Get rid of "gdb_dirbuf" and use "getcwd (NULL, 0)"

Currently we have "current_directory" and "gdb_dirbuf" globals, which
means that we basically have two possible places to consult when we
want to know GDB's current working directory.

This is not ideal and can lead to confusion.  Moreover, the way we're
using "gdb_difbuf" along with "getcwd" is problematic because we
declare the buffer with "1024" elements hardcoded, which does not take
into account longer pathnames that are possible in many filesystems.
Using "PATH_MAX" would also not be a solution because of portability
problems.  Therefore, the best solution is to rely on the fact that
"getcwd (NULL, 0)" will "do the right thing" and return a
heap-allocated string containing the full path.  With the new "getcwd"
module from gnulib, it is now possible to do that without worrying
about breaking some host.

With this patch "current_directory" is now the only place to check for
GDB's cwd.

Reviewed-by: Pedro Alves <palves@redhat.com>

gdb/ChangeLog:
2017-09-22  Sergio Durigan Junior  <sergiodj@redhat.com>

	* cli/cli-cmds.c (pwd_command): Use "getcwd (NULL, 0)".
	(cd_command): Likewise.  Free "current_directory" before
	assigning to it.
	* main.c (captured_main_1): Use "getcwd (NULL, 0)".
	* mi/mi-cmd-env.c (mi_cmd_env_pwd): Likewise.
	* top.c (gdb_dirbuf): Remove global declaration.
	* top.h (gdb_dirbuf): Likewise.

gdb/ChangeLog

@@ -1,3 +1,13 @@
+2017-09-22  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* cli/cli-cmds.c (pwd_command): Use "getcwd (NULL, 0)".
+	(cd_command): Likewise.  Free "current_directory" before
+	assigning to it.
+	* main.c (captured_main_1): Use "getcwd (NULL, 0)".
+	* mi/mi-cmd-env.c (mi_cmd_env_pwd): Likewise.
+	* top.c (gdb_dirbuf): Remove global declaration.
+	* top.h (gdb_dirbuf): Likewise.
+
 2017-09-22  Sergio Durigan Junior  <sergiodj@redhat.com>
 
 	* gnulib/aclocal.m4: Regenerate.

gdb/cli/cli-cmds.c

@@ -384,13 +384,16 @@ pwd_command (char *args, int from_tty)
 {
   if (args)
     error (_("The \"pwd\" command does not take an argument: %s"), args);
-  if (! getcwd (gdb_dirbuf, sizeof (gdb_dirbuf)))
+
+  gdb::unique_xmalloc_ptr<char> cwd (getcwd (NULL, 0));
+
+  if (cwd == NULL)
     error (_("Error finding name of working directory: %s"),
            safe_strerror (errno));
 
-  if (strcmp (gdb_dirbuf, current_directory) != 0)
+  if (strcmp (cwd.get (), current_directory) != 0)
     printf_unfiltered (_("Working directory %s\n (canonically %s).\n"),
-		       current_directory, gdb_dirbuf);
+		       current_directory, cwd.get ());
   else
     printf_unfiltered (_("Working directory %s.\n"), current_directory);
 }
@@ -418,7 +421,8 @@ cd_command (char *dir, int from_tty)
   /* There's too much mess with DOSish names like "d:", "d:.",
      "d:./foo" etc.  Instead of having lots of special #ifdef'ed code,
      simply get the canonicalized name of the current directory.  */
-  dir = getcwd (gdb_dirbuf, sizeof (gdb_dirbuf));
+  gdb::unique_xmalloc_ptr<char> cwd (getcwd (NULL, 0));
+  dir = cwd.get ();
 #endif
 
   len = strlen (dir);
@@ -436,7 +440,10 @@ cd_command (char *dir, int from_tty)
 
   dir_holder.reset (savestring (dir, len));
   if (IS_ABSOLUTE_PATH (dir_holder.get ()))
-    current_directory = dir_holder.release ();
+    {
+      xfree (current_directory);
+      current_directory = dir_holder.release ();
+    }
   else
     {
       if (IS_DIR_SEPARATOR (current_directory[strlen (current_directory) - 1]))

gdb/main.c

@@ -549,11 +549,10 @@ captured_main_1 (struct captured_main_args *context)
     (xstrprintf ("%s: warning: ", gdb_program_name));
   warning_pre_print = tmp_warn_preprint.get ();
 
-  if (! getcwd (gdb_dirbuf, sizeof (gdb_dirbuf)))
+  current_directory = getcwd (NULL, 0);
+  if (current_directory == NULL)
     perror_warning_with_name (_("error finding working directory"));
 
-  current_directory = gdb_dirbuf;
-
   /* Set the sysroot path.  */
   gdb_sysroot = relocate_gdb_directory (TARGET_SYSTEM_ROOT,
 					TARGET_SYSTEM_ROOT_RELOCATABLE);

gdb/mi/mi-cmd-env.c

@@ -74,11 +74,12 @@ mi_cmd_env_pwd (const char *command, char **argv, int argc)
      
   /* Otherwise the mi level is 2 or higher.  */
 
-  if (! getcwd (gdb_dirbuf, sizeof (gdb_dirbuf)))
+  gdb::unique_xmalloc_ptr<char> cwd (getcwd (NULL, 0));
+  if (cwd == NULL)
     error (_("-environment-pwd: error finding name of working directory: %s"),
            safe_strerror (errno));
-    
+
-  uiout->field_string ("cwd", gdb_dirbuf);
+  uiout->field_string ("cwd", cwd.get ());
 }
 
 /* Change working directory.  */

gdb/top.c

@@ -133,9 +133,6 @@ show_confirm (struct ui_file *file, int from_tty,
 
 char *current_directory;
 
-/* The directory name is actually stored here (usually).  */
-char gdb_dirbuf[1024];
-
 /* The last command line executed on the console.  Used for command
    repetitions.  */
 char *saved_command_line;

gdb/top.h

@@ -219,7 +219,6 @@ extern void ui_unregister_input_event_handler (struct ui *ui);
 /* From top.c.  */
 extern char *saved_command_line;
 extern int confirm;
-extern char gdb_dirbuf[1024];
 extern int inhibit_gdbinit;
 extern const char gdbinit[];