Re: Breakpoint commands in MI mode and "backtrace"

Simon Marchi
2017-10-09T12:02:29Z

On 2017-10-09 03:52 AM, Eli Zaretskii wrote:
>> Date: Mon, 09 Oct 2017 10:27:15 +0300
>> From: Eli Zaretskii <eliz@gnu.org>
>> CC: gdb@sourceware.org
>>
>>> Cc: gdb@sourceware.org
>>> From: Simon Marchi <simark@simark.ca>
>>> Date: Mon, 9 Oct 2017 00:16:28 -0400
>>>
>>> Hmm, strange. It is a quite complex function being executed in the hookpost-backtrace.
>>> Do you have any idea what line generates the error? It would be nice to have a
>>> reproducer without having to build emacs...
>>
>> It's this line in xgetsysm:
>>
>> set $ptr = ((struct Lisp_Symbol *) ((char *)lispsym + $ptr))
>>
>> where $ptr is a pointer to a Lisp_Symbol object:
>>
>> (gdb) p $ptr
>> $2 = (struct Lisp_Symbol *) 0x17c9e38 <dumped_data+267384>
>>
>> and lispsym is an array:
>>
>> (gdb) ptype lispsym
>> type = struct {
>> struct Lisp_Symbol s;
>> } [1298]
>>
>> Let me know if I can provide more information about this.
>
> Btw, with the patch, I get the same error if I invoke GDB in CLI mode.
>
> Thanks.
>

It's true that my patch seems to change how exceptions are handled, since
safe_execute_command catches and prints exceptions. However, that expression
does indeed seem erroenous, and I'm surprised GDB doesn't complain about it
currently. How can you add a char* and a listp_Symbol*?

Anyhow, can you try this patch here? It changes the uiout manually instead of
going through safe_execute_command.

diff --git a/gdb/cli/cli-script.c b/gdb/cli/cli-script.c
index f1db954a69..b08954132b 100644
--- a/gdb/cli/cli-script.c
+++ b/gdb/cli/cli-script.c
@@ -472,6 +472,8 @@ print_command_trace (const char *cmd)
printf_filtered ("%s\n", cmd);
}

+static void restore_interp (void *arg);
+
enum command_control_type
execute_control_command (struct command_line *cmd)
{
@@ -491,8 +493,17 @@ execute_control_command (struct command_line *cmd)
{
/* A simple command, execute it and return. */
std::string new_line = insert_user_defined_cmd_args (cmd->line);
+
+ struct interp *old_interp = interp_set_temp (INTERP_CONSOLE);
+ struct cleanup *old_chain = make_cleanup (restore_interp, old_interp);
+ scoped_restore save_uiout
+ = make_scoped_restore (&current_uiout,
+ current_interpreter ()->interp_ui_out ());
+
execute_command (&new_line[0], 0);
ret = cmd->control_type;
+
+ do_cleanups (old_chain);
break;
}