[lldb-dev] gdb-remote incompatibility with gdbserver?

[Pedro Alves via lldb-dev]

On 12/05/2017 09:50 PM, Greg Clayton via lldb-dev wrote:
> 
>> On Dec 5, 2017, at 12:45 PM, Pedro Alves <palves at redhat.com> wrote:
>>
>> On 12/05/2017 06:49 PM, Greg Clayton via lldb-dev wrote:
>>
>>> Though it does seem to be a bug that the "gdbserver" you were using doesn't support the Target XML packets that the GDB remote protocol defines? Is this some old version of GDB remote from many many years ago? Seems any recent gdbserver should have this feature?
>>
>> The x86 port of gdbserver won't send back a XML target description
>> unless the client includes "xmlRegisters=i386" in the initial
>> qSupported negotiation.  (This was done at the same time support
>> for x86 XML descriptions was added in order to keep new-gdbserver
>> working against old-gdb, because the XML register layout doesn't match
>> the no-XML layout.)
> 
> Interesting! So would we add xmlRegisters=i386 to qSupported for i386 and xmlRegisters=x86_64 for x86_64? We should have LLDB send this down to the server then and everything would just work?

It's "xmlRegisters=i386" for both 32-bit/64-bit.

I don't know whether that's all you're missing.

I should qualify "doesn't send back" better.  To be more accurate,
without "xmlRegisters=i386" gdbserver still reports back a XML description in
response to "qXfer:features:read:target.xml".  But, that description matches the
register file/layout that predated x86 XML target descriptions.  GDB still connects
and debugs fine in that case (just tried it on x86_64), but the problem will be
that that description (and the resulting g/G packet layout) doesn't include all
the new registers that have been added over the years (SSE, etc.).

So sounds like there may be more to it.

Pedro Alves