Background execution + pagination aborts readline/gdb

If pagination occurs as result of output sent as response to a target
event while the target is executing in the background, subsequent
input aborts readline/gdb:

 $ gdb program
 ...
 (gdb) continue&
 Continuing.
 (gdb)
 ---Type <return> to continue, or q <return> to quit---
 *return*
 ---Type <return> to continue, or q <return> to quit---
 Breakpoint 2, after_sleep () at paginate-bg-execution.c:21
 ---Type <return> to continue, or q <return> to quit---
 21        return; /* after sleep */
 p 1
 readline: readline_callback_read_char() called with no handler!
 *abort/SIGABRT*
 $

gdb_readline_wrapper_line removes the handler after a line is
processed.  Usually, we'll end up re-displaying the prompt, and that
reinstalls the handler.  But if the output is coming out of handling
a stop event, we don't re-display the prompt, and nothing restores the
handler.  So the next input wakes up the event loop and calls into
readline, which aborts.

We should do better with the prompt handling while the target is
running (I think we should coordinate with readline, and
hide/redisplay it around output), but that's a more invasive change
better done post 7.8, so this patch is conservative and just
reinstalls the handler as soon as we're out of the readline line
callback.

gdb/
2014-07-14  Pedro Alves  <palves@redhat.com>

	PR gdb/17072
	* top.c (gdb_readline_wrapper_line): Tweak comment.
	(gdb_readline_wrapper_cleanup): If readline is enabled, reinstall
	the input handler callback.

gdb/testsuite/
2014-07-14  Pedro Alves  <palves@redhat.com>

	PR gdb/17072
	* gdb.base/paginate-bg-execution.c: New file.
	* gdb.base/paginate-bg-execution.exp: New file.

gdb/ChangeLog

@@ -1,3 +1,10 @@
+2014-07-14  Pedro Alves  <palves@redhat.com>
+
+	PR gdb/17072
+	* top.c (gdb_readline_wrapper_line): Tweak comment.
+	(gdb_readline_wrapper_cleanup): If readline is enabled, reinstall
+	the input handler callback.
+
 2014-07-14  Pedro Alves  <palves@redhat.com>
 
 	PR gdb/17072

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2014-07-14  Pedro Alves  <palves@redhat.com>
+
+	PR gdb/17072
+	* gdb.base/paginate-bg-execution.c: New file.
+	* gdb.base/paginate-bg-execution.exp: New file.
+
 2014-07-14  Pedro Alves  <palves@redhat.com>
 
 	PR gdb/17072

gdb/testsuite/gdb.base/paginate-bg-execution.c

@@ -0,0 +1,32 @@
+/* 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>
+
+static void
+after_sleep (void)
+{
+  return; /* after sleep */
+}
+
+int
+main (void)
+{
+  sleep (3);
+  after_sleep ();
+  return 0;
+}

gdb/testsuite/gdb.base/paginate-bg-execution.exp

@@ -0,0 +1,127 @@
+# 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/>.
+
+# A collection of tests related to running execution commands directly
+# from the command line, with "-ex".
+
+standard_testfile
+
+if {[build_executable "failed to prepare" $testfile $srcfile debug] == -1} {
+    return -1
+}
+
+# Check that we handle pagination correctly when it triggers due to an
+# background execution command entered directly on the command line.
+
+proc test_bg_execution_pagination_return {} {
+    global binfile
+    global pagination_prompt
+
+    with_test_prefix "paginate" {
+	clean_restart $binfile
+
+	if ![runto_main] then {
+	    fail "Can't run to main"
+	    return 0
+	}
+
+	gdb_test "b after_sleep"
+
+	gdb_test_no_output "set height 2"
+
+	gdb_test "continue&" "Continuing\."
+
+	set test "pagination handled, breakpoint hit"
+	set saw_pagination_prompt 0
+	gdb_test_multiple "" $test {
+	    -re "$pagination_prompt$" {
+		set saw_pagination_prompt 1
+		send_gdb "\n"
+		exp_continue
+	    }
+	    -notransfer -re "<return>" {
+		# Otherwise gdb_test_multiple considers this an
+		# error.
+		exp_continue
+	    }
+	    -re "after sleep\[^\r\n\]+\r\n$" {
+		gdb_assert $saw_pagination_prompt $test
+	    }
+	}
+
+	# GDB used to crash here.
+	gdb_test "p 1" " = 1" "GDB accepts further input"
+
+	# In case the board file wants to send further commands.
+	gdb_test_no_output "set height unlimited"
+    }
+}
+
+# Check that we handle canceling pagination correctly when it triggers
+# due to a background execution command entered directly on the
+# command line.
+
+proc test_bg_execution_pagination_cancel { how } {
+    global binfile
+    global gdb_prompt pagination_prompt
+
+    with_test_prefix "cancel with $how" {
+	clean_restart $binfile
+
+	if ![runto_main] then {
+	    fail "Can't run to main"
+	    return 0
+	}
+
+	gdb_test "b after_sleep"
+
+	gdb_test_no_output "set height 2"
+
+	gdb_test "continue&" "Continuing\."
+
+	set test "continue& paginates"
+	gdb_test_multiple "" $test {
+	    -re "$pagination_prompt$" {
+		pass $test
+	    }
+	    -notransfer -re "<return>" {
+		# Otherwise gdb_test_multiple considers this an error.
+		exp_continue
+	    }
+	}
+
+	set test "cancel pagination"
+	if { $how == "ctrl-c" } {
+	    send_gdb "\003"
+	} else {
+	    send_gdb "q\n"
+
+	}
+	gdb_test_multiple "" $test {
+	    -re "Quit\r\n$gdb_prompt $" {
+		pass $test
+	    }
+	}
+
+	gdb_test "p 1" " = 1" "GDB accepts further input"
+
+	# In case the board file wants to send further commands.
+	gdb_test_no_output "set height unlimited"
+    }
+}
+
+test_bg_execution_pagination_return
+test_bg_execution_pagination_cancel "ctrl-c"
+test_bg_execution_pagination_cancel "quit"

gdb/top.c

@@ -756,7 +756,8 @@ gdb_readline_wrapper_line (char *line)
   after_char_processing_hook = NULL;
 
   /* Prevent parts of the prompt from being redisplayed if annotations
-     are enabled, and readline's state getting out of sync.  */
+     are enabled, and readline's state getting out of sync.  We'll
+     restore it in gdb_readline_wrapper_cleanup.  */
   if (async_command_editing_p)
     rl_callback_handler_remove ();
 }
@@ -776,6 +777,12 @@ gdb_readline_wrapper_cleanup (void *arg)
 
   gdb_assert (input_handler == gdb_readline_wrapper_line);
   input_handler = cleanup->handler_orig;
+
+  /* Reinstall INPUT_HANDLER in readline, without displaying a
+     prompt.  */
+  if (async_command_editing_p)
+    rl_callback_handler_install (NULL, input_handler);
+
   gdb_readline_wrapper_result = NULL;
   gdb_readline_wrapper_done = 0;