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Re: open-process and related functions for MinGW Guile


From: Eli Zaretskii
Subject: Re: open-process and related functions for MinGW Guile
Date: Sat, 09 Aug 2014 17:13:50 +0300

> Date: Mon, 30 Jun 2014 05:49:52 +0300
> From: Eli Zaretskii <address@hidden>
> Cc: address@hidden, address@hidden

Ping!  I've been waiting for comments from Mark, but those never came.

Meanwhile I implemented the changes requested by Ludo, see the updated
patch below.

I hope this will be finally admitted into the repo.

TIA

> 
> > From: address@hidden (Ludovic Courtès)
> > Cc: Mark H Weaver <address@hidden>,  address@hidden
> > Date: Sun, 29 Jun 2014 22:21:28 +0200
> > 
> > > +#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)
> > 
> > I think this was raised in the previous discussion: it looks a bit like
> > black magic, so there should be a comment explaining why this is needed,
> > how the constants were chosen, etc.
> 
> Most of the magic is gone in this version.  I will add a comment about
> 0xC0000000.
> 
> > > +# 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"
> > 
> > ... what would you think of putting all this in a Gnulib module?  It
> > would benefit all GNU packages and probably get more testing.
> 
> Gnulib already has such a module, but its design and implementation is
> based on wrong premises.  We've been through that with Mark back in
> February.
> 
> And my experience with Gnulib responsiveness hasn't changed much since
> then: 2 tiny patches I submitted were accepted, but a larger patch to
> nl_langinfo, which is very important for Guile, was left without a
> comment for the past 3 weeks.
> 
> > > -#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"
> > 
> > This should be a separate change, and it’s dubious since there could be
> > platforms without setegid.
> 
> Which ones?
> 
> > >    exec_argv = scm_i_allocate_string_pointers (args);
> > >  
> > > -  execv (exec_file, exec_argv);
> > > +  execv (exec_file, (char const * const *)exec_argv);
> > 
> > This should be a separate change (if at all needed.)
> 
> It fixes a compiler warning.
> 
> > > -      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);
> > 
> > This reverts a43fa1b.  Could you explain why it’s needed, and make it a
> > separate patch?
> 
> Ignore this, I wasn't aware a change was made there.
> 
> > > --- /dev/null     1970-01-01 02:00:00 +0200
> > > +++ libguile/win32-proc.c 2014-06-29 11:26:08 +0300
> > 
> > Please call it “w32-proc.c” or “woe32-proc.c”
> 
> I was just following the example of win32-uname.c.
> 
> Thanks for the other feedback.

Here's the updated patch:

--- libguile/posix.c.~1~        2014-02-28 22:01:27.000000000 +0200
+++ libguile/posix.c    2014-08-08 17:27:50.339267200 +0300
@@ -84,6 +84,42 @@
 #if HAVE_SYS_WAIT_H
 # include <sys/wait.h>
 #endif
+#ifdef __MINGW32__
+
+#include <c-strcase.h>
+
+# define WEXITSTATUS(stat_val) ((stat_val) & 255)
+/* MS-Windows programs that crash due to a fatal exception exit with
+   an exit code whose 2 MSB bits are set.  */
+# define WIFEXITED(stat_val)   (((stat_val) & 0xC0000000) == 0)
+# define WIFSIGNALED(stat_val) (((stat_val) & 0xC0000000) == 0xC0000000)
+# define WTERMSIG(stat_val)    w32_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 w32_status_to_termsig (DWORD);
+  static int w32_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);
+
+  typedef DWORD_PTR cpu_set_t;
+
+#define CPU_ZERO(s)     memset(s,0,sizeof(*s))
+#define CPU_ISSET(b,s)  ((*s) & (1U << (b))) != 0
+#define CPU_SET(b,s)    (*s) |= (1U << (b))
+#define CPU_SETSIZE     (8*sizeof(DWORD_PTR))
+
+# include "w32-proc.c"
+#endif /* __MINGW32__ */
+
 #ifndef WEXITSTATUS
 # define WEXITSTATUS(stat_val) ((unsigned)(stat_val) >> 8)
 #endif
@@ -659,7 +695,7 @@ 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 +709,25 @@ 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, w32_signal_to_status (s)))
+       {
+         errno = EINVAL;
+         goto err;
+       }
+      CloseHandle (ph);
+    }
+#endif /* __MINGW32__ */
 #endif
   return SCM_UNSPECIFIED;
 }
@@ -735,7 +790,6 @@ 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 +840,6 @@ 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 +854,6 @@ 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 +957,8 @@ 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 +981,6 @@ SCM_DEFINE (scm_setegid, "setegid", 1, 0
     
 }
 #undef FUNC_NAME
-#endif
 
 
 #ifdef HAVE_GETPGRP
@@ -1141,7 +1190,7 @@ 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 +1219,7 @@ 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 +1253,8 @@ 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 +1296,7 @@ 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 +1313,9 @@ 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 +1372,28 @@ 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 +1405,8 @@ scm_open_process (SCM mode, SCM prog, SC
           close (p2c[1]);
         }
       errno = errno_save;
+
+      free (exec_file);
       SCM_SYSERROR;
     }
 
@@ -1361,7 +1432,8 @@ scm_open_process (SCM mode, SCM prog, SC
       return scm_values
         (scm_list_3 (read_port, write_port, scm_from_int (pid)));
     }
-  
+
+#ifdef HAVE_FORK
   /* The child.  */
   if (reading)
     close (c2p[0]);
@@ -1410,16 +1482,16 @@ 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"


--- /dev/null   1970-01-01 02:00:00 +0200
+++ libguile/w32-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;
+}
+
+
+/* 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);
+}
+
+
+/* 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
+w32_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
+w32_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;
+}






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