Re: [PATCH v2][PR tui/9765] Fix segfault in asm TUI when reaching end of file

[Shahab Vahedi <shahab dot vahedi at gmail dot com>]

On Fri, Jan 10, 2020 at 12:53:17PM +0000, Pedro Alves wrote:
> I didn't delve deep into the patch, but, I should point out one
> thing -- as described in the PR, it's a problem to let exceptions
> cross ncurses.  Any kind of C++ exception.  So which ncurses callback/entry
> point in gdb were we at?  We need to look into it and make sure that

I have found two different call stacks with this exception. There can be
more.

Call stack 1:
  #0  tui_disassemble (...) at gdb/tui/tui-disasm.c:126
  #1  tui_disasm_window::set_contents (...) at gdb/tui/tui-disasm.c:241
  #2  tui_source_window_base::update_source_window_as_is (...) at
        gdb/tui/tui-winsource.c:184
  #3  tui_source_window_base::update_source_window (...) at
        gdb/tui/tui-winsource.c:173
  #4  tui_update_source_windows_with_addr (...) at
        gdb/tui/tui-winsource.c:207
  #5  tui_set_layout (layout_type=DISASSEM_COMMAND) at
        gdb/tui/tui-layout.c:181
  #6  tui_layout_command (layout_name="asm", from_tty=1) at
        gdb/tui/tui-layout.c:287
  #7  do_const_cfunc (c=, args="asm", from_tty=1) at
        gdb/cli/cli-decode.c:107
  #8  cmd_func (cmd=, args="asm", from_tty=1) at
        gdb/cli/cli-decode.c:1952
  #9  execute_command (p="m", from_tty=1) at gdb/top.c:653
  #10 catch_command_errors (...) at gdb/main.c:401
  #11 captured_main_1 (context=) at gdb/main.c:1168
  #12 captured_main (data=) at gdb/main.c:1193
  #13 gdb_main (args=) at gdb/main.c:1218
  #14 main (argc=4, argv=) at gdb/gdb.c:32

call stack 2:
#0  tui_disassemble (...)
    at gdb/tui/tui-disasm.c:126
#1  tui_find_disassembly_address (...)
    at gdb/tui/tui-disasm.c:157
#2  tui_disasm_window::do_scroll_vertical (this=, num_to_scroll=32)
    at gdb/tui/tui-disasm.c:348
#3  tui_win_info::forward_scroll (this=, num_to_scroll=31)
    at gdb/tui/tui-win.c:476
#4  tui_dispatch_ctrl_char (ch=338) at gdb/tui/tui-io.c:921
#5  tui_getc (fp=<_IO_2_1_stdin_>) at gdb/tui/tui-io.c:1005
#6  rl_read_key () at readline/readline/input.c:495
#7  readline_internal_char () at readline/readline/readline.c:573
#8  rl_callback_read_char () at readline/readline/callback.c:262
#9  gdb_rl_callback_read_char_wrapper_noexcept ()
    at gdb/event-top.c:176
#10 gdb_rl_callback_read_char_wrapper (client_data=)
    at gdb/event-top.c:193
#11 stdin_event_handler (error=0, client_data=) at gdb/event-top.c:515
#12 handle_file_event (file_ptr=, ready_mask=1)
    at gdb/event-loop.c:731
#13 gdb_wait_for_event (block=1) at gdb/event-loop.c:857
#14 gdb_do_one_event () at gdb/event-loop.c:346
#15 start_event_loop () at gdb/event-loop.c:370
#16 captured_command_loop () at gdb/main.c:360
#17 captured_main (data=) at gdb/main.c:1203
#18 gdb_main (args=) at gdb/main.c:1218
#19 main (argc=4, argv=) at gdb/gdb.c:32

> no exceptions are thrown from it back into ncurses.  Above, you're rethrowing
> non-memory exceptions, which is what made me wonder, since it sounds like
> for  example a Ctrl-C at some "wrong" time may bring down GDB.
> For readline, we ended up with TRY_SJLJ/CATCH_SJLJ.

For "call stack 1", other exceptions end up here:
gdb/main.c:
 catch_command_errors (...)
 {
   try
     {
       ...
     }
   catch (const gdb_exception &e)
     {
       return handle_command_errors (e);
     }
   ...
 }

"call stack 2" is doomed. Probably in do_scroll_vertical () it aborts.

> 
> 
> Thanks,
> Pedro Alves
>