Re: [PATCH] Fix -var-update for registers in frames 1 and up

[Andrew Burgess <andrew dot burgess at embecosm dot com>]

* Andrew Burgess <andrew.burgess@embecosm.com> [2016-06-08 14:00:51 +0100]:

> * Don Breazeal <donb@codesourcery.com> [2016-06-07 14:36:57 -0700]:
> 
> > This patch fixes a problem with using the MI -var-update command
> > to access the values of registers in frames other than the current
> > frame.  The patch includes a test that demonstrates the problem:
> > 
> > * run so there are several frames on the stack
> > * create a varobj for $pc in each frame, #'s 1 and above
> > * step one instruction, to modify the value of $pc
> > * call -var-update for each of the previously created varobjs
> >   to verify that they are not reported as having changed.
> > 
> > Without the patch, the -var-update command reported that $pc for all
> > frames 1 and above had changed to the value of $pc in frame 0.
> > 
> > The -var-create command takes a '--frame' argument and uses that
> > to select the frame for retrieving the register value.  But -var-update
> > has no such argument, and previously didn't do anything to select the
> > frame, so for frames other than frame 0 it returned the value of the
> > register for frame 0, instead of reporting the value as unchanged.
> 
> This shouldn't need special handling for register varobj values, if I
> create a varobj watching value 'foo' in frame 1, but have a local
> 'foo' in frame 0, a change in frame 0 'foo' will not trigger a change
> for frame 1's 'foo' varobj.
> 
> The magic is actually in varobj.c:check_scope, which makes use of the
> varobj->root->frame to select the right frame based on the type of the
> varobj, this is setup at varobj creation time.
> 
> The problem, is that for register expressions the varobj->root->frame
> is not set correctly.  This frame tracking is done using the global
> 'innermost_block' which is set in the various parser files (for
> example c-exp.y), however, this is not set for register expressions.
> I think that we probably should be doing this in
> write_dollar_variable.

Something like the following (untested):

diff --git a/gdb/parse.c b/gdb/parse.c
index 2b00708..224c022 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -705,6 +705,10 @@ handle_register:
   str.ptr++;
   write_exp_string (ps, str);
   write_exp_elt_opcode (ps, OP_REGISTER);
+  if (innermost_block == NULL
+      || contained_in (expression_context_block,
+		       innermost_block))
+    innermost_block = expression_context_block;
   return;
 }

Thanks,
Andrew