Re: How to Read Program Architecture from GDB/MI?

Andrew Burgess
2016-07-26T08:09:23Z

* Paramjot Oberoi <paramjot@gmail.com> [2016-07-26 02:27:31 -0400]:

> Thank you for the quick response, it got me down the right track.
> Unfortunately simply commenting out that if() won't work for me as the
> output will no longer have the GDB/MI request IDs. It would be the
> same as if I did "interpreter-exec mi "show architecture." I believe
> the correct fix will require some proper planning. I've spent a few
> hours looking at GDB's source code and I can't think of a clean way to
> implement it.
>
> The core issue is the output from "show architecture" and
> "interpreter-exec mi "-gdb-show architecture"" do not match in the
> case that the architecture is not set or is set to auto. If you
> manually set the architecture ("set architecture i386") the GDB/MI
> output is correct. As you mentioned the c->show_value_func
> (show_architecture) only gets called for the console output case, and
> not for the GDB/MI. It is the source of the difference.
>
> Console output:
> (gdb) show architecture
> The target architecture is set automatically (currently i386) --->
> set_architecture_string is NULL, but output correctly says the target
> architecture is auto, and prints out the current architecture
> (gdb) set architecture auto
> The target architecture is set automatically (currently i386)
> (gdb) show architecture
> The target architecture is set automatically (currently i386) --->
> set_architecture_string is "auto", and prints out the current
> architecture
>
> GDB/MI output:
> (gdb) interpreter-exec mi "-gdb-show architecture"
> ^done ---> set_architecture_string is NULL so nothing is output, does
> not print out the current architecture
> (gdb) set architecture auto
> The target architecture is set automatically (currently i386)
> (gdb) interpreter-exec mi "-gdb-show architecture"
> ^done,value="auto" ---> set_architecture_string is "auto", does not
> print out the current architecture
>
> c->show_value_func (show_architecture) is what handles the special
> logic for having "auto" or uninitialized architectures:
>
> static void
> show_architecture (struct ui_file *file, int from_tty,
> struct cmd_list_element *c, const char *value)
> {
> if (target_architecture_user == NULL)
> fprintf_filtered (file, _("The target architecture is set "
> "automatically (currently %s)\n"),
> gdbarch_bfd_arch_info (get_current_arch ())->printable_name);
> else
> fprintf_filtered (file, _("The target architecture is assumed to be %s\n"),
> set_architecture_string);
> }
>
> There is no such equivalent callback for the GDB/MI case. I can't
> think of a way to do this that wouldn't be hackish. One thought was to
> modify the if() else to specifically look for this case:
>
> if (ui_out_is_mi_like_p (uiout))
> {
> if(c->show_value_func == show_architecture)
> {
> // reimplement the logic of show_architecture() here, but for MI
> // we would need to wipe the existing stb because it might already
> have the word "auto" in there
>
> }
> ui_out_field_stream (uiout, "value", stb);
> }
> else
> {
> ...
> ...
> }

As you point out I don't think there's a quick fix to your problem,
and the comment in 'do_show_command' acknowledges that this area is
broken when it comes to MI.

As a quick fix how about the patch below. It's not ideal, but it
might be enough for you.

The basic idea is to wrap the MI return from -gdb-show into a tuple,
then add an extra field 'message', which contains the raw output of a
CLI 'show' command.

[ I think that long term we'd probably switch to a tuple anyway, when
we correctly handle things like a variable being 'auto' we'd
probably want a reply that looked something like: {value="auto",
current="i386"}, so switching to a tuple is probably the way to
go. ]

For now however, the display of value is not fixed, so the 'auto'
value does not get displayed at all, but you do always get the message
string, the default reply now looks like this:

(gdb) interpreter-exec mi "-gdb-show architecture"
^done,{message="The target architecture is set automatically (currently i386)\n"}

You would then have to parse the message string yourself.

Hope this helps,
Andrew

----

diff --git a/gdb/cli/cli-setshow.c b/gdb/cli/cli-setshow.c
index eb17158..f7597cf 100644
--- a/gdb/cli/cli-setshow.c
+++ b/gdb/cli/cli-setshow.c
@@ -650,7 +650,23 @@ do_show_command (const char *arg, int from_tty, struct cmd_list_element *c)
MI and CLI specific versions. */

if (ui_out_is_mi_like_p (uiout))
- ui_out_field_stream (uiout, "value", stb);
+ {
+ struct ui_file *msg_file;
+ char *value;
+
+ make_cleanup_ui_out_tuple_begin_end (uiout, NULL);
+ ui_out_field_stream (uiout, "value", stb);
+
+ value = ui_file_xstrdup (stb, NULL);
+ make_cleanup (xfree, value);
+ msg_file = mem_fileopen ();
+ if (c->show_value_func != NULL)
+ c->show_value_func (msg_file, from_tty, c, value);
+ else
+ deprecated_show_value_hack (msg_file, from_tty, c, value);
+
+ ui_out_field_stream (uiout, "message", msg_file);
+ }
else
{
char *value = ui_file_xstrdup (stb, NULL);