Re: [PATCH 3/3] gdb, gdbserver: introduce the 'x' RSP packet for binary memory read

[Tom Tromey <tom@tromey.com>]

>>>>> Aktemur, Tankut Baris <tankut.baris.aktemur@intel.com> writes:

>> I think the probing idea is that you simply try the 'x' command the
>> first time it is needed.  If remote sends an empty response (not an 'E'
>> response), then the packet isn't supported, so you disable it and retry
>> with 'm'.
>> 
>> This is documented in the Overview node:

> Yes, I get this idea, and the 'X' packet actually uses it.  My concern there is
> that (1) sending this packet with an arbitrary address and length 0 seems too
> artificial; (2) using the proposed reply format, the target would send an empty reply
> both when it does not recognize the packet and when it recognizes because the length
> argument in the probe is 0 (the same problem would exist with the 'm', 'p', 'g' packets
> if we were to probe them).  This would not be an issue if we decide to force the reply
> to always start with a marker character, as suggested in Ciaran's email.

I definitely think that gdb should not send an 'x' packet with an
arbitrary address and a length of 0.

Instead the idea is that if the packet is not explicitly forbidden
(either via a gdb command or by previous probe failure), just attempt to
use this packet for the first memory read.

If the remote reports the packet as unsupported, fall back to the 'm'
packet and carry on.

I think the docs should be explicit about what a 0-length read means.
I tend to think this should just be an error.

I also prefer Ciaran's idea for the response packet.  I didn't realize
other packets already did this or perhaps I would have suggested it.

thanks,
Tom