup code of a typical Windows app.  */
+  const char need_quotes[] = " \t#;\"\'*?[]&|<>(){}$`^";
+  size_t cmdlen = 1;	/* for terminating null */
+  char *cmdline = scm_malloc (cmdlen);
+  char *dst = cmdline;
+  int cmd_exe_quoting = 0;
+  int i;
+  const char *p;
+
+  /* Are we constructing a command line for cmd.exe?  */
+  if (bin_sh_replaced)
+    cmd_exe_quoting = 1;
+  else
+    {
+      for (p = cmd + strlen (cmd);
+	   p > cmd && p[-1] != '/' && p[-1] != '\\' && p[-1] != ':';
+	   p--)
+	;
+      if (c_strcasecmp (p, "cmd.exe") == 0
+	  || c_strcasecmp (p, "cmd") == 0)
+	cmd_exe_quoting = 1;
+    }
+
+  /* Initialize the command line to empty.  */
+  *dst = '\0';
+
+  /* Append arguments, if any, from argv[]. */
+  for (i = 0; argv[i]; i++)
+    {
+      const char *src = argv[i];
+      size_t len;
+      int quote_this = 0, n_backslashes = 0;
+      int j;
+
+      /* Append the blank separator.  We don't do that for argv[0]
+	 because that is the command name (will end up in child's
+	 argv[0]), and is only recognized as such if there're no
+	 blanks before it.  */
+      if (i > 0)
+	*dst++ = ' ';
+      len = dst - cmdline;
+
+      /* How much space is required for this argument?  */
+      cmdlen += strlen (argv[i]) + 1; /* 1 for a blank separator */
+      /* cmd.exe needs a different style of quoting: all the arguments
+	 beyond the /c switch are enclosed in an extra pair of quotes,
+	 and not otherwise quoted/escaped. */
+      if (cmd_exe_quoting)
+	{
+	  if (i == 2)
+	    cmdlen += 2;
+	}
+      else if (strpbrk (argv[i], need_quotes))
+	{
+	  quote_this = 1;
+	  cmdlen += 2;
+	  for ( ; *src; src++)
+	    {
+	      /* An embedded quote needs to be escaped by a backslash.
+		 Any backslashes immediately preceding that quote need
+		 each one to be escaped by another backslash.  */
+	      if (*src == '\"')
+		cmdlen += n_backslashes + 1;
+	      if (*src == '\\')
+		n_backslashes++;
+	      else
+		n_backslashes = 0;
+	    }
+	  /* If the closing quote we will add is preceded by
+	     backslashes, those backslashes need to be escaped.  */
+	  cmdlen += n_backslashes;
+	}
+
+      /* Enlarge the command-line string as needed.  */
+      cmdline = scm_realloc (cmdline, cmdlen);
+      dst = cmdline + len;
+
+      if (i == 0
+	  && c_strcasecmp (argv[0], "/bin/sh") == 0
+	  && bin_sh_replaced)
+	{
+	  strcpy (dst, "cmd.exe");
+	  dst += sizeof ("cmd.exe") - 1;
+	  continue;
+	}
+      if (i == 1 && bin_sh_replaced && strcmp (argv[1], "-c") == 0)
+	{
+	  *dst++ = '/';
+	  *dst++ = 'c';
+	  *dst = '\0';
+	  continue;
+	}
+
+      /* Add this argument, possibly quoted, to the command line.  */
+      if (quote_this || (i == 2 && cmd_exe_quoting))
+	*dst++ = '\"';
+      for (src = argv[i]; *src; src++)
+	{
+	  if (quote_this)
+	    {
+	      if (*src == '\"')
+		for (j = n_backslashes + 1; j > 0; j--)
+		  *dst++ = '\\';
+	      if (*src == '\\')
+		n_backslashes++;
+	      else
+		n_backslashes = 0;
+	    }
+	  *dst++ = *src;
+	}
+      if (quote_this)
+	{
+	  for (j = n_backslashes; j > 0; j--)
+	    *dst++ = '\\';
+	  *dst++ = '\"';
+	}
+      *dst = '\0';
+    }
+
+  if (cmd_exe_quoting && i > 2)
+    {
+      /* One extra slot was already reserved when we enlarged cmdlen
+	 by 2 in the "if (cmd_exe_quoting)" clause above.  So we can
+	 safely append a closing quote.  */
+      *dst++ = '\"';
+      *dst = '\0';
+    }
+
+  return cmdline;
+}
+
+/* Start a child process running the program in EXEC_FILE with its
+   standard input and output optionally redirected to a pipe.  ARGV is
+   the array of command-line arguments to pass to the child.  P2C and
+   C2P are 2 pipes for communicating with the child, and ERRFD is the
+   standard error file descriptor to be inherited by the child.
+   READING and WRITING, if non-zero, mean that the corresponding pipe
+   will be used.
+
+   Return the PID of the child process, or -1 if couldn't start a
+   process.  */
+static intptr_t
+start_child (const char *exec_file, char **argv,
+	     int reading, int c2p[2], int writing, int p2c[2], int errfd)
+{
+  HANDLE hin = INVALID_HANDLE_VALUE, hout = INVALID_HANDLE_VALUE;
+  HANDLE herr = INVALID_HANDLE_VALUE;
+  STARTUPINFO si;
+  char *env_block = NULL;
+  char *cmdline = NULL;
+  PROCESS_INFORMATION pi;
+  char *progfile, *p;
+  int errno_save;
+  intptr_t pid;
+  int bin_sh_replaced = 0;
+
+  /* Prepare standard handles to be passed to the child process.  */
+  hin = prepare_child_handle (p2c[0], !writing, GENERIC_READ);
+  if (hin == INVALID_HANDLE_VALUE)
+    return -1;
+  hout = prepare_child_handle (c2p[1], !reading, GENERIC_WRITE);
+  if (hout == INVALID_HANDLE_VALUE)
+    return -1;
+  herr = prepare_child_handle (errfd, 1, GENERIC_WRITE);
+  if (herr == INVALID_HANDLE_VALUE)
+    return -1;
+
+  /* Make sure the parent side of both pipes is not inherited.  This
+     is required because gnulib's 'pipe' creates pipes whose both ends
+     are inheritable, which is traditional on Posix (where pipe
+     descriptors are implicitly duplicated by 'fork'), but wrong on
+     Windows (where pipe handles need to be explicitly
+     duplicated).  */
+  if (writing)
+    SetHandleInformation ((HANDLE)_get_osfhandle (p2c[1]),
+			  HANDLE_FLAG_INHERIT, 0);
+  if (reading)
+    {
+      SetHandleInformation ((HANDLE)_get_osfhandle (c2p[0]),
+			    HANDLE_FLAG_INHERIT, 0);
+      /* Gnulib's 'pipe' opens the pipe in binary mode, but we don't
+	 want to read text-mode input of subprocesses in binary more,
+	 because then we will get the ^M (a.k.a. "CR") characters we
+	 don't expect.  */
+      _setmode (c2p[0], _O_TEXT);
+    }
+
+  /* Set up the startup info for the child, using the parent's as the
+     starting point, and specify in it the redirected handles.  */
+  GetStartupInfo (&si);
+  si.dwFlags = STARTF_USESTDHANDLES;
+  si.lpReserved = 0;
+  si.cbReserved2 = 0;
+  si.lpReserved2 = 0;
+  si.hStdInput = hin;
+  si.hStdOutput = hout;
+  si.hStdError = herr;
+
+  /* Create the environment block for the child.  This is needed
+     because the environment we have in 'environ' is not in the format
+     expected by CreateProcess.  */
+  prepare_envblk (environ, &env_block);
+
+  /* CreateProcess doesn't search PATH, so we must do that for it.  */
+  progfile = lookup_cmd (exec_file, &bin_sh_replaced);
+
+  /* CreateProcess doesn't like forward slashes in the application
+     file name.  */
+  for (p = progfile; *p; p++)
+    if (*p == '/')
+      *p = '\\';
+
+  /* Construct the command line.  */
+  cmdline = prepare_cmdline (exec_file, (const char * const *)argv,
+			     bin_sh_replaced);
+
+  /* All set and ready to fly.  Launch the child process.  */
+  if (!CreateProcess (progfile, cmdline, NULL, NULL, TRUE, 0, env_block, NULL,
+		      &si, &pi))
+    {
+      pid = -1;
+
+      /* Since we use Win32 APIs directly, we need to translate their
+	 errors to errno values by hand.  */
+      switch (GetLastError ())
+	{
+	  case ERROR_FILE_NOT_FOUND:
+	  case ERROR_PATH_NOT_FOUND:
+	  case ERROR_INVALID_DRIVE:
+	  case ERROR_BAD_PATHNAME:
+	    errno = ENOENT;
+	    break;
+	  case ERROR_ACCESS_DENIED:
+	    errno = EACCES;
+	    break;
+	  case ERROR_BAD_ENVIRONMENT:
+	    errno = E2BIG;
+	    break;
+	  case ERROR_BROKEN_PIPE:
+	    errno = EPIPE;
+	    break;
+	  case ERROR_INVALID_HANDLE:
+	    errno = EBADF;
+	    break;
+	  case ERROR_MAX_THRDS_REACHED:
+	    errno = EAGAIN;
+	    break;
+	  case ERROR_BAD_EXE_FORMAT:
+	  case ERROR_BAD_FORMAT:
+	  default:
+	    errno = ENOEXEC;
+	    break;
+	}
+    }
+  else
+    pid = (intptr_t)pi.hProcess;
+
+  errno_save = errno;
+
+  /* Free resources.  */
+  free (progfile);
+  free (cmdline);
+  free (env_block);
+  CloseHandle (hin);
+  CloseHandle (hout);
+  CloseHandle (herr);
+  CloseHandle (pi.hThread);
+
+  /* Posix requires to call the shell if execvp fails to invoke EXEC_FILE.  */
+  if (errno_save == ENOEXEC || errno_save == ENOENT)
+    {
+      const char *shell = getenv ("ComSpec");
+
+      if (!shell)
+	shell = "cmd.exe";
+
+      if (c_strcasecmp (exec_file, shell) != 0)
+	{
+	  argv[0] = (char *)exec_file;
+	  return start_child (shell, argv, reading, c2p, writing, p2c, errfd);
+	}
+    }
+
+  errno = errno_save;
+  return pid;
+}
+
+\f
+/* Emulation of waitpid which only supports WNOHANG, since _cwait doesn't.  */
+int
+waitpid (intptr_t pid, int *status, int options)
+{
+  if ((options & WNOHANG) != 0)
+    {
+      DWORD st;
+
+      if (!GetExitCodeProcess ((HANDLE)pid, &st))
+	{
+	  errno = ECHILD;
+	  return -1;
+	}
+      if (st == STILL_ACTIVE)
+	return 0;
+      if (status)
+	*status = st;
+      return (int)pid;
+    }
+
+  return (int)_cwait (status, pid, WAIT_CHILD);
+}
+
+\f
+/* Translate abnormal exit status of Windows programs into the signal
+   that terminated the program.  This is required to support scm_kill
+   and WTERMSIG.  */
+
+struct signal_and_status {
+  int sig;
+  DWORD status;
+};
+
+static const struct signal_and_status sigtbl[] = {
+  {SIGSEGV, 0xC0000005},	/* access to invalid address */
+  {SIGSEGV, 0xC0000008},	/* invalid handle */
+  {SIGILL,  0xC000001D},	/* illegal instruction */
+  {SIGILL,  0xC0000025},	/* non-continuable instruction */
+  {SIGSEGV, 0xC000008C},	/* array bounds exceeded */
+  {SIGFPE,  0xC000008D},	/* float denormal */
+  {SIGFPE,  0xC000008E},	/* float divide by zero */
+  {SIGFPE,  0xC000008F},	/* float inexact */
+  {SIGFPE,  0xC0000090},	/* float invalid operation */
+  {SIGFPE,  0xC0000091},	/* float overflow */
+  {SIGFPE,  0xC0000092},	/* float stack check */
+  {SIGFPE,  0xC0000093},	/* float underflow */
+  {SIGFPE,  0xC0000094},	/* integer divide by zero */
+  {SIGFPE,  0xC0000095},	/* integer overflow */
+  {SIGILL,  0xC0000096},	/* privileged instruction */
+  {SIGSEGV, 0xC00000FD},	/* stack overflow */
+  {SIGTERM, 0xC000013A},	/* Ctrl-C exit */
+  {SIGINT,  0xC000013A}
+};
+
+static int
+win32_signal_to_status (int sig)
+{
+  int i;
+
+  for (i = 0; i < sizeof (sigtbl) / sizeof (sigtbl[0]); i++)
+    if (sig == sigtbl[i].sig)
+      return sigtbl[i].status;
+
+  return (int)0xC000013A;
+}
+
+static int
+win32_status_to_termsig (DWORD status)
+{
+  int i;
+
+  for (i = 0; i < sizeof (sigtbl) / sizeof (sigtbl[0]); i++)
+    if (status == sigtbl[i].status)
+      return sigtbl[i].sig;
+
+  return SIGTERM;
+}