MI and modifying register value

[Tom Tromey]

>>>>> "Jan" == Jan Vrany via Gdb <gdb@sourceware.org> writes:

Jan> 1) There's an MI command to set register value: -data-write-register-values
Jan>    This command is not documented and looking at the code, seems to be somewhat
Jan>    half-implemented - does not use <format> parameter its comment mentions and
Jan>    only works for frame 0 (but using --frame 1 does not result in an error,
Jan>    it just silently changes value in frame 0). 

Jan>    Is this command some leftover that should not be used (but kept for some
Jan>    old clients)? Or is it something to fix? 

It's very old and seems to have landed without tests or documentation.

I think the addition of 'format' here must be some kind of copy-paste
bug.  I can't imagine how it would be useful.  However, in the spirit of
API conservatism I think it should just be left untouched -- we can just
document that it's a mistake and clients can send whatever they like for
this argument.

Fixing the frame bug seems completely fine to me.

Jan> 2) Another way to change register value is CLI command `set r4 = 0x4`. There's
Jan>    no mechanism the MI client gets notified about the change - there's no =register-changed
Jan>    async event. 

Surely it must be "set $r4 = 0x4" -- the "$" should be needed I think.

Jan>    Is this by purpose? I'd expect some kind of notification, just like there's =memory-changed
Jan>    event. Also, in Python API, there's memory_ckanged event which get triggered when
Jan>    using `set` to modify register. 

There's the weird "-data-list-changed-registers" command.  It doesn't
really documented "changed since what", but it seems to be "since last
time this was called".  There's a static local variable in the
implementation :-(

I do see there is a "register_changed" observable, so implementing the
notification seems relatively easy.  This observable seems to only track
changes made by the user, though.

Tom