Doubt using "set" command with registers

[joaoandreferro@sapo.pt]

Citando Pedro Alves <palves@redhat.com>:

> On 10/31/2014 11:21 AM, joaoandreferro@sapo.pt wrote:
>> Citando Pedro Alves <palves@redhat.com>:
>
>>> I'd guess that it's kgdb itself that is blocking those writes.
>>>
>>> Try "set debug remote 1" before the "set $foo = " command.
>
>> Thanks for your answer. I turned "set debug remote 1" on again, and
>> strangely, the output tells me that "set-register" is not supported,
>> but only when I'm able to change the register value (see the output
>> below). First, I've tried with a register which I can successfully
>> change the value, and then with another one where I wasn't able to do
>> it in the past. Do you know why this behaviour occurs? Meanwhile, I'll
>> ask the same in the KGDB mailing list. Like I've mentioned, output
>> below:
>>
>> (gdb) info reg $es
>> es             0x7b	123
>> (gdb) set $es = 0x7c
>> Sending packet: $Pd=7c000000#ab...Ack
>> Packet received:
>> Packet P (set-register) is NOT supported
>
> If the P packet (write one register) is not supported, then ...
>
>> Sending packet:
>> $G14000000ccb59cc00000000067000000089fcbf10c9fcbf1ac309dc00000000079154ac09600000060000000680000007b009dc07c000000ffff0000ffff0000#61...Ack
>> Packet received: OK
>
> ... GDB tries the G packet (writes the whole set of registers in one block),
> and doesn't try P again.  That's normal.
>
>> Sending packet: $g#67...Ack
>> Packet received:
>> 14000000ccb59cc00000000067000000089fcbf10c9fcbf1ac309dc00000000079154ac09600000060000000680000007b009dc07c000000ffff0000ffff0000
>> (gdb) info reg $es
>> es             0x7c	124
>> (gdb) info reg $ss
>> ss             0x68	104
>> (gdb) set $ss = 0x69
>> Sending packet:
>> $G14000000ccb59cc00000000067000000089fcbf10c9fcbf1ac309dc00000000079154ac09600000060000000690000007b009dc07c000000ffff0000ffff0000#62...Ack
>> Packet received: OK
>
> Here GDB went straight to the G packet, because it now knows P is
> not supported.  The target accepted the write ...
>
>> Sending packet: $g#67...Ack
>> Packet received:
>> 14000000ccb59cc00000000067000000089fcbf10c9fcbf1ac309dc00000000079154ac09600000060000000680000007b009dc07c000000ffff0000ffff0000
>> (gdb) info reg $ss
>> ss             0x68	104
>
> ... but didn't make it really effective.
> Note the "68" in the g packet (read registers) reply -- seems like kgdb is
> simply ignoring the change to $ss.
>
> Thanks,
> Pedro Alves

Ok Pedro, thanks for the explanations. As I've said before, I'll try  
to obtain support on the KGDB mailing list.

Best regards,
João