CYGWIN file input redirection

CYGWIN file input redirection

[Steve Mucci]

Hello!
I'm an amateur security researcher, and I mainly work with Windows and
the MinGW/CYGWIN/GoW toolset.

I've found in my studies a confirmed bug in the CYGWIN version of gdb;
http://cygwin.com/ml/cygwin/1999-04/msg00308.html

It states that a command such as;
(gdb)run < input.txt
or
(gdb)args < input.txt
do not work.

I've heard that gdb on Windows creates processes with CreateProcess.
Fortunately from what I've found the STARTUPINFO structure contains
a field for standard input called;

HANDLE hStdInput;

Which would allow for directing standard input to I would assume
anything involving a handle.

Since I've also heard that CYGWIN handles the command line differently
than Linux, there are two files in particular that could be useful in solving
this problem located in the CYGWIN source.

target.c //For Linux command line
windows-nat.c //For Windows command line

Here are the MSDN pages for CreateProcess and STARTUPINFO;

https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425(v=vs.85).aspx
https://msdn.microsoft.com/en-us/library/windows/desktop/ms686331(v=vs.85).aspx

How can we fix this bug?

Re: CYGWIN file input redirection

[Eli Zaretskii]

> From: Steve Mucci <samsurfer117@gmail.com>
> Date: Mon, 26 Sep 2016 08:43:36 -0400
> 
> Here are the MSDN pages for CreateProcess and STARTUPINFO;
> 
> https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425(v=vs.85).aspx
> https://msdn.microsoft.com/en-us/library/windows/desktop/ms686331(v=vs.85).aspx
> 
> How can we fix this bug?

Someone needs to write and submit the code to (a) parse the command
line, like "run < foo >> bar 2> baz" and glean the redirections from
it; and (b) actually implement the redirection in the CreateProcess
call.

Re: CYGWIN file input redirection

[Eli Zaretskii]

> Date: Fri, 30 Sep 2016 12:22:13 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> CC: gdb-patches@sourceware.org
> 
> > How can we fix this bug?
> 
> Someone needs to write and submit the code to (a) parse the command
> line, like "run < foo >> bar 2> baz" and glean the redirections from
> it; and (b) actually implement the redirection in the CreateProcess
> call.

Guess what? someone just did.

The patches below implement redirection support for native debugging
of MinGW programs.  (I reused some of the code I wrote years ago for
the DJGPP project.)

OK to push to master?

--- gdb/windows-nat.c~1	2016-10-09 12:37:04.538125000 +0300
+++ gdb/windows-nat.c	2016-10-15 14:27:51.966125000 +0300
@@ -2054,6 +2054,166 @@ clear_win32_environment (char **env)
 }
 #endif
 
+#ifndef __CYGWIN__
+
+/* Support routines for redirecting standard handles of the inferior.  */
+
+static int
+redir_open (const char *redir_string, HANDLE *inp, HANDLE *out, HANDLE *err)
+{
+  HANDLE *hdl;
+  int mode, fd;
+  const char *fname = redir_string + 1;;
+
+  switch (*redir_string)
+    {
+    case '<':
+      hdl = inp;
+      mode = O_RDONLY;
+      break;
+    case '1': case '2':
+      fname++;
+      /* FALLTHROUGH */
+    case '>':
+      hdl = (*redir_string == '2') ? err : out;
+      mode = O_WRONLY | O_CREAT;
+      if (*fname == '>')
+	{
+	  fname++;
+	  mode |= O_APPEND;
+	}
+      else
+	mode |= O_TRUNC;
+      break;
+    default:
+      return -1;
+    }
+  fname++;	/* skip the separator space */
+  fd = _open (fname, mode, _S_IREAD | _S_IWRITE);
+  if (fd < 0)
+    return -1;
+  /* _open just sets a flag for O_APPEND, which won't be passed to the
+     inferior, so we need to actually move the file pointer.  */
+  if ((mode & O_APPEND) != 0)
+    _lseek (fd, 0L, SEEK_END);
+  *hdl = (HANDLE)_get_osfhandle (fd);
+  return 0;
+}
+
+static int
+redir_set_redirection (const char *s, HANDLE *inp, HANDLE *out, HANDLE *err)
+{
+  char buf[__PMAX + 5];	/* extra space for redirection string */
+  char *d = buf;
+  const char *start = s;
+  int quote = 0;
+
+  *d++ = *s++;	/* copy the 1st character, < or > or a digit */
+  if ((*start == '>' || *start == '1' || *start == '2')
+      && *s == '>')
+    {
+      *d++ = *s++;
+      if (*s == '>' && *start != '>')
+	*d++ = *s++;
+    }
+  while (isspace (*s))	/* skip whitespace before file name */
+    s++;
+  *d++ = ' ';		/* separate file name with a single space */
+
+  /* Copy the file name.  */
+  while (*s)
+    {
+      /* Remove quoting characters from the file name in buf[].  */
+      if (*s == '"')	/* could support '..' quoting here */
+	{
+	  if (!quote)
+	    quote = *s++;
+	  else if (*s == quote)
+	    {
+	      quote = 0;
+	      s++;
+	    }
+	  else
+	    *d++ = *s++;
+	}
+      else if (*s == '\\')
+	{
+	  if (s[1] == '"')	/* could support '..' here */
+	    s++;
+	  *d++ = *s++;
+	}
+      else if (isspace (*s) && !quote)
+	break;
+      else
+	*d++ = *s++;
+      if (d - buf >= sizeof (buf) - 1)
+	{
+	  errno = ENAMETOOLONG;
+	  return 0;
+	}
+    }
+  *d = '\0';
+
+  /* Windows doesn't allow redirection characters in file names, so we
+     can bail out early if they use them, or if there's no target file
+     name after the redirection symbol.  */
+  if (d[-1] == '>' || d[-1] == '<')
+    {
+      errno = ENOENT;
+      return 0;
+    }
+  if (redir_open (buf, inp, out, err) == 0)
+    return s - start;
+  return 0;
+}
+
+static bool
+redirect_inferior_handles (const char *cmd_orig, char *cmd,
+			   HANDLE *inp, HANDLE *out, HANDLE *err)
+{
+  const char *s = cmd_orig;
+  char *d = cmd;
+  int quote = 0;
+  bool retval = false;
+
+  while (isspace (*s))
+    *d++ = *s++;
+
+  while (*s)
+    {
+      if (*s == '"')	/* could also support '..' quoting here */
+	{
+	  if (!quote)
+	    quote = *s;
+	  else if (*s == quote)
+	    quote = 0;
+	}
+      else if (*s == '\\')
+	{
+	  if (s[1] == '"')	/* escaped quote char */
+	    s++;
+	}
+      else if (!quote)
+	{
+	  if (*s == '<' || *s == '>'
+	      || ((*s == '1' || *s == '2') && s[1] == '>'))
+	    {
+	      int skip = redir_set_redirection (s, inp, out, err);
+
+	      if (skip <= 0)
+		return false;
+	      retval = true;
+	      s += skip;
+	    }
+	}
+      if (*s)
+	*d++ = *s++;
+    }
+  *d = '\0';
+  return retval;
+}
+#endif	/* !__CYGWIN__ */
+
 /* Start an inferior windows child process and sets inferior_ptid to its pid.
    EXEC_FILE is the file to run.
    ALLARGS is a string containing the arguments to the program.
@@ -2076,20 +2236,24 @@ windows_create_inferior (struct target_o
   size_t len;
   int tty;
   int ostdin, ostdout, ostderr;
-#else
+#else  /* !__CYGWIN__ */
   char real_path[__PMAX];
   char shell[__PMAX]; /* Path to shell */
   char *toexec;
-  char *args;
-  size_t args_len;
-  HANDLE tty;
+  char *args, *allargs_copy;
+  size_t args_len, allargs_len;
+  HANDLE tty = INVALID_HANDLE_VALUE;
+  HANDLE inf_stdin = INVALID_HANDLE_VALUE;
+  HANDLE inf_stdout = INVALID_HANDLE_VALUE;
+  HANDLE inf_stderr = INVALID_HANDLE_VALUE;
+  bool redirected = false;
   char *w32env;
   char *temp;
   size_t envlen;
   int i;
   size_t envsize;
   char **env;
-#endif
+#endif	/* !__CYGWIN__ */
   PROCESS_INFORMATION pi;
   BOOL ret;
   DWORD flags = 0;
@@ -2121,7 +2285,7 @@ windows_create_inferior (struct target_o
 	error (_("Error starting executable: %d"), errno);
       cygallargs = (wchar_t *) alloca (len * sizeof (wchar_t));
       mbstowcs (cygallargs, allargs, len);
-#else
+#else  /* !__USEWIDE */
       cygallargs = allargs;
 #endif
     }
@@ -2137,12 +2301,12 @@ windows_create_inferior (struct target_o
 	    + mbstowcs (NULL, allargs, 0) + 2;
       cygallargs = (wchar_t *) alloca (len * sizeof (wchar_t));
       swprintf (cygallargs, len, L" -c 'exec %s %s'", exec_file, allargs);
-#else
+#else  /* !__USEWIDE */
       len = (sizeof (" -c 'exec  '") + strlen (exec_file)
 	     + strlen (allargs) + 2);
       cygallargs = (char *) alloca (len);
       xsnprintf (cygallargs, len, " -c 'exec %s %s'", exec_file, allargs);
-#endif
+#endif	/* __USEWIDE */
       toexec = shell;
       flags |= DEBUG_PROCESS;
     }
@@ -2153,12 +2317,12 @@ windows_create_inferior (struct target_o
   wcscpy (args, toexec);
   wcscat (args, L" ");
   wcscat (args, cygallargs);
-#else
+#else  /* !__USEWIDE */
   args = (cygwin_buf_t *) alloca (strlen (toexec) + strlen (cygallargs) + 2);
   strcpy (args, toexec);
   strcat (args, " ");
   strcat (args, cygallargs);
-#endif
+#endif	/* !__USEWIDE */
 
 #ifdef CW_CVT_ENV_TO_WINENV
   /* First try to create a direct Win32 copy of the POSIX environment. */
@@ -2167,7 +2331,7 @@ windows_create_inferior (struct target_o
     flags |= CREATE_UNICODE_ENVIRONMENT;
   else
     /* If that fails, fall back to old method tweaking GDB's environment. */
-#endif
+#endif	/* CW_CVT_ENV_TO_WINENV */
     {
       /* Reset all Win32 environment variables to avoid leftover on next run. */
       clear_win32_environment (environ);
@@ -2232,21 +2396,26 @@ windows_create_inferior (struct target_o
       close (ostdout);
       close (ostderr);
     }
-#else
-  toexec = exec_file;
-  /* Build the command line, a space-separated list of tokens where
-     the first token is the name of the module to be executed.
-     To avoid ambiguities introduced by spaces in the module name,
-     we quote it.  */
-  args_len = strlen (toexec) + 2 /* quotes */ + strlen (allargs) + 2;
-  args = (char *) alloca (args_len);
-  xsnprintf (args, args_len, "\"%s\" %s", toexec, allargs);
-
-  flags |= DEBUG_ONLY_THIS_PROCESS;
-
-  if (!inferior_io_terminal)
-    tty = INVALID_HANDLE_VALUE;
-  else
+#else  /* !__CYGWIN__ */
+  allargs_len = strlen (allargs);
+  allargs_copy = strcpy ((char *)alloca (allargs_len + 1), allargs);
+  if (strpbrk (allargs_copy, "<>"))
+    {
+      int e = errno;
+      errno = 0;
+      redirected =
+	redirect_inferior_handles (allargs, allargs_copy,
+				   &inf_stdin, &inf_stdout, &inf_stderr);
+      if (errno)
+	warning (_("Warning: Error in redirection: %s."), strerror (errno));
+      else
+	errno = e;
+      allargs_len = strlen (allargs_copy);
+    }
+  if (inferior_io_terminal
+      && !(inf_stdin != INVALID_HANDLE_VALUE
+	   && inf_stdout != INVALID_HANDLE_VALUE
+	   && inf_stderr != INVALID_HANDLE_VALUE))
     {
       SECURITY_ATTRIBUTES sa;
       sa.nLength = sizeof(sa);
@@ -2257,15 +2426,32 @@ windows_create_inferior (struct target_o
       if (tty == INVALID_HANDLE_VALUE)
 	warning (_("Warning: Failed to open TTY %s, error %#x."),
 		 inferior_io_terminal, (unsigned) GetLastError ());
-      else
-	{
-	  si.hStdInput = tty;
-	  si.hStdOutput = tty;
-	  si.hStdError = tty;
-	  si.dwFlags |= STARTF_USESTDHANDLES;
-	}
+    }
+  if (redirected || tty != INVALID_HANDLE_VALUE)
+    {
+      si.hStdInput = inf_stdin == INVALID_HANDLE_VALUE ? tty : inf_stdin;
+      if (si.hStdInput == INVALID_HANDLE_VALUE)
+	si.hStdInput = GetStdHandle (STD_INPUT_HANDLE);
+      si.hStdOutput = inf_stdout == INVALID_HANDLE_VALUE ? tty : inf_stdout;
+      if (si.hStdOutput == INVALID_HANDLE_VALUE)
+	si.hStdOutput = GetStdHandle (STD_OUTPUT_HANDLE);
+      si.hStdError = inf_stderr == INVALID_HANDLE_VALUE ? tty : inf_stderr;
+      if (si.hStdError == INVALID_HANDLE_VALUE)
+	si.hStdError = GetStdHandle (STD_ERROR_HANDLE);
+      si.dwFlags |= STARTF_USESTDHANDLES;
     }
 
+  toexec = exec_file;
+  /* Build the command line, a space-separated list of tokens where
+     the first token is the name of the module to be executed.
+     To avoid ambiguities introduced by spaces in the module name,
+     we quote it.  */
+  args_len = strlen (toexec) + 2 /* quotes */ + allargs_len + 2;
+  args = (char *) alloca (args_len);
+  xsnprintf (args, args_len, "\"%s\" %s", toexec, allargs_copy);
+
+  flags |= DEBUG_ONLY_THIS_PROCESS;
+
   /* CreateProcess takes the environment list as a null terminated set of
      strings (i.e. two nulls terminate the list).  */
 
@@ -2304,7 +2490,13 @@ windows_create_inferior (struct target_o
 			&pi);
   if (tty != INVALID_HANDLE_VALUE)
     CloseHandle (tty);
-#endif
+  if (inf_stdin != INVALID_HANDLE_VALUE)
+    CloseHandle (inf_stdin);
+  if (inf_stdout != INVALID_HANDLE_VALUE)
+    CloseHandle (inf_stdout);
+  if (inf_stderr != INVALID_HANDLE_VALUE)
+    CloseHandle (inf_stderr);
+#endif	/* !__CYGWIN__ */
 
   if (!ret)
     error (_("Error creating process %s, (error %u)."),

Re: CYGWIN file input redirection

[Eli Zaretskii]

> Date: Sat, 15 Oct 2016 14:33:13 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> CC: samsurfer117@gmail.com
> 
> > Date: Fri, 30 Sep 2016 12:22:13 +0300
> > From: Eli Zaretskii <eliz@gnu.org>
> > CC: gdb-patches@sourceware.org
> > 
> > > How can we fix this bug?
> > 
> > Someone needs to write and submit the code to (a) parse the command
> > line, like "run < foo >> bar 2> baz" and glean the redirections from
> > it; and (b) actually implement the redirection in the CreateProcess
> > call.
> 
> Guess what? someone just did.
> 
> The patches below implement redirection support for native debugging
> of MinGW programs.  (I reused some of the code I wrote years ago for
> the DJGPP project.)
> 
> OK to push to master?

Sorry, forgot to attach the ChangeLog entries.  Here's the patch again
with the logs:

2016-10-15  Eli Zaretskii  <eliz@gnu.org>

	Support command-line redirection for Windows native debugging

	* windows-nat.c (redir_open, redir_set_redirection)
	(redirect_inferior_handles) [!__CYGWIN__]: New functions for
	redirecting standard handles of the inferior.
	(windows_create_inferior) [!__CYGWIN__]: Use them to redirect
	standard handles of the inferior based on redirection symbols on
	the command line.

--- gdb/windows-nat.c~1	2016-10-09 12:37:04.538125000 +0300
+++ gdb/windows-nat.c	2016-10-15 14:27:51.966125000 +0300
@@ -2054,6 +2054,166 @@ clear_win32_environment (char **env)
 }
 #endif
 
+#ifndef __CYGWIN__
+
+/* Support routines for redirecting standard handles of the inferior.  */
+
+static int
+redir_open (const char *redir_string, HANDLE *inp, HANDLE *out, HANDLE *err)
+{
+  HANDLE *hdl;
+  int mode, fd;
+  const char *fname = redir_string + 1;;
+
+  switch (*redir_string)
+    {
+    case '<':
+      hdl = inp;
+      mode = O_RDONLY;
+      break;
+    case '1': case '2':
+      fname++;
+      /* FALLTHROUGH */
+    case '>':
+      hdl = (*redir_string == '2') ? err : out;
+      mode = O_WRONLY | O_CREAT;
+      if (*fname == '>')
+	{
+	  fname++;
+	  mode |= O_APPEND;
+	}
+      else
+	mode |= O_TRUNC;
+      break;
+    default:
+      return -1;
+    }
+  fname++;	/* skip the separator space */
+  fd = _open (fname, mode, _S_IREAD | _S_IWRITE);
+  if (fd < 0)
+    return -1;
+  /* _open just sets a flag for O_APPEND, which won't be passed to the
+     inferior, so we need to actually move the file pointer.  */
+  if ((mode & O_APPEND) != 0)
+    _lseek (fd, 0L, SEEK_END);
+  *hdl = (HANDLE)_get_osfhandle (fd);
+  return 0;
+}
+
+static int
+redir_set_redirection (const char *s, HANDLE *inp, HANDLE *out, HANDLE *err)
+{
+  char buf[__PMAX + 5];	/* extra space for redirection string */
+  char *d = buf;
+  const char *start = s;
+  int quote = 0;
+
+  *d++ = *s++;	/* copy the 1st character, < or > or a digit */
+  if ((*start == '>' || *start == '1' || *start == '2')
+      && *s == '>')
+    {
+      *d++ = *s++;
+      if (*s == '>' && *start != '>')
+	*d++ = *s++;
+    }
+  while (isspace (*s))	/* skip whitespace before file name */
+    s++;
+  *d++ = ' ';		/* separate file name with a single space */
+
+  /* Copy the file name.  */
+  while (*s)
+    {
+      /* Remove quoting characters from the file name in buf[].  */
+      if (*s == '"')	/* could support '..' quoting here */
+	{
+	  if (!quote)
+	    quote = *s++;
+	  else if (*s == quote)
+	    {
+	      quote = 0;
+	      s++;
+	    }
+	  else
+	    *d++ = *s++;
+	}
+      else if (*s == '\\')
+	{
+	  if (s[1] == '"')	/* could support '..' here */
+	    s++;
+	  *d++ = *s++;
+	}
+      else if (isspace (*s) && !quote)
+	break;
+      else
+	*d++ = *s++;
+      if (d - buf >= sizeof (buf) - 1)
+	{
+	  errno = ENAMETOOLONG;
+	  return 0;
+	}
+    }
+  *d = '\0';
+
+  /* Windows doesn't allow redirection characters in file names, so we
+     can bail out early if they use them, or if there's no target file
+     name after the redirection symbol.  */
+  if (d[-1] == '>' || d[-1] == '<')
+    {
+      errno = ENOENT;
+      return 0;
+    }
+  if (redir_open (buf, inp, out, err) == 0)
+    return s - start;
+  return 0;
+}
+
+static bool
+redirect_inferior_handles (const char *cmd_orig, char *cmd,
+			   HANDLE *inp, HANDLE *out, HANDLE *err)
+{
+  const char *s = cmd_orig;
+  char *d = cmd;
+  int quote = 0;
+  bool retval = false;
+
+  while (isspace (*s))
+    *d++ = *s++;
+
+  while (*s)
+    {
+      if (*s == '"')	/* could also support '..' quoting here */
+	{
+	  if (!quote)
+	    quote = *s;
+	  else if (*s == quote)
+	    quote = 0;
+	}
+      else if (*s == '\\')
+	{
+	  if (s[1] == '"')	/* escaped quote char */
+	    s++;
+	}
+      else if (!quote)
+	{
+	  if (*s == '<' || *s == '>'
+	      || ((*s == '1' || *s == '2') && s[1] == '>'))
+	    {
+	      int skip = redir_set_redirection (s, inp, out, err);
+
+	      if (skip <= 0)
+		return false;
+	      retval = true;
+	      s += skip;
+	    }
+	}
+      if (*s)
+	*d++ = *s++;
+    }
+  *d = '\0';
+  return retval;
+}
+#endif	/* !__CYGWIN__ */
+
 /* Start an inferior windows child process and sets inferior_ptid to its pid.
    EXEC_FILE is the file to run.
    ALLARGS is a string containing the arguments to the program.
@@ -2076,20 +2236,24 @@ windows_create_inferior (struct target_o
   size_t len;
   int tty;
   int ostdin, ostdout, ostderr;
-#else
+#else  /* !__CYGWIN__ */
   char real_path[__PMAX];
   char shell[__PMAX]; /* Path to shell */
   char *toexec;
-  char *args;
-  size_t args_len;
-  HANDLE tty;
+  char *args, *allargs_copy;
+  size_t args_len, allargs_len;
+  HANDLE tty = INVALID_HANDLE_VALUE;
+  HANDLE inf_stdin = INVALID_HANDLE_VALUE;
+  HANDLE inf_stdout = INVALID_HANDLE_VALUE;
+  HANDLE inf_stderr = INVALID_HANDLE_VALUE;
+  bool redirected = false;
   char *w32env;
   char *temp;
   size_t envlen;
   int i;
   size_t envsize;
   char **env;
-#endif
+#endif	/* !__CYGWIN__ */
   PROCESS_INFORMATION pi;
   BOOL ret;
   DWORD flags = 0;
@@ -2121,7 +2285,7 @@ windows_create_inferior (struct target_o
 	error (_("Error starting executable: %d"), errno);
       cygallargs = (wchar_t *) alloca (len * sizeof (wchar_t));
       mbstowcs (cygallargs, allargs, len);
-#else
+#else  /* !__USEWIDE */
       cygallargs = allargs;
 #endif
     }
@@ -2137,12 +2301,12 @@ windows_create_inferior (struct target_o
 	    + mbstowcs (NULL, allargs, 0) + 2;
       cygallargs = (wchar_t *) alloca (len * sizeof (wchar_t));
       swprintf (cygallargs, len, L" -c 'exec %s %s'", exec_file, allargs);
-#else
+#else  /* !__USEWIDE */
       len = (sizeof (" -c 'exec  '") + strlen (exec_file)
 	     + strlen (allargs) + 2);
       cygallargs = (char *) alloca (len);
       xsnprintf (cygallargs, len, " -c 'exec %s %s'", exec_file, allargs);
-#endif
+#endif	/* __USEWIDE */
       toexec = shell;
       flags |= DEBUG_PROCESS;
     }
@@ -2153,12 +2317,12 @@ windows_create_inferior (struct target_o
   wcscpy (args, toexec);
   wcscat (args, L" ");
   wcscat (args, cygallargs);
-#else
+#else  /* !__USEWIDE */
   args = (cygwin_buf_t *) alloca (strlen (toexec) + strlen (cygallargs) + 2);
   strcpy (args, toexec);
   strcat (args, " ");
   strcat (args, cygallargs);
-#endif
+#endif	/* !__USEWIDE */
 
 #ifdef CW_CVT_ENV_TO_WINENV
   /* First try to create a direct Win32 copy of the POSIX environment. */
@@ -2167,7 +2331,7 @@ windows_create_inferior (struct target_o
     flags |= CREATE_UNICODE_ENVIRONMENT;
   else
     /* If that fails, fall back to old method tweaking GDB's environment. */
-#endif
+#endif	/* CW_CVT_ENV_TO_WINENV */
     {
       /* Reset all Win32 environment variables to avoid leftover on next run. */
       clear_win32_environment (environ);
@@ -2232,21 +2396,26 @@ windows_create_inferior (struct target_o
       close (ostdout);
       close (ostderr);
     }
-#else
-  toexec = exec_file;
-  /* Build the command line, a space-separated list of tokens where
-     the first token is the name of the module to be executed.
-     To avoid ambiguities introduced by spaces in the module name,
-     we quote it.  */
-  args_len = strlen (toexec) + 2 /* quotes */ + strlen (allargs) + 2;
-  args = (char *) alloca (args_len);
-  xsnprintf (args, args_len, "\"%s\" %s", toexec, allargs);
-
-  flags |= DEBUG_ONLY_THIS_PROCESS;
-
-  if (!inferior_io_terminal)
-    tty = INVALID_HANDLE_VALUE;
-  else
+#else  /* !__CYGWIN__ */
+  allargs_len = strlen (allargs);
+  allargs_copy = strcpy ((char *)alloca (allargs_len + 1), allargs);
+  if (strpbrk (allargs_copy, "<>"))
+    {
+      int e = errno;
+      errno = 0;
+      redirected =
+	redirect_inferior_handles (allargs, allargs_copy,
+				   &inf_stdin, &inf_stdout, &inf_stderr);
+      if (errno)
+	warning (_("Error in redirection: %s."), strerror (errno));
+      else
+	errno = e;
+      allargs_len = strlen (allargs_copy);
+    }
+  if (inferior_io_terminal
+      && !(inf_stdin != INVALID_HANDLE_VALUE
+	   && inf_stdout != INVALID_HANDLE_VALUE
+	   && inf_stderr != INVALID_HANDLE_VALUE))
     {
       SECURITY_ATTRIBUTES sa;
       sa.nLength = sizeof(sa);
@@ -2257,15 +2426,32 @@ windows_create_inferior (struct target_o
       if (tty == INVALID_HANDLE_VALUE)
 	warning (_("Warning: Failed to open TTY %s, error %#x."),
 		 inferior_io_terminal, (unsigned) GetLastError ());
-      else
-	{
-	  si.hStdInput = tty;
-	  si.hStdOutput = tty;
-	  si.hStdError = tty;
-	  si.dwFlags |= STARTF_USESTDHANDLES;
-	}
+    }
+  if (redirected || tty != INVALID_HANDLE_VALUE)
+    {
+      si.hStdInput = inf_stdin == INVALID_HANDLE_VALUE ? tty : inf_stdin;
+      if (si.hStdInput == INVALID_HANDLE_VALUE)
+	si.hStdInput = GetStdHandle (STD_INPUT_HANDLE);
+      si.hStdOutput = inf_stdout == INVALID_HANDLE_VALUE ? tty : inf_stdout;
+      if (si.hStdOutput == INVALID_HANDLE_VALUE)
+	si.hStdOutput = GetStdHandle (STD_OUTPUT_HANDLE);
+      si.hStdError = inf_stderr == INVALID_HANDLE_VALUE ? tty : inf_stderr;
+      if (si.hStdError == INVALID_HANDLE_VALUE)
+	si.hStdError = GetStdHandle (STD_ERROR_HANDLE);
+      si.dwFlags |= STARTF_USESTDHANDLES;
     }
 
+  toexec = exec_file;
+  /* Build the command line, a space-separated list of tokens where
+     the first token is the name of the module to be executed.
+     To avoid ambiguities introduced by spaces in the module name,
+     we quote it.  */
+  args_len = strlen (toexec) + 2 /* quotes */ + allargs_len + 2;
+  args = (char *) alloca (args_len);
+  xsnprintf (args, args_len, "\"%s\" %s", toexec, allargs_copy);
+
+  flags |= DEBUG_ONLY_THIS_PROCESS;
+
   /* CreateProcess takes the environment list as a null terminated set of
      strings (i.e. two nulls terminate the list).  */
 
@@ -2304,7 +2490,13 @@ windows_create_inferior (struct target_o
 			&pi);
   if (tty != INVALID_HANDLE_VALUE)
     CloseHandle (tty);
-#endif
+  if (inf_stdin != INVALID_HANDLE_VALUE)
+    CloseHandle (inf_stdin);
+  if (inf_stdout != INVALID_HANDLE_VALUE)
+    CloseHandle (inf_stdout);
+  if (inf_stderr != INVALID_HANDLE_VALUE)
+    CloseHandle (inf_stderr);
+#endif	/* !__CYGWIN__ */
 
   if (!ret)
     error (_("Error creating process %s, (error %u)."),

Re: CYGWIN file input redirection

[Eli Zaretskii]

Ping!  Is this OK to push to master, please?

> Date: Sat, 15 Oct 2016 15:39:42 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> CC: samsurfer117@gmail.com
> 
> > Date: Sat, 15 Oct 2016 14:33:13 +0300
> > From: Eli Zaretskii <eliz@gnu.org>
> > CC: samsurfer117@gmail.com
> > 
> > > Date: Fri, 30 Sep 2016 12:22:13 +0300
> > > From: Eli Zaretskii <eliz@gnu.org>
> > > CC: gdb-patches@sourceware.org
> > > 
> > > > How can we fix this bug?
> > > 
> > > Someone needs to write and submit the code to (a) parse the command
> > > line, like "run < foo >> bar 2> baz" and glean the redirections from
> > > it; and (b) actually implement the redirection in the CreateProcess
> > > call.
> > 
> > Guess what? someone just did.
> > 
> > The patches below implement redirection support for native debugging
> > of MinGW programs.  (I reused some of the code I wrote years ago for
> > the DJGPP project.)
> > 
> > OK to push to master?
> 
> Sorry, forgot to attach the ChangeLog entries.  Here's the patch again
> with the logs:
> 
> 2016-10-15  Eli Zaretskii  <eliz@gnu.org>
> 
> 	Support command-line redirection for Windows native debugging
> 
> 	* windows-nat.c (redir_open, redir_set_redirection)
> 	(redirect_inferior_handles) [!__CYGWIN__]: New functions for
> 	redirecting standard handles of the inferior.
> 	(windows_create_inferior) [!__CYGWIN__]: Use them to redirect
> 	standard handles of the inferior based on redirection symbols on
> 	the command line.
> 
> --- gdb/windows-nat.c~1	2016-10-09 12:37:04.538125000 +0300
> +++ gdb/windows-nat.c	2016-10-15 14:27:51.966125000 +0300
> @@ -2054,6 +2054,166 @@ clear_win32_environment (char **env)
>  }
>  #endif
>  
> +#ifndef __CYGWIN__
> +
> +/* Support routines for redirecting standard handles of the inferior.  */
> +
> +static int
> +redir_open (const char *redir_string, HANDLE *inp, HANDLE *out, HANDLE *err)
> +{
> +  HANDLE *hdl;
> +  int mode, fd;
> +  const char *fname = redir_string + 1;;
> +
> +  switch (*redir_string)
> +    {
> +    case '<':
> +      hdl = inp;
> +      mode = O_RDONLY;
> +      break;
> +    case '1': case '2':
> +      fname++;
> +      /* FALLTHROUGH */
> +    case '>':
> +      hdl = (*redir_string == '2') ? err : out;
> +      mode = O_WRONLY | O_CREAT;
> +      if (*fname == '>')
> +	{
> +	  fname++;
> +	  mode |= O_APPEND;
> +	}
> +      else
> +	mode |= O_TRUNC;
> +      break;
> +    default:
> +      return -1;
> +    }
> +  fname++;	/* skip the separator space */
> +  fd = _open (fname, mode, _S_IREAD | _S_IWRITE);
> +  if (fd < 0)
> +    return -1;
> +  /* _open just sets a flag for O_APPEND, which won't be passed to the
> +     inferior, so we need to actually move the file pointer.  */
> +  if ((mode & O_APPEND) != 0)
> +    _lseek (fd, 0L, SEEK_END);
> +  *hdl = (HANDLE)_get_osfhandle (fd);
> +  return 0;
> +}
> +
> +static int
> +redir_set_redirection (const char *s, HANDLE *inp, HANDLE *out, HANDLE *err)
> +{
> +  char buf[__PMAX + 5];	/* extra space for redirection string */
> +  char *d = buf;
> +  const char *start = s;
> +  int quote = 0;
> +
> +  *d++ = *s++;	/* copy the 1st character, < or > or a digit */
> +  if ((*start == '>' || *start == '1' || *start == '2')
> +      && *s == '>')
> +    {
> +      *d++ = *s++;
> +      if (*s == '>' && *start != '>')
> +	*d++ = *s++;
> +    }
> +  while (isspace (*s))	/* skip whitespace before file name */
> +    s++;
> +  *d++ = ' ';		/* separate file name with a single space */
> +
> +  /* Copy the file name.  */
> +  while (*s)
> +    {
> +      /* Remove quoting characters from the file name in buf[].  */
> +      if (*s == '"')	/* could support '..' quoting here */
> +	{
> +	  if (!quote)
> +	    quote = *s++;
> +	  else if (*s == quote)
> +	    {
> +	      quote = 0;
> +	      s++;
> +	    }
> +	  else
> +	    *d++ = *s++;
> +	}
> +      else if (*s == '\\')
> +	{
> +	  if (s[1] == '"')	/* could support '..' here */
> +	    s++;
> +	  *d++ = *s++;
> +	}
> +      else if (isspace (*s) && !quote)
> +	break;
> +      else
> +	*d++ = *s++;
> +      if (d - buf >= sizeof (buf) - 1)
> +	{
> +	  errno = ENAMETOOLONG;
> +	  return 0;
> +	}
> +    }
> +  *d = '\0';
> +
> +  /* Windows doesn't allow redirection characters in file names, so we
> +     can bail out early if they use them, or if there's no target file
> +     name after the redirection symbol.  */
> +  if (d[-1] == '>' || d[-1] == '<')
> +    {
> +      errno = ENOENT;
> +      return 0;
> +    }
> +  if (redir_open (buf, inp, out, err) == 0)
> +    return s - start;
> +  return 0;
> +}
> +
> +static bool
> +redirect_inferior_handles (const char *cmd_orig, char *cmd,
> +			   HANDLE *inp, HANDLE *out, HANDLE *err)
> +{
> +  const char *s = cmd_orig;
> +  char *d = cmd;
> +  int quote = 0;
> +  bool retval = false;
> +
> +  while (isspace (*s))
> +    *d++ = *s++;
> +
> +  while (*s)
> +    {
> +      if (*s == '"')	/* could also support '..' quoting here */
> +	{
> +	  if (!quote)
> +	    quote = *s;
> +	  else if (*s == quote)
> +	    quote = 0;
> +	}
> +      else if (*s == '\\')
> +	{
> +	  if (s[1] == '"')	/* escaped quote char */
> +	    s++;
> +	}
> +      else if (!quote)
> +	{
> +	  if (*s == '<' || *s == '>'
> +	      || ((*s == '1' || *s == '2') && s[1] == '>'))
> +	    {
> +	      int skip = redir_set_redirection (s, inp, out, err);
> +
> +	      if (skip <= 0)
> +		return false;
> +	      retval = true;
> +	      s += skip;
> +	    }
> +	}
> +      if (*s)
> +	*d++ = *s++;
> +    }
> +  *d = '\0';
> +  return retval;
> +}
> +#endif	/* !__CYGWIN__ */
> +
>  /* Start an inferior windows child process and sets inferior_ptid to its pid.
>     EXEC_FILE is the file to run.
>     ALLARGS is a string containing the arguments to the program.
> @@ -2076,20 +2236,24 @@ windows_create_inferior (struct target_o
>    size_t len;
>    int tty;
>    int ostdin, ostdout, ostderr;
> -#else
> +#else  /* !__CYGWIN__ */
>    char real_path[__PMAX];
>    char shell[__PMAX]; /* Path to shell */
>    char *toexec;
> -  char *args;
> -  size_t args_len;
> -  HANDLE tty;
> +  char *args, *allargs_copy;
> +  size_t args_len, allargs_len;
> +  HANDLE tty = INVALID_HANDLE_VALUE;
> +  HANDLE inf_stdin = INVALID_HANDLE_VALUE;
> +  HANDLE inf_stdout = INVALID_HANDLE_VALUE;
> +  HANDLE inf_stderr = INVALID_HANDLE_VALUE;
> +  bool redirected = false;
>    char *w32env;
>    char *temp;
>    size_t envlen;
>    int i;
>    size_t envsize;
>    char **env;
> -#endif
> +#endif	/* !__CYGWIN__ */
>    PROCESS_INFORMATION pi;
>    BOOL ret;
>    DWORD flags = 0;
> @@ -2121,7 +2285,7 @@ windows_create_inferior (struct target_o
>  	error (_("Error starting executable: %d"), errno);
>        cygallargs = (wchar_t *) alloca (len * sizeof (wchar_t));
>        mbstowcs (cygallargs, allargs, len);
> -#else
> +#else  /* !__USEWIDE */
>        cygallargs = allargs;
>  #endif
>      }
> @@ -2137,12 +2301,12 @@ windows_create_inferior (struct target_o
>  	    + mbstowcs (NULL, allargs, 0) + 2;
>        cygallargs = (wchar_t *) alloca (len * sizeof (wchar_t));
>        swprintf (cygallargs, len, L" -c 'exec %s %s'", exec_file, allargs);
> -#else
> +#else  /* !__USEWIDE */
>        len = (sizeof (" -c 'exec  '") + strlen (exec_file)
>  	     + strlen (allargs) + 2);
>        cygallargs = (char *) alloca (len);
>        xsnprintf (cygallargs, len, " -c 'exec %s %s'", exec_file, allargs);
> -#endif
> +#endif	/* __USEWIDE */
>        toexec = shell;
>        flags |= DEBUG_PROCESS;
>      }
> @@ -2153,12 +2317,12 @@ windows_create_inferior (struct target_o
>    wcscpy (args, toexec);
>    wcscat (args, L" ");
>    wcscat (args, cygallargs);
> -#else
> +#else  /* !__USEWIDE */
>    args = (cygwin_buf_t *) alloca (strlen (toexec) + strlen (cygallargs) + 2);
>    strcpy (args, toexec);
>    strcat (args, " ");
>    strcat (args, cygallargs);
> -#endif
> +#endif	/* !__USEWIDE */
>  
>  #ifdef CW_CVT_ENV_TO_WINENV
>    /* First try to create a direct Win32 copy of the POSIX environment. */
> @@ -2167,7 +2331,7 @@ windows_create_inferior (struct target_o
>      flags |= CREATE_UNICODE_ENVIRONMENT;
>    else
>      /* If that fails, fall back to old method tweaking GDB's environment. */
> -#endif
> +#endif	/* CW_CVT_ENV_TO_WINENV */
>      {
>        /* Reset all Win32 environment variables to avoid leftover on next run. */
>        clear_win32_environment (environ);
> @@ -2232,21 +2396,26 @@ windows_create_inferior (struct target_o
>        close (ostdout);
>        close (ostderr);
>      }
> -#else
> -  toexec = exec_file;
> -  /* Build the command line, a space-separated list of tokens where
> -     the first token is the name of the module to be executed.
> -     To avoid ambiguities introduced by spaces in the module name,
> -     we quote it.  */
> -  args_len = strlen (toexec) + 2 /* quotes */ + strlen (allargs) + 2;
> -  args = (char *) alloca (args_len);
> -  xsnprintf (args, args_len, "\"%s\" %s", toexec, allargs);
> -
> -  flags |= DEBUG_ONLY_THIS_PROCESS;
> -
> -  if (!inferior_io_terminal)
> -    tty = INVALID_HANDLE_VALUE;
> -  else
> +#else  /* !__CYGWIN__ */
> +  allargs_len = strlen (allargs);
> +  allargs_copy = strcpy ((char *)alloca (allargs_len + 1), allargs);
> +  if (strpbrk (allargs_copy, "<>"))
> +    {
> +      int e = errno;
> +      errno = 0;
> +      redirected =
> +	redirect_inferior_handles (allargs, allargs_copy,
> +				   &inf_stdin, &inf_stdout, &inf_stderr);
> +      if (errno)
> +	warning (_("Error in redirection: %s."), strerror (errno));
> +      else
> +	errno = e;
> +      allargs_len = strlen (allargs_copy);
> +    }
> +  if (inferior_io_terminal
> +      && !(inf_stdin != INVALID_HANDLE_VALUE
> +	   && inf_stdout != INVALID_HANDLE_VALUE
> +	   && inf_stderr != INVALID_HANDLE_VALUE))
>      {
>        SECURITY_ATTRIBUTES sa;
>        sa.nLength = sizeof(sa);
> @@ -2257,15 +2426,32 @@ windows_create_inferior (struct target_o
>        if (tty == INVALID_HANDLE_VALUE)
>  	warning (_("Warning: Failed to open TTY %s, error %#x."),
>  		 inferior_io_terminal, (unsigned) GetLastError ());
> -      else
> -	{
> -	  si.hStdInput = tty;
> -	  si.hStdOutput = tty;
> -	  si.hStdError = tty;
> -	  si.dwFlags |= STARTF_USESTDHANDLES;
> -	}
> +    }
> +  if (redirected || tty != INVALID_HANDLE_VALUE)
> +    {
> +      si.hStdInput = inf_stdin == INVALID_HANDLE_VALUE ? tty : inf_stdin;
> +      if (si.hStdInput == INVALID_HANDLE_VALUE)
> +	si.hStdInput = GetStdHandle (STD_INPUT_HANDLE);
> +      si.hStdOutput = inf_stdout == INVALID_HANDLE_VALUE ? tty : inf_stdout;
> +      if (si.hStdOutput == INVALID_HANDLE_VALUE)
> +	si.hStdOutput = GetStdHandle (STD_OUTPUT_HANDLE);
> +      si.hStdError = inf_stderr == INVALID_HANDLE_VALUE ? tty : inf_stderr;
> +      if (si.hStdError == INVALID_HANDLE_VALUE)
> +	si.hStdError = GetStdHandle (STD_ERROR_HANDLE);
> +      si.dwFlags |= STARTF_USESTDHANDLES;
>      }
>  
> +  toexec = exec_file;
> +  /* Build the command line, a space-separated list of tokens where
> +     the first token is the name of the module to be executed.
> +     To avoid ambiguities introduced by spaces in the module name,
> +     we quote it.  */
> +  args_len = strlen (toexec) + 2 /* quotes */ + allargs_len + 2;
> +  args = (char *) alloca (args_len);
> +  xsnprintf (args, args_len, "\"%s\" %s", toexec, allargs_copy);
> +
> +  flags |= DEBUG_ONLY_THIS_PROCESS;
> +
>    /* CreateProcess takes the environment list as a null terminated set of
>       strings (i.e. two nulls terminate the list).  */
>  
> @@ -2304,7 +2490,13 @@ windows_create_inferior (struct target_o
>  			&pi);
>    if (tty != INVALID_HANDLE_VALUE)
>      CloseHandle (tty);
> -#endif
> +  if (inf_stdin != INVALID_HANDLE_VALUE)
> +    CloseHandle (inf_stdin);
> +  if (inf_stdout != INVALID_HANDLE_VALUE)
> +    CloseHandle (inf_stdout);
> +  if (inf_stderr != INVALID_HANDLE_VALUE)
> +    CloseHandle (inf_stderr);
> +#endif	/* !__CYGWIN__ */
>  
>    if (!ret)
>      error (_("Error creating process %s, (error %u)."),
> 

Re: CYGWIN file input redirection

[Pedro Alves]

On 10/22/2016 10:30 AM, Eli Zaretskii wrote:
> Ping!  Is this OK to push to master, please?

I think this should have a NEWS entry.  

Since on Windows, programs are expected to handle redirection
themselves, isn't there a chance that this will make it a bit
harder to debug such redirection code in inferiors that
do it themselves?  E.g., imagine if you're debugging cmd.exe's
redirection code.  Or maybe even debugging this new code
in gdb itself?  Do we need a knob to be able to disable
this feature?

I didn't bother to try to understand the patch completely.
I just trust that it works.  It's fine with me to put it in.

It'd be nice to add comments mentioning what syntax works and doesn't
work.  Is there something users should know about syntax, that
should be added to the manual?

Ideally some test would "prove" this all works, which would
also make it possible to more confidently change the implementation
later on if we find it necessary.  It's been years since I'd tried to
run the testsuite for mingw gdb (under cygwin/msys/msys2 of course)
and I have no idea whether people are doing that nowadays.  I have
the impression that maybe no one is..  And then, I can't seem to
find any existing test that exercises redirection, even
on Unix...  :-/  Oh well.

Please see below.

>> 2016-10-15  Eli Zaretskii  <eliz@gnu.org>
>>
>> 	Support command-line redirection for Windows native debugging
>>
>> 	* windows-nat.c (redir_open, redir_set_redirection)
>> 	(redirect_inferior_handles) [!__CYGWIN__]: New functions for
>> 	redirecting standard handles of the inferior.
>> 	(windows_create_inferior) [!__CYGWIN__]: Use them to redirect
>> 	standard handles of the inferior based on redirection symbols on
>> 	the command line.
>>
>> --- gdb/windows-nat.c~1	2016-10-09 12:37:04.538125000 +0300
>> +++ gdb/windows-nat.c	2016-10-15 14:27:51.966125000 +0300
>> @@ -2054,6 +2054,166 @@ clear_win32_environment (char **env)
>>  }
>>  #endif
>>  

>> +  fname++;	/* skip the separator space */
>> +  fd = _open (fname, mode, _S_IREAD | _S_IWRITE);
>> +  if (fd < 0)
>> +    return -1;
>> +  /* _open just sets a flag for O_APPEND, which won't be passed to the
>> +     inferior, so we need to actually move the file pointer.  */
>> +  if ((mode & O_APPEND) != 0)
>> +    _lseek (fd, 0L, SEEK_END);
>> +  *hdl = (HANDLE)_get_osfhandle (fd);

GDB puts a space after casts:

  *hdl = (HANDLE) _get_osfhandle (fd);


>> +  return 0;
>> +}
>> +
>> +static int
>> +redir_set_redirection (const char *s, HANDLE *inp, HANDLE *out, HANDLE *err)

It'd be good to have an intro comment for every new function describing
the interface.  What does this return, for example.

>> +#else  /* !__CYGWIN__ */
>> +  allargs_len = strlen (allargs);
>> +  allargs_copy = strcpy ((char *)alloca (allargs_len + 1), allargs);

Space after cast.

We should really get rid of all unbounded allocas, but it's
preexisting, so you get a pass. :-)

Nit, we already know the length after the strlen call, so
instead of strcpy it could be memcpy.


>> +  if (strpbrk (allargs_copy, "<>"))

      if (strpbrk (allargs_copy, "<>") != NULL)


>> +    {
>> +      int e = errno;
>> +      errno = 0;
>> +      redirected =
>> +	redirect_inferior_handles (allargs, allargs_copy,
>> +				   &inf_stdin, &inf_stdout, &inf_stderr);
>> +      if (errno)
>> +	warning (_("Error in redirection: %s."), strerror (errno));
>> +      else
>> +	errno = e;
>> +      allargs_len = strlen (allargs_copy);
>> +    }
>> +  if (inferior_io_terminal
>> +      && !(inf_stdin != INVALID_HANDLE_VALUE
>> +	   && inf_stdout != INVALID_HANDLE_VALUE
>> +	   && inf_stderr != INVALID_HANDLE_VALUE))

I find these double-negatives hard to read.  I'd suggest:

  if (inferior_io_terminal
      && (inf_stdin == INVALID_HANDLE_VALUE
	  || inf_stdout == INVALID_HANDLE_VALUE
	  || inf_stderr == INVALID_HANDLE_VALUE))

Thanks,
Pedro Alves

Re: CYGWIN file input redirection

[Eli Zaretskii]

> Cc: samsurfer117@gmail.com
> From: Pedro Alves <palves@redhat.com>
> Date: Mon, 24 Oct 2016 13:36:34 +0100
> 
> On 10/22/2016 10:30 AM, Eli Zaretskii wrote:
> > Ping!  Is this OK to push to master, please?
> 
> I think this should have a NEWS entry.  

Yes, I thought about this myself.  Will do.

> Since on Windows, programs are expected to handle redirection
> themselves

??? No, they don't (I believe you thought about wildcard expansion?).
Redirection on Windows shell command line works like on Unix: the
shell invokes the program with standard streams redirected according
to the redirection symbols.  Which is exactly what this code emulates
inside GDB.

> isn't there a chance that this will make it a bit
> harder to debug such redirection code in inferiors that
> do it themselves?  E.g., imagine if you're debugging cmd.exe's
> redirection code.  Or maybe even debugging this new code
> in gdb itself?  Do we need a knob to be able to disable
> this feature?

I'm not sure I see the problem.  If you debug GDB's redirection code,
you will probably not redirect that GDB's standard streams, right?
IOW, you would

  > gdb ./gdb.exe
  (top-gdb) run foo.exe
  (gdb) run < bar > baz

Right?  Or did you mean something else?

> It'd be nice to add comments mentioning what syntax works and doesn't
> work.  Is there something users should know about syntax, that
> should be added to the manual?

The code is supposed to support everything cmd.exe supports, and
nothing else.  Ah, I see I didn't implement the likes of "2>&1".  Will
do.

The only thing beyond what cmd.exe supports is that one can use
Unix-style forward slashes in redirected file names, which comes in
handy because GDB's file-name completion helps.  Not sure if this
should be in the manual.  WDYT?

> Ideally some test would "prove" this all works, which would
> also make it possible to more confidently change the implementation
> later on if we find it necessary.  It's been years since I'd tried to
> run the testsuite for mingw gdb (under cygwin/msys/msys2 of course)
> and I have no idea whether people are doing that nowadays.  I have
> the impression that maybe no one is..  And then, I can't seem to
> find any existing test that exercises redirection, even
> on Unix...  :-/  Oh well.

Right.  I don't have a setup for running the test suite.  I did, of
course, test the code manually.

> >> +  if (inferior_io_terminal
> >> +      && !(inf_stdin != INVALID_HANDLE_VALUE
> >> +	   && inf_stdout != INVALID_HANDLE_VALUE
> >> +	   && inf_stderr != INVALID_HANDLE_VALUE))
> 
> I find these double-negatives hard to read.  I'd suggest:
> 
>   if (inferior_io_terminal
>       && (inf_stdin == INVALID_HANDLE_VALUE
> 	  || inf_stdout == INVALID_HANDLE_VALUE
> 	  || inf_stderr == INVALID_HANDLE_VALUE))

Interesting, I actually find the latter harder to grasp.  The former
says "if not all of the handles are valid".  I can add a macro
VALID_HANDLE, if that would help.

Thanks for the review, I will add the missing bits and fixes and
resubmit.

Re: CYGWIN file input redirection

[Pedro Alves]

On 10/24/2016 02:24 PM, Eli Zaretskii wrote:

> I'm not sure I see the problem.  If you debug GDB's redirection code,
> you will probably not redirect that GDB's standard streams, right?
> IOW, you would
> 
>   > gdb ./gdb.exe
>   (top-gdb) run foo.exe
>   (gdb) run < bar > baz
> 
> Right?  Or did you mean something else?

OK.  I guess I was confused.  So let's just forget my comment.

> 
>> It'd be nice to add comments mentioning what syntax works and doesn't
>> work.  Is there something users should know about syntax, that
>> should be added to the manual?
> 
> The code is supposed to support everything cmd.exe supports, and
> nothing else.  Ah, I see I didn't implement the likes of "2>&1".  Will
> do.
> 
> The only thing beyond what cmd.exe supports is that one can use
> Unix-style forward slashes in redirected file names, which comes in
> handy because GDB's file-name completion helps.  Not sure if this
> should be in the manual.  WDYT?

Seems fine not to mention that, since gdb supports forward slashes
throughout, anyway.  If it didn't support them here probably someone 
would call it a bug.

> 
>> Ideally some test would "prove" this all works, which would
>> also make it possible to more confidently change the implementation
>> later on if we find it necessary.  It's been years since I'd tried to
>> run the testsuite for mingw gdb (under cygwin/msys/msys2 of course)
>> and I have no idea whether people are doing that nowadays.  I have
>> the impression that maybe no one is..  And then, I can't seem to
>> find any existing test that exercises redirection, even
>> on Unix...  :-/  Oh well.
> 
> Right.  I don't have a setup for running the test suite.  I did, of
> course, test the code manually.
> 
>>>> +  if (inferior_io_terminal
>>>> +      && !(inf_stdin != INVALID_HANDLE_VALUE
>>>> +	   && inf_stdout != INVALID_HANDLE_VALUE
>>>> +	   && inf_stderr != INVALID_HANDLE_VALUE))
>>
>> I find these double-negatives hard to read.  I'd suggest:
>>
>>   if (inferior_io_terminal
>>       && (inf_stdin == INVALID_HANDLE_VALUE
>> 	  || inf_stdout == INVALID_HANDLE_VALUE
>> 	  || inf_stderr == INVALID_HANDLE_VALUE))
> 
> Interesting, I actually find the latter harder to grasp.  The former
> says "if not all of the handles are valid".  I can add a macro
> VALID_HANDLE, if that would help.

Leave it be as you had it then.  It was just a minor suggestion.

> 
> Thanks for the review, I will add the missing bits and fixes and
> resubmit.

Thanks,
Pedro Alves

Re: MS-Windows file input redirection, v2

[Eli Zaretskii]

This is version 2 of the patch to support command-line redirection in
native MS-Windows debugging.  (I removed "CYGWIN" from the subject
because the code below only affects the MinGW build; I don't know
enough to do the same for Cygwin, if required, and to test that.)

Changes from previous version:

  . Pedro's comments adjudicated
  . NEWS entry added
  . Added a large commentary describing what is supported

OK to push to master?

commit 3a0b5a89b4b5c53d19f06eca700ed59fcd9c848d
Author:     Eli Zaretskii <eliz@gnu.org>
Date: Sat Oct 29 12:48:21 2016 +0300

    Support command-line redirection in native MS-Windows debugging
    
    gdb/ChangeLog
    2016-10-29  Eli Zaretskii  <eliz@gnu.org>
    
            * NEWS: Mention support for redirection on MS-Windows.
    
            * windows-nat.c (redir_open, redir_set_redirection)
            (redirect_inferior_handles) [!__CYGWIN__]: New functions.
            (windows_create_inferior) [!__CYGWIN__]: Use
            'redirect_inferior_handles' to redirect standard handles of the
            debuggee if the command line requests that.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 3376b1b..b59a749 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,13 @@
+2016-10-29  Eli Zaretskii  <eliz@gnu.org>
+
+	* NEWS: Mention support for redirection on MS-Windows.
+
+	* windows-nat.c (redir_open, redir_set_redirection)
+	(redirect_inferior_handles) [!__CYGWIN__]: New functions.
+	(windows_create_inferior) [!__CYGWIN__]: Use
+	'redirect_inferior_handles' to redirect standard handles of the
+	debuggee if the command line requests that.
+
 2016-10-28  Pedro Alves  <palves@redhat.com>
 
 	* Makefile.in (CXX_DIALECT): Get from configure.
diff --git a/gdb/NEWS b/gdb/NEWS
index 4a61438..5f3ca99 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -9,6 +9,14 @@
   compiler.  The --disable-build-with-cxx configure option has been
   removed.
 
+* Native debugging on MS-Windows supports command-line redirection
+
+  Command-line arguments used for starting programs on MS-Windows can
+  now include redirection symbols supported by native Windows shells,
+  such as '<', '>', '>>', '2>&1', etc.  This affects GDB commands such
+  as "run", "start", and "set args", as well as the corresponding MI
+  features.
+
 * Support for thread names on MS-Windows.
 
   GDB now catches and handles the special exception that programs
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index c6a809b..4b8adac 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -2116,6 +2116,301 @@ clear_win32_environment (char **env)
 }
 #endif
 
+#ifndef __CYGWIN__
+
+/* Redirection of inferior I/O streams for native MS-Windows programs.
+   Unlike on Unix, where this is handled by invoking the inferior via
+   the shell, on MS-Windows we need to emulate the cmd.exe shell.
+
+   The official documentation of the cmd.exe redirection features is here:
+
+     http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/redirection.mspx
+
+   (That page talks about Windows XP, but there's no newer
+   documentation, so we assume later versions of cmd.exe didn't change
+   anything.)
+
+   Caveat: the documentation on that page seems to include a few lies.
+   For example, it describes strange constructs 1<&2 and 2<&1, which
+   seem to work only when 1>&2 resp. 2>&1 would make sense, and so I
+   think the cmd.exe parser of the redirection symbols simply doesn't
+   care about the < vs > distinction in these cases.  Therefore, the
+   supported features are explicitly documented below.
+
+   The emulation below aims at supporting all the valid use cases
+   supported by cmd.exe, which include:
+
+     < FILE    redirect standard input from FILE
+     0< FILE   redirect standard input from FILE
+     <&N       redirect standard input from file descriptor N
+     0<&N      redirect standard input from file descriptor N
+     > FILE    redirect standard output to FILE
+     >> FILE   append standard output to FILE
+     1>> FILE  append standard output to FILE
+     >&N       redirect standard output to file descriptor N
+     1>&N      redirect standard output to file descriptor N
+     >>&N      append standard output to file descriptor N
+     1>>&N     append standard output to file descriptor N
+     2> FILE   redirect standard error to FILE
+     2>> FILE  append standard error to FILE
+     2>&N      redirect standard error to file descriptor N
+     2>>&N     append standard error to file descriptor N
+
+     Note that using N > 2 in the above construct is supported, but
+     requires that the corresponding file descriptor be open by some
+     means elsewhere or outside GDB.  Also note that using ">&0" or
+     "<&2" will generally fail, because the file descriptor redirected
+     from is normally open in an incompatible mode (e.g., FD 0 is open
+     for reading only).  IOW, use of such tricks is not recommended;
+     you are on your own.
+
+     We do NOT support redirection of file descriptors above 2, as in
+     "3>SOME-FILE", because MinGW compiled programs don't (supporting
+     that needs special handling in the startup code that MinGW
+     doesn't have).  Pipes are also not supported.
+
+     As for invalid use cases, where the redirection contains some
+     error, the emulation below will detect that and produce some
+     error and/or failure.  But the behavior in those cases is not
+     bug-for-bug compatible with what cmd.exe does in those cases.
+     That's because what cmd.exe does then is not well defined, and
+     seems to be a side effect of the cmd.exe parsing of the command
+     line more than anything else.  For example, try redirecting to an
+     invalid file name, as in "> foo:bar".
+
+     There are also minor syntactic deviations from what cmd.exe does
+     in some corner cases.  For example, it doesn't support the likes
+     of "> &foo" to mean redirect to file named literally "&foo"; we
+     do support that here, because that, too, sounds like some issue
+     with the cmd.exe parser.  Another nicety is that we support
+     redirection targets that use file names with forward slashes,
+     something cmd.exe doesn't -- this comes in handy since GDB
+     file-name completion can be used when typing the command line for
+     the inferior.  */
+
+/* Support routines for redirecting standard handles of the inferior.  */
+
+/* Parse a single redirection spec, open/duplicate the specified
+   file/fd, and assign the appropriate value to one of the 3 standard
+   file descriptors. */
+static int
+redir_open (const char *redir_string, int *inp, int *out, int *err)
+{
+  int *fd, ref_fd = -2;
+  int mode;
+  const char *fname = redir_string + 1;
+  int rc = *redir_string;
+
+  switch (rc)
+    {
+    case '0':
+      fname++;
+      /* FALLTHROUGH */
+    case '<':
+      fd = inp;
+      mode = O_RDONLY;
+      break;
+    case '1': case '2':
+      fname++;
+      /* FALLTHROUGH */
+    case '>':
+      fd = (rc == '2') ? err : out;
+      mode = O_WRONLY | O_CREAT;
+      if (*fname == '>')
+	{
+	  fname++;
+	  mode |= O_APPEND;
+	}
+      else
+	mode |= O_TRUNC;
+      break;
+    default:
+      return -1;
+    }
+
+  if (*fname == '&' && '0' <= fname[1] && fname[1] <= '9')
+    {
+      /* A reference to a file descriptor.  */
+      char *fdtail;
+      ref_fd = (int) strtol (fname + 1, &fdtail, 10);
+      if (fdtail > fname + 1 && *fdtail == '\0')
+	{
+	  /* Don't allow redirection when open modes are incompatible.  */
+	  if ((ref_fd == 0 && (fd == out || fd == err))
+	      || ((ref_fd == 1 || ref_fd == 2) && fd == inp))
+	    {
+	      errno = EPERM;
+	      return -1;
+	    }
+	  if (ref_fd == 0)
+	    ref_fd = *inp;
+	  else if (ref_fd == 1)
+	    ref_fd = *out;
+	  else if (ref_fd == 2)
+	    ref_fd = *err;
+	}
+      else
+	{
+	  errno = EBADF;
+	  return -1;
+	}
+    }
+  else
+    fname++;	/* skip the separator space */
+  /* If the descriptor is already open, close it.  This allows
+     multiple specs of redirections for the same stream, which is
+     somewhat nonsensical, but still valid and supported by cmd.exe.
+     (But cmd.exe only opens a single file in this case, the one
+     specified by the last redirection spec on the command line.)  */
+  if (*fd >= 0)
+    _close (*fd);
+  if (ref_fd == -2)
+    {
+      *fd = _open (fname, mode, _S_IREAD | _S_IWRITE);
+      if (*fd < 0)
+	return -1;
+    }
+  else if (ref_fd == -1)
+    *fd = -1;	/* reset to default destination */
+  else
+    {
+      *fd = _dup (ref_fd);
+      if (*fd < 0)
+	return -1;
+    }
+  /* _open just sets a flag for O_APPEND, which won't be passed to the
+     inferior, so we need to actually move the file pointer.  */
+  if ((mode & O_APPEND) != 0)
+    _lseek (*fd, 0L, SEEK_END);
+  return 0;
+}
+
+/* Canonicalize a single redirection spec and set up the corresponding
+   file descriptor as specified.  */
+static int
+redir_set_redirection (const char *s, int *inp, int *out, int *err)
+{
+  char buf[__PMAX + 2 + 5]; /* extra space for quotes & redirection string */
+  char *d = buf;
+  const char *start = s;
+  int quote = 0;
+
+  *d++ = *s++;	/* copy the 1st character, < or > or a digit */
+  if ((*start == '>' || *start == '1' || *start == '2')
+      && *s == '>')
+    {
+      *d++ = *s++;
+      if (*s == '>' && *start != '>')
+	*d++ = *s++;
+    }
+  else if (*start == '0' && *s == '<')
+    *d++ = *s++;
+  /* cmd.exe recognizes "&N" only immediately after the redirection symbol.  */
+  if (*s != '&')
+    {
+      while (isspace (*s))  /* skip whitespace before file name */
+	s++;
+      *d++ = ' ';	    /* separate file name with a single space */
+    }
+
+  /* Copy the file name.  */
+  while (*s)
+    {
+      /* Remove quoting characters from the file name in buf[].  */
+      if (*s == '"')	/* could support '..' quoting here */
+	{
+	  if (!quote)
+	    quote = *s++;
+	  else if (*s == quote)
+	    {
+	      quote = 0;
+	      s++;
+	    }
+	  else
+	    *d++ = *s++;
+	}
+      else if (*s == '\\')
+	{
+	  if (s[1] == '"')	/* could support '..' here */
+	    s++;
+	  *d++ = *s++;
+	}
+      else if (isspace (*s) && !quote)
+	break;
+      else
+	*d++ = *s++;
+      if (d - buf >= sizeof (buf) - 1)
+	{
+	  errno = ENAMETOOLONG;
+	  return 0;
+	}
+    }
+  *d = '\0';
+
+  /* Windows doesn't allow redirection characters in file names, so we
+     can bail out early if they use them, or if there's no target file
+     name after the redirection symbol.  */
+  if (d[-1] == '>' || d[-1] == '<')
+    {
+      errno = ENOENT;
+      return 0;
+    }
+  if (redir_open (buf, inp, out, err) == 0)
+    return s - start;
+  return 0;
+}
+
+/* Parse the command line for redirection specs and prepare the file
+   descriptors for the 3 standard streams accordingly.  */
+static bool
+redirect_inferior_handles (const char *cmd_orig, char *cmd,
+			   int *inp, int *out, int *err)
+{
+  const char *s = cmd_orig;
+  char *d = cmd;
+  int quote = 0;
+  bool retval = false;
+
+  while (isspace (*s))
+    *d++ = *s++;
+
+  while (*s)
+    {
+      if (*s == '"')	/* could also support '..' quoting here */
+	{
+	  if (!quote)
+	    quote = *s;
+	  else if (*s == quote)
+	    quote = 0;
+	}
+      else if (*s == '\\')
+	{
+	  if (s[1] == '"')	/* escaped quote char */
+	    s++;
+	}
+      else if (!quote)
+	{
+	  /* Process a single redirection candidate.  */
+	  if (*s == '<' || *s == '>'
+	      || ((*s == '1' || *s == '2') && s[1] == '>')
+	      || (*s == '0' && s[1] == '<'))
+	    {
+	      int skip = redir_set_redirection (s, inp, out, err);
+
+	      if (skip <= 0)
+		return false;
+	      retval = true;
+	      s += skip;
+	    }
+	}
+      if (*s)
+	*d++ = *s++;
+    }
+  *d = '\0';
+  return retval;
+}
+#endif	/* !__CYGWIN__ */
+
 /* Start an inferior windows child process and sets inferior_ptid to its pid.
    EXEC_FILE is the file to run.
    ALLARGS is a string containing the arguments to the program.
@@ -2138,20 +2433,25 @@ windows_create_inferior (struct target_ops *ops, char *exec_file,
   size_t len;
   int tty;
   int ostdin, ostdout, ostderr;
-#else
+#else  /* !__CYGWIN__ */
   char real_path[__PMAX];
   char shell[__PMAX]; /* Path to shell */
   char *toexec;
-  char *args;
-  size_t args_len;
-  HANDLE tty;
+  char *args, *allargs_copy;
+  size_t args_len, allargs_len;
+  int fd_inp = -1, fd_out = -1, fd_err = -1;
+  HANDLE tty = INVALID_HANDLE_VALUE;
+  HANDLE inf_stdin = INVALID_HANDLE_VALUE;
+  HANDLE inf_stdout = INVALID_HANDLE_VALUE;
+  HANDLE inf_stderr = INVALID_HANDLE_VALUE;
+  bool redirected = false;
   char *w32env;
   char *temp;
   size_t envlen;
   int i;
   size_t envsize;
   char **env;
-#endif
+#endif	/* !__CYGWIN__ */
   PROCESS_INFORMATION pi;
   BOOL ret;
   DWORD flags = 0;
@@ -2183,7 +2483,7 @@ windows_create_inferior (struct target_ops *ops, char *exec_file,
 	error (_("Error starting executable: %d"), errno);
       cygallargs = (wchar_t *) alloca (len * sizeof (wchar_t));
       mbstowcs (cygallargs, allargs, len);
-#else
+#else  /* !__USEWIDE */
       cygallargs = allargs;
 #endif
     }
@@ -2199,12 +2499,12 @@ windows_create_inferior (struct target_ops *ops, char *exec_file,
 	    + mbstowcs (NULL, allargs, 0) + 2;
       cygallargs = (wchar_t *) alloca (len * sizeof (wchar_t));
       swprintf (cygallargs, len, L" -c 'exec %s %s'", exec_file, allargs);
-#else
+#else  /* !__USEWIDE */
       len = (sizeof (" -c 'exec  '") + strlen (exec_file)
 	     + strlen (allargs) + 2);
       cygallargs = (char *) alloca (len);
       xsnprintf (cygallargs, len, " -c 'exec %s %s'", exec_file, allargs);
-#endif
+#endif	/* __USEWIDE */
       toexec = shell;
       flags |= DEBUG_PROCESS;
     }
@@ -2215,12 +2515,12 @@ windows_create_inferior (struct target_ops *ops, char *exec_file,
   wcscpy (args, toexec);
   wcscat (args, L" ");
   wcscat (args, cygallargs);
-#else
+#else  /* !__USEWIDE */
   args = (cygwin_buf_t *) alloca (strlen (toexec) + strlen (cygallargs) + 2);
   strcpy (args, toexec);
   strcat (args, " ");
   strcat (args, cygallargs);
-#endif
+#endif	/* !__USEWIDE */
 
 #ifdef CW_CVT_ENV_TO_WINENV
   /* First try to create a direct Win32 copy of the POSIX environment. */
@@ -2229,7 +2529,7 @@ windows_create_inferior (struct target_ops *ops, char *exec_file,
     flags |= CREATE_UNICODE_ENVIRONMENT;
   else
     /* If that fails, fall back to old method tweaking GDB's environment. */
-#endif
+#endif	/* CW_CVT_ENV_TO_WINENV */
     {
       /* Reset all Win32 environment variables to avoid leftover on next run. */
       clear_win32_environment (environ);
@@ -2294,21 +2594,26 @@ windows_create_inferior (struct target_ops *ops, char *exec_file,
       close (ostdout);
       close (ostderr);
     }
-#else
-  toexec = exec_file;
-  /* Build the command line, a space-separated list of tokens where
-     the first token is the name of the module to be executed.
-     To avoid ambiguities introduced by spaces in the module name,
-     we quote it.  */
-  args_len = strlen (toexec) + 2 /* quotes */ + strlen (allargs) + 2;
-  args = (char *) alloca (args_len);
-  xsnprintf (args, args_len, "\"%s\" %s", toexec, allargs);
-
-  flags |= DEBUG_ONLY_THIS_PROCESS;
-
-  if (!inferior_io_terminal)
-    tty = INVALID_HANDLE_VALUE;
-  else
+#else  /* !__CYGWIN__ */
+  allargs_len = strlen (allargs);
+  allargs_copy = strcpy ((char *) alloca (allargs_len + 1), allargs);
+  if (strpbrk (allargs_copy, "<>") != NULL)
+    {
+      int e = errno;
+      errno = 0;
+      redirected =
+	redirect_inferior_handles (allargs, allargs_copy,
+				   &fd_inp, &fd_out, &fd_err);
+      if (errno)
+	warning (_("Error in redirection: %s."), strerror (errno));
+      else
+	errno = e;
+      allargs_len = strlen (allargs_copy);
+    }
+  /* If not all the standard streams are redirected by the command
+     line, use inferior_io_terminal for those which aren't.  */
+  if (inferior_io_terminal
+      && !(fd_inp >= 0 && fd_out >= 0 && fd_err >= 0))
     {
       SECURITY_ATTRIBUTES sa;
       sa.nLength = sizeof(sa);
@@ -2319,15 +2624,41 @@ windows_create_inferior (struct target_ops *ops, char *exec_file,
       if (tty == INVALID_HANDLE_VALUE)
 	warning (_("Warning: Failed to open TTY %s, error %#x."),
 		 inferior_io_terminal, (unsigned) GetLastError ());
+    }
+  if (redirected || tty != INVALID_HANDLE_VALUE)
+    {
+      if (fd_inp >= 0)
+	si.hStdInput = (HANDLE) _get_osfhandle (fd_inp);
+      else if (tty != INVALID_HANDLE_VALUE)
+	si.hStdInput = tty;
       else
-	{
-	  si.hStdInput = tty;
-	  si.hStdOutput = tty;
-	  si.hStdError = tty;
-	  si.dwFlags |= STARTF_USESTDHANDLES;
-	}
+	si.hStdInput = GetStdHandle (STD_INPUT_HANDLE);
+      if (fd_out >= 0)
+	si.hStdOutput = (HANDLE) _get_osfhandle (fd_out);
+      else if (tty != INVALID_HANDLE_VALUE)
+	si.hStdOutput = tty;
+      else
+	si.hStdOutput = GetStdHandle (STD_OUTPUT_HANDLE);
+      if (fd_err >= 0)
+	si.hStdError = (HANDLE) _get_osfhandle (fd_err);
+      else if (tty != INVALID_HANDLE_VALUE)
+	si.hStdError = tty;
+      else
+	si.hStdError = GetStdHandle (STD_ERROR_HANDLE);
+      si.dwFlags |= STARTF_USESTDHANDLES;
     }
 
+  toexec = exec_file;
+  /* Build the command line, a space-separated list of tokens where
+     the first token is the name of the module to be executed.
+     To avoid ambiguities introduced by spaces in the module name,
+     we quote it.  */
+  args_len = strlen (toexec) + 2 /* quotes */ + allargs_len + 2;
+  args = (char *) alloca (args_len);
+  xsnprintf (args, args_len, "\"%s\" %s", toexec, allargs_copy);
+
+  flags |= DEBUG_ONLY_THIS_PROCESS;
+
   /* CreateProcess takes the environment list as a null terminated set of
      strings (i.e. two nulls terminate the list).  */
 
@@ -2366,7 +2697,13 @@ windows_create_inferior (struct target_ops *ops, char *exec_file,
 			&pi);
   if (tty != INVALID_HANDLE_VALUE)
     CloseHandle (tty);
-#endif
+  if (fd_inp >= 0)
+    _close (fd_inp);
+  if (fd_out >= 0)
+    _close (fd_out);
+  if (fd_err >= 0)
+    _close (fd_err);
+#endif	/* !__CYGWIN__ */
 
   if (!ret)
     error (_("Error creating process %s, (error %u)."),

Re: MS-Windows file input redirection, v2

[Pedro Alves]

On 10/29/2016 10:55 AM, Eli Zaretskii wrote:
> This is version 2 of the patch to support command-line redirection in
> native MS-Windows debugging.  (I removed "CYGWIN" from the subject
> because the code below only affects the MinGW build; I don't know
> enough to do the same for Cygwin, if required, and to test that.)
> 
> Changes from previous version:
> 
>   . Pedro's comments adjudicated
>   . NEWS entry added
>   . Added a large commentary describing what is supported
> 
> OK to push to master?

LGTM.  Thanks for the detailed comments!

Thanks,
Pedro Alves

Re: MS-Windows file input redirection, v2

[Eli Zaretskii]

> Cc: gdb-patches@sourceware.org, samsurfer117@gmail.com
> From: Pedro Alves <palves@redhat.com>
> Date: Sat, 29 Oct 2016 16:06:27 +0100
> 
> > Changes from previous version:
> > 
> >   . Pedro's comments adjudicated
> >   . NEWS entry added
> >   . Added a large commentary describing what is supported
> > 
> > OK to push to master?
> 
> LGTM.  Thanks for the detailed comments!

Thanks, pushed to master.