PR gdb/17472: With annotations, input while executing in the foreground crashes readl...

PR gdb/17472: With annotations, input while executing in the foreground crashes readline/GDB

Jan caught an intermittent GDB crash with the annota1.exp test:

 Starting program: .../gdb/testsuite/gdb.base/annota1 ^M
 [...]
 FAIL: gdb.base/annota1.exp: run until main breakpoint (timeout)
 [...]
 readline: readline_callback_read_char() called with no handler!^M
 ERROR: Process no longer exists

All we need to is to continue the inferior in the foreground, and type
a command while the inferior is running.  E.g.:

 (gdb) set annotate 2

 ▒▒pre-prompt
 (gdb)
 ▒▒prompt
 c

 ▒▒post-prompt
 Continuing.

 ▒▒starting

 ▒▒frames-invalid

 *inferior is running now*

 p 1<ret>

 readline: readline_callback_read_char() called with no handler!
 Aborted (core dumped)
 $

When we run a foreground execution command we call
target_terminal_inferior to stop GDB from processing input, and to put
the inferior's terminal settings in effect.  Then we tell readline to
hide the prompt with display_gdb_prompt, which clears readline's input
callback too.  When the target stops, we call target_terminal_ours,
which re-installs stdin in the event loop, and then we redisplay the
prompt, reinstalling the readline callbacks.

However, when annotations are in effect, the "frames-invalid"
annotation code calls target_terminal_ours after 'resume' had already
called target_terminal_inferior:

 (top-gdb) bt
 #0  0x000000000056b82f in annotate_frames_invalid () at gdb/annotate.c:219
 #1  0x000000000072e6cc in reinit_frame_cache () at gdb/frame.c:1705
 #2  0x0000000000594bb9 in registers_changed_ptid (ptid=...) at gdb/regcache.c:612
 #3  0x000000000064cca1 in target_resume (ptid=..., step=1, signal=GDB_SIGNAL_0) at gdb/target.c:2136
 #4  0x00000000005f57af in resume (step=1, sig=GDB_SIGNAL_0) at gdb/infrun.c:2263
 #5  0x00000000005f6051 in proceed (addr=18446744073709551615, siggnal=GDB_SIGNAL_DEFAULT, step=1) at gdb/infrun.c:2613

And then once we hide the prompt and remove readline's input handler
callback, we're in a bad state.  We end up with the target running
supposedly in the foreground, but with stdin still installed on the
event loop.  Any input then calls into readline, which aborts because
no rl_linefunc callback handler is installed:

 Program received signal SIGABRT, Aborted.
 0x0000003b36a35877 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
 56        return INLINE_SYSCALL (tgkill, 3, pid, selftid, sig);

 (top-gdb) bt
 #0  0x0000003b36a35877 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
 #1  0x0000003b36a36f68 in __GI_abort () at abort.c:89
 During symbol reading, debug info gives source 9 included from file at zero line 0.
 During symbol reading, debug info gives command-line macro definition with non-zero line 19: _STDC_PREDEF_H 1.
 #2  0x0000000000784a25 in rl_callback_read_char () at src/readline/callback.c:116
 #3  0x0000000000619111 in rl_callback_read_char_wrapper (client_data=0x0) at src/gdb/event-top.c:167
 #4  0x00000000006194e7 in stdin_event_handler (error=0, client_data=0x0) at src/gdb/event-top.c:373
 #5  0x00000000006180da in handle_file_event (data=...) at src/gdb/event-loop.c:763
 #6  0x00000000006175c1 in process_event () at src/gdb/event-loop.c:340
 #7  0x0000000000617688 in gdb_do_one_event () at src/gdb/event-loop.c:404
 #8  0x00000000006176d8 in start_event_loop () at src/gdb/event-loop.c:429
 #9  0x0000000000619143 in cli_command_loop (data=0x0) at src/gdb/event-top.c:182
 #10 0x000000000060f4c8 in current_interp_command_loop () at src/gdb/interps.c:318
 #11 0x0000000000610691 in captured_command_loop (data=0x0) at src/gdb/main.c:323
 #12 0x000000000060c385 in catch_errors (func=0x610676 <captured_command_loop>, func_args=0x0, errstring=0x900241 "", mask=RETURN_MASK_ALL)
     at src/gdb/exceptions.c:237
 #13 0x0000000000611b8f in captured_main (data=0x7fffffffd7b0) at src/gdb/main.c:1151
 #14 0x000000000060c385 in catch_errors (func=0x610a8e <captured_main>, func_args=0x7fffffffd7b0, errstring=0x900241 "", mask=RETURN_MASK_ALL)
     at src/gdb/exceptions.c:237
 #15 0x0000000000611bb8 in gdb_main (args=0x7fffffffd7b0) at src/gdb/main.c:1159
 #16 0x000000000045ef57 in main (argc=3, argv=0x7fffffffd8b8) at src/gdb/gdb.c:32

The fix is to make the annotation code call target_terminal_inferior
again after printing, if the inferior's settings were in effect.

While at it, when we're doing output only, instead of
target_terminal_ours, we should call target_terminal_ours_for_output.
The latter doesn't actually remove stdin from the event loop, and also
leaves SIGINT forwarded to the target.

New test included.

Tested on x86_64 Fedora 20, native and gdbserver.

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

	PR gdb/17472
	* annotate.c (annotate_breakpoints_invalid): Use
	target_terminal_our_for_output instead of target_terminal_ours.
	Give back the terminal to the target.
	(annotate_frames_invalid): Likewise.

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

	PR gdb/17472
	* gdb.base/annota-input-while-running.c: New file.
	* gdb.base/annota-input-while-running.exp: New file.