PR gdb/17471: Repeating a background command makes it foreground

When we repeat a command, by just pressing <ret>, the input from the
previous command is reused for the new command invocation.

When an execution command strips the "&" out of its incoming argument
string, to detect background execution, we poke a '\0' directly to the
incoming argument string.

Combine both, and a repeat of a background command loses the "&".

This is actually only visible if args other than "&" are specified
(e.g., "c 1&" or "next 2&" or "c -a&"), as in the special case of "&"
alone (e.g. "c&") doesn't actually clobber the incoming string.

Fix this by making strip_bg_char return a new string instead of poking
a hole in the input string.

New test included.

Tested on x86_64 Fedora 20, native and gdbserver.

gdb/
2014-10-17  Pedro Alves  <palves@redhat.com>

	PR gdb/17471
	* infcmd.c (strip_bg_char): Change prototype and rewrite.  Now
	returns a copy of the input.
	(run_command_1, continue_command, step_1, jump_command)
	(signal_command, until_command, advance_command, finish_command)
	(attach_command): Adjust and install a cleanup to free the
	stripped args.

gdb/testsuite/
2014-10-17  Pedro Alves  <palves@redhat.com>

	PR gdb/17471
	* gdb.base/bg-execution-repeat.c: New file.
	* gdb.base/bg-execution-repeat.exp: New file.

5 files changed, 224 insertions, 53 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 3d0b65a..f1a85de 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,15 @@
 2014-10-17  Pedro Alves  <palves@redhat.com>
 
+	PR gdb/17471
+	* infcmd.c (strip_bg_char): Change prototype and rewrite.  Now
+	returns a copy of the input.
+	(run_command_1, continue_command, step_1, jump_command)
+	(signal_command, until_command, advance_command, finish_command)
+	(attach_command): Adjust and install a cleanup to free the
+	stripped args.
+
+2014-10-17  Pedro Alves  <palves@redhat.com>
+
 	PR gdb/17300
 	* infcmd.c (continue_1): If continuing all threads in the
 	foreground, make sure the inferior's terminal settings are put in
diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index d270664..4415b31 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -104,8 +104,6 @@ static void run_no_args_command (char *args, int from_tty);
 
 static void go_command (char *line_no, int from_tty);
 
-static int strip_bg_char (char **);
-
 void _initialize_infcmd (void);
 
 #define ERROR_NO_INFERIOR \
@@ -370,35 +368,40 @@ construct_inferior_arguments (int argc, char **argv)
 }
 
 
-/* This function detects whether or not a '&' character (indicating
-   background execution) has been added as *the last* of the arguments ARGS
-   of a command.  If it has, it removes it and returns 1.  Otherwise it
-   does nothing and returns 0.  */
+/* This function strips the '&' character (indicating background
+   execution) that is added as *the last* of the arguments ARGS of a
+   command.  A copy of the incoming ARGS without the '&' is returned,
+   unless the resulting string after stripping is empty, in which case
+   NULL is returned.  *BG_CHAR_P is an output boolean that indicates
+   whether the '&' character was found.  */
 
-static int
-strip_bg_char (char **args)
+static char *
+strip_bg_char (const char *args, int *bg_char_p)
 {
-  char *p = NULL;
+  const char *p;
 
-  p = strchr (*args, '&');
+  if (args == NULL || *args == '\0')
+    {
+      *bg_char_p = 0;
+      return NULL;
+    }
 
-  if (p)
+  p = args + strlen (args);
+  if (p[-1] == '&')
     {
-      if (p == (*args + strlen (*args) - 1))
-	{
-	  if (strlen (*args) > 1)
-	    {
-	      do
-		p--;
-	      while (*p == ' ' || *p == '\t');
-	      *(p + 1) = '\0';
-	    }
-	  else
-	    *args = 0;
-	  return 1;
-	}
+      p--;
+      while (p > args && isspace (p[-1]))
+	p--;
+
+      *bg_char_p = 1;
+      if (p != args)
+	return savestring (args, p - args);
+      else
+	return NULL;
     }
-  return 0;
+
+  *bg_char_p = 0;
+  return xstrdup (args);
 }
 
 /* Common actions to take after creating any sort of inferior, by any
@@ -527,7 +530,8 @@ run_command_1 (char *args, int from_tty, int tbreak_at_main)
   ptid_t ptid;
   struct ui_out *uiout = current_uiout;
   struct target_ops *run_target;
-  int async_exec = 0;
+  int async_exec;
+  struct cleanup *args_chain;
 
   dont_repeat ();
 
@@ -550,8 +554,8 @@ run_command_1 (char *args, int from_tty, int tbreak_at_main)
   reopen_exec_file ();
   reread_symbols ();
 
-  if (args != NULL)
-    async_exec = strip_bg_char (&args);
+  args = strip_bg_char (args, &async_exec);
+  args_chain = make_cleanup (xfree, args);
 
   /* Do validation and preparation before possibly changing anything
      in the inferior.  */
@@ -597,6 +601,9 @@ run_command_1 (char *args, int from_tty, int tbreak_at_main)
       ui_out_flush (uiout);
     }
 
+  /* Done with ARGS.  */
+  do_cleanups (args_chain);
+
   /* We call get_inferior_args() because we might need to compute
      the value now.  */
   run_target->to_create_inferior (run_target, exec_file, get_inferior_args (),
@@ -770,13 +777,15 @@ continue_1 (int all_threads)
 static void
 continue_command (char *args, int from_tty)
 {
-  int async_exec = 0;
+  int async_exec;
   int all_threads = 0;
+  struct cleanup *args_chain;
+
   ERROR_NO_INFERIOR;
 
   /* Find out whether we must run in the background.  */
-  if (args != NULL)
-    async_exec = strip_bg_char (&args);
+  args = strip_bg_char (args, &async_exec);
+  args_chain = make_cleanup (xfree, args);
 
   prepare_execution_command (&current_target, async_exec);
 
@@ -840,6 +849,9 @@ continue_command (char *args, int from_tty)
 	}
     }
 
+  /* Done with ARGS.  */
+  do_cleanups (args_chain);
+
   if (from_tty)
     printf_filtered (_("Continuing.\n"));
 
@@ -899,21 +911,25 @@ step_1 (int skip_subroutines, int single_inst, char *count_string)
 {
   int count = 1;
   struct cleanup *cleanups = make_cleanup (null_cleanup, NULL);
-  int async_exec = 0;
+  int async_exec;
   int thread = -1;
+  struct cleanup *args_chain;
 
   ERROR_NO_INFERIOR;
   ensure_not_tfind_mode ();
   ensure_valid_thread ();
   ensure_not_running ();
 
-  if (count_string)
-    async_exec = strip_bg_char (&count_string);
+  count_string = strip_bg_char (count_string, &async_exec);
+  args_chain = make_cleanup (xfree, count_string);
 
   prepare_execution_command (&current_target, async_exec);
 
   count = count_string ? parse_and_eval_long (count_string) : 1;
 
+  /* Done with ARGS.  */
+  do_cleanups (args_chain);
+
   if (!single_inst || skip_subroutines)		/* Leave si command alone.  */
     {
       struct thread_info *tp = inferior_thread ();
@@ -1134,7 +1150,8 @@ jump_command (char *arg, int from_tty)
   struct symtab_and_line sal;
   struct symbol *fn;
   struct symbol *sfn;
-  int async_exec = 0;
+  int async_exec;
+  struct cleanup *args_chain;
 
   ERROR_NO_INFERIOR;
   ensure_not_tfind_mode ();
@@ -1142,8 +1159,8 @@ jump_command (char *arg, int from_tty)
   ensure_not_running ();
 
   /* Find out whether we must run in the background.  */
-  if (arg != NULL)
-    async_exec = strip_bg_char (&arg);
+  arg = strip_bg_char (arg, &async_exec);
+  args_chain = make_cleanup (xfree, arg);
 
   prepare_execution_command (&current_target, async_exec);
 
@@ -1159,6 +1176,9 @@ jump_command (char *arg, int from_tty)
   sal = sals.sals[0];
   xfree (sals.sals);
 
+  /* Done with ARGS.  */
+  do_cleanups (args_chain);
+
   if (sal.symtab == 0 && sal.pc == 0)
     error (_("No source file has been specified."));
 
@@ -1227,7 +1247,8 @@ static void
 signal_command (char *signum_exp, int from_tty)
 {
   enum gdb_signal oursig;
-  int async_exec = 0;
+  int async_exec;
+  struct cleanup *args_chain;
 
   dont_repeat ();		/* Too dangerous.  */
   ERROR_NO_INFERIOR;
@@ -1236,8 +1257,8 @@ signal_command (char *signum_exp, int from_tty)
   ensure_not_running ();
 
   /* Find out whether we must run in the background.  */
-  if (signum_exp != NULL)
-    async_exec = strip_bg_char (&signum_exp);
+  signum_exp = strip_bg_char (signum_exp, &async_exec);
+  args_chain = make_cleanup (xfree, signum_exp);
 
   prepare_execution_command (&current_target, async_exec);
 
@@ -1453,7 +1474,8 @@ until_next_command (int from_tty)
 static void
 until_command (char *arg, int from_tty)
 {
-  int async_exec = 0;
+  int async_exec;
+  struct cleanup *args_chain;
 
   ERROR_NO_INFERIOR;
   ensure_not_tfind_mode ();
@@ -1461,8 +1483,8 @@ until_command (char *arg, int from_tty)
   ensure_not_running ();
 
   /* Find out whether we must run in the background.  */
-  if (arg != NULL)
-    async_exec = strip_bg_char (&arg);
+  arg = strip_bg_char (arg, &async_exec);
+  args_chain = make_cleanup (xfree, arg);
 
   prepare_execution_command (&current_target, async_exec);
 
@@ -1470,12 +1492,16 @@ until_command (char *arg, int from_tty)
     until_break_command (arg, from_tty, 0);
   else
     until_next_command (from_tty);
+
+  /* Done with ARGS.  */
+  do_cleanups (args_chain);
 }
 
 static void
 advance_command (char *arg, int from_tty)
 {
-  int async_exec = 0;
+  int async_exec;
+  struct cleanup *args_chain;
 
   ERROR_NO_INFERIOR;
   ensure_not_tfind_mode ();
@@ -1486,12 +1512,15 @@ advance_command (char *arg, int from_tty)
     error_no_arg (_("a location"));
 
   /* Find out whether we must run in the background.  */
-  if (arg != NULL)
-    async_exec = strip_bg_char (&arg);
+  arg = strip_bg_char (arg, &async_exec);
+  args_chain = make_cleanup (xfree, arg);
 
   prepare_execution_command (&current_target, async_exec);
 
   until_break_command (arg, from_tty, 1);
+
+  /* Done with ARGS.  */
+  do_cleanups (args_chain);
 }
 
 /* Return the value of the result of a function at the end of a 'finish'
@@ -1766,8 +1795,8 @@ finish_command (char *arg, int from_tty)
 {
   struct frame_info *frame;
   struct symbol *function;
-
-  int async_exec = 0;
+  int async_exec;
+  struct cleanup *args_chain;
 
   ERROR_NO_INFERIOR;
   ensure_not_tfind_mode ();
@@ -1775,14 +1804,17 @@ finish_command (char *arg, int from_tty)
   ensure_not_running ();
 
   /* Find out whether we must run in the background.  */
-  if (arg != NULL)
-    async_exec = strip_bg_char (&arg);
+  arg = strip_bg_char (arg, &async_exec);
+  args_chain = make_cleanup (xfree, arg);
 
   prepare_execution_command (&current_target, async_exec);
 
   if (arg)
     error (_("The \"finish\" command does not take any arguments."));
 
+  /* Done with ARGS.  */
+  do_cleanups (args_chain);
+
   frame = get_prev_frame (get_selected_frame (_("No selected frame.")));
   if (frame == 0)
     error (_("\"finish\" not meaningful in the outermost frame."));
@@ -2546,7 +2578,8 @@ attach_command_continuation_free_args (void *args)
 void
 attach_command (char *args, int from_tty)
 {
-  int async_exec = 0;
+  int async_exec;
+  struct cleanup *args_chain;
   struct target_ops *attach_target;
 
   dont_repeat ();		/* Not for the faint of heart */
@@ -2567,8 +2600,8 @@ attach_command (char *args, int from_tty)
      this function should probably be moved into target_pre_inferior.  */
   target_pre_inferior (from_tty);
 
-  if (args != NULL)
-    async_exec = strip_bg_char (&args);
+  args = strip_bg_char (args, &async_exec);
+  args_chain = make_cleanup (xfree, args);
 
   attach_target = find_attach_target ();
 
@@ -2582,6 +2615,9 @@ attach_command (char *args, int from_tty)
      shouldn't refer to attach_target again.  */
   attach_target = NULL;
 
+  /* Done with ARGS.  */
+  do_cleanups (args_chain);
+
   /* Set up the "saved terminal modes" of the inferior
      based on what modes we are starting it with.  */
   target_terminal_init ();
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 27aabc6..872fd86 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,11 @@
 2014-10-17  Pedro Alves  <palves@redhat.com>
 
+	PR gdb/17471
+	* gdb.base/bg-execution-repeat.c: New file.
+	* gdb.base/bg-execution-repeat.exp: New file.
+
+2014-10-17  Pedro Alves  <palves@redhat.com>
+
 	PR gdb/17300
 	* gdb.base/continue-all-already-running.c: New file.
 	* gdb.base/continue-all-already-running.exp: New file.
diff --git a/gdb/testsuite/gdb.base/bg-execution-repeat.c b/gdb/testsuite/gdb.base/bg-execution-repeat.c
new file mode 100644
index 0000000..26ab997
--- /dev/null
+++ b/gdb/testsuite/gdb.base/bg-execution-repeat.c
@@ -0,0 +1,33 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2014 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <unistd.h>
+
+int
+foo (void)
+{
+  return 0; /* set break here */
+}
+
+int
+main (void)
+{
+  foo ();
+  sleep (5);
+  foo ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/bg-execution-repeat.exp b/gdb/testsuite/gdb.base/bg-execution-repeat.exp
new file mode 100644
index 0000000..d4eb360
--- /dev/null
+++ b/gdb/testsuite/gdb.base/bg-execution-repeat.exp
@@ -0,0 +1,86 @@
+# Copyright (C) 2014 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test that repeating a background command doesn't lose the "&" in the
+# repeat, turning a background command into a foreground command.  See
+# PR gdb/17471.
+
+standard_testfile
+
+if { [build_executable "failed to prepare" ${testfile} $srcfile] } {
+    return -1
+}
+
+set linenum [gdb_get_line_number "set break here"]
+
+# Run the test proper.  CONTINUE_CMD is the background continue
+# command to issue.
+
+proc test {continue_cmd} {
+    global gdb_prompt
+    global binfile
+    global linenum
+
+    clean_restart $binfile
+
+    if ![runto_main] {
+	return
+    }
+
+    gdb_breakpoint "$linenum"
+
+    set test $continue_cmd
+    gdb_test_multiple $test $test {
+	-re "Continuing\\.\r\n$gdb_prompt " {
+	    # Note no end anchor.  If the breakpoint triggers soon enough
+	    # enough we see further output after the prompt.
+	    pass $test
+	}
+    }
+
+    # Wait for the stop.  Don't expect a prompt, as we had resumed the
+    # inferior in the background.
+    set test "breakpoint hit 1"
+    gdb_test_multiple "" $test {
+	-re "set break here" {
+	    pass $test
+	}
+    }
+
+    # Trigger a repeat.  Buggy GDB used to lose the "&", making this a
+    # foreground command...
+    send_gdb "\n"
+    gdb_test "" "Continuing\\." "repeat bg command"
+
+    # ... and thus further input wouldn't be processed until the target
+    # stopped.
+    gdb_test "print 1" " = 1" "input still accepted"
+
+    # Make sure we see a stop after the print, and not before.  Don't
+    # expect a prompt, as we had resumed the inferior in the background.
+    set test "breakpoint hit 2"
+    gdb_test_multiple "" $test {
+	-re "set break here ..\r\n" {
+	    pass $test
+	}
+    }
+}
+
+# Test with and without extra arguments.
+foreach cmd {"c&" "c 1&"} {
+    with_test_prefix $cmd {
+	test $cmd
+    }
+}