Implement "set cwd" command on GDB

This commit adds new "set/show cwd" commands, which are used to
set/show the current working directory of the inferior that will be
started.

The idea here is that "set cwd" will become the de facto way of
setting the inferior's cwd.  Currently, the user can use "cd" for
that, but there are side effects: with "cd", GDB also switches to
another directory, and that can impact the loading of scripts and
other files.  With "set cwd", we separate the logic into a new
command.

To maintain backward compatibility, if the user issues a "cd" command
but doesn't use "set cwd", then the inferior's cwd will still be
changed according to what the user specified.  However, "set cwd" has
precedence over "cd", so it can always be used to override it.

"set cwd" works in the following way:

- If the user sets the inferior's cwd by using "set cwd", then this
  directory is saved into current_inferior ()->cwd and is used when
  the inferior is started (see below).

- If the user doesn't set the inferior's cwd by using "set cwd", but
  rather use the "cd" command as before, then this directory is
  inherited by the inferior because GDB will have chdir'd into it.

On Unix-like hosts, the way the directory is changed before the
inferior execution is by expanding the user set directory before the
fork, and then "chdir" after the call to fork/vfork on
"fork_inferior", but before the actual execution.  On Windows, the
inferior cwd set by the user is passed directly to the CreateProcess
call, which takes care of the actual chdir for us.

This way, we'll make sure that GDB's cwd is not affected by the user
set cwd.

gdb/ChangeLog:
2017-10-04  Sergio Durigan Junior  <sergiodj@redhat.com>

	* NEWS (New commands): Mention "set/show cwd".
	* cli/cli-cmds.c (_initialize_cli_cmds): Mention "set cwd" on
	"cd" command's help text.
	* common/common-inferior.h (get_inferior_cwd): New prototype.
	* infcmd.c (inferior_cwd_scratch): New global variable.
	(set_inferior_cwd): New function.
	(get_inferior_cwd): Likewise.
	(set_cwd_command): Likewise.
	(show_cwd_command): Likewise.
	(_initialize_infcmd): Add "set/show cwd" commands.
	* inferior.h (class inferior) <cwd>: New field.
	* nat/fork-inferior.c: Include "gdb_tilde_expand.h".
	(fork_inferior): Change inferior's cwd before its execution.
	* windows-nat.c (windows_create_inferior): Pass inferior's cwd
	to CreateProcess.

gdb/gdbserver/ChangeLog:
2017-10-04  Sergio Durigan Junior  <sergiodj@redhat.com>

	* inferiors.c (current_inferior_cwd): New global variable.
	(get_inferior_cwd): New function.
	* inferiors.h (struct process_info) <cwd>: New field.

gdb/doc/ChangeLog:
2017-10-04  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.texinfo (Starting your Program) <The working directory.>:
	Mention new "set cwd" command.
	(Working Directory) <Your Program's Working Directory>:
	Rephrase to explain that "set cwd" exists and is the default
	way to change the inferior's cwd.

gdb/testsuite/ChangeLog:
2017-10-04  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.base/set-cwd.c: New file.
	* gdb.base/set-cwd.exp: Likewise.

1 files changed, 21 insertions, 2 deletions

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 3e1894410d..1ef38fb32b 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -66,6 +66,7 @@
 #include "x86-nat.h"
 #include "complaints.h"
 #include "inf-child.h"
+#include "gdb_tilde_expand.h"
 
 #define AdjustTokenPrivileges		dyn_AdjustTokenPrivileges
 #define DebugActiveProcessStop		dyn_DebugActiveProcessStop
@@ -2428,6 +2429,7 @@ windows_create_inferior (struct target_ops *ops, const char *exec_file,
 #ifdef __CYGWIN__
   cygwin_buf_t real_path[__PMAX];
   cygwin_buf_t shell[__PMAX]; /* Path to shell */
+  cygwin_buf_t infcwd[__PMAX];
   const char *sh;
   cygwin_buf_t *toexec;
   cygwin_buf_t *cygallargs;
@@ -2465,6 +2467,17 @@ windows_create_inferior (struct target_ops *ops, const char *exec_file,
   if (!exec_file)
     error (_("No executable specified, use `target exec'."));
 
+  const char *inferior_cwd = get_inferior_cwd ();
+  std::string expanded_infcwd;
+  if (inferior_cwd != NULL)
+    {
+      expanded_infcwd = gdb_tilde_expand (inferior_cwd);
+      /* Mirror slashes on inferior's cwd.  */
+      std::replace (expanded_infcwd.begin (), expanded_infcwd.end (),
+		    '/', '\\');
+      inferior_cwd = expanded_infcwd.c_str ();
+    }
+
   memset (&si, 0, sizeof (si));
   si.cb = sizeof (si);
 
@@ -2514,6 +2527,11 @@ windows_create_inferior (struct target_ops *ops, const char *exec_file,
       flags |= DEBUG_PROCESS;
     }
 
+  if (inferior_cwd != NULL
+      && cygwin_conv_path (CCP_POSIX_TO_WIN_W, inferior_cwd,
+			   infcwd, strlen (inferior_cwd)) < 0)
+    error (_("Error converting inferior cwd: %d"), errno);
+
 #ifdef __USEWIDE
   args = (cygwin_buf_t *) alloca ((wcslen (toexec) + wcslen (cygallargs) + 2)
 				  * sizeof (wchar_t));
@@ -2574,7 +2592,8 @@ windows_create_inferior (struct target_ops *ops, const char *exec_file,
 		       TRUE,	/* inherit handles */
 		       flags,	/* start flags */
 		       w32_env,	/* environment */
-		       NULL,	/* current directory */
+		       inferior_cwd != NULL ? infcwd : NULL, /* current
+								directory */
 		       &si,
 		       &pi);
   if (w32_env)
@@ -2697,7 +2716,7 @@ windows_create_inferior (struct target_ops *ops, const char *exec_file,
 			TRUE,	/* inherit handles */
 			flags,	/* start flags */
 			w32env,	/* environment */
-			NULL,	/* current directory */
+			inferior_cwd, /* current directory */
 			&si,
 			&pi);
   if (tty != INVALID_HANDLE_VALUE)