Canceling pagination caused by execution command from command line aborts readline/gdb

This fixes:

 $ ./gdb program -ex "set height 2" -ex "start"
 ...
 Reading symbols from /home/pedro/gdb/tests/threads...done.
 ---Type <return> to continue, or q <return> to quit---^CQuit  << ctrl-c triggers a Quit

 *type something*
 readline: readline_callback_read_char() called with no handler!
 Aborted
 $

Usually, if an error propagates all the way to the top level, we'll
re-enable stdin, in case the command that was running was a
synchronous command.  That's done in the event loop's actual loop
(event-loop.c:start_event_loop).  However, if a foreground execution
command is run before the event loop starts and throws, nothing is
presently reenabling stdin, which leaves sync_execution set.

When we do start the event loop, because sync_execution is still
(mistakenly) set, display_gdb_prompt removes the readline input
callback, even though stdin is registered in the event loop.  Any
input from here on results in readline aborting.

Such commands are run through catch_command_errors,
catch_command_errors_const, so add the tweak there.

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

	PR gdb/17072
	* main.c: Include event-top.h.
	(handle_command_errors): New function.
	(catch_command_errors, catch_command_errors_const): Use it.

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

	PR gdb/17072
	* gdb.base/paginate-execution-startup.c: New file.
	* gdb.base/paginate-execution-startup.exp: New file.
	* lib/gdb.exp (pagination_prompt): New global.
	(default_gdb_spawn): New procedure, factored out from
	default_gdb_spawn.
	(default_gdb_start): Adjust to call default_gdb_spawn.
	(gdb_spawn): New procedure.

1 files changed, 22 insertions, 8 deletions

diff --git a/gdb/main.c b/gdb/main.c
index 1d77bd3..b51ff89 100644
--- a/gdb/main.c
+++ b/gdb/main.c
@@ -46,6 +46,7 @@
 #include "filenames.h"
 #include "filestuff.h"
 #include <signal.h>
+#include "event-top.h"
 
 /* The selected interpreter.  This will be used as a set command
    variable, so it should always be malloc'ed - since
@@ -337,6 +338,25 @@ captured_command_loop (void *data)
   return 1;
 }
 
+/* Handle command errors thrown from within
+   catch_command_errors/catch_command_errors_const.  */
+
+static int
+handle_command_errors (volatile struct gdb_exception e)
+{
+  if (e.reason < 0)
+    {
+      exception_print (gdb_stderr, e);
+
+      /* If any exception escaped to here, we better enable stdin.
+	 Otherwise, any command that calls async_disable_stdin, and
+	 then throws, will leave stdin inoperable.  */
+      async_enable_stdin ();
+      return 0;
+    }
+  return 1;
+}
+
 /* Type of the command callback passed to catch_command_errors.  */
 
 typedef void (catch_command_errors_ftype) (char *, int);
@@ -353,10 +373,7 @@ catch_command_errors (catch_command_errors_ftype *command,
     {
       command (arg, from_tty);
     }
-  exception_print (gdb_stderr, e);
-  if (e.reason < 0)
-    return 0;
-  return 1;
+  return handle_command_errors (e);
 }
 
 /* Type of the command callback passed to catch_command_errors_const.  */
@@ -375,10 +392,7 @@ catch_command_errors_const (catch_command_errors_const_ftype *command,
     {
       command (arg, from_tty);
     }
-  exception_print (gdb_stderr, e);
-  if (e.reason < 0)
-    return 0;
-  return 1;
+  return handle_command_errors (e);
 }
 
 /* Arguments of --command option and its counterpart.  */