Re: Exposing host debug capabilities to userspace

["Alex Bennée" <alex.bennee@linaro.org>]

Christoffer Dall <christoffer.dall@linaro.org> writes:

> On Thu, Nov 20, 2014 at 04:55:14PM +0000, Alex Bennée wrote:
>> Hi,
>> 
>> I've almost finished the ARMv8 guest debug support but I have one
>> problem left to solve. userspace needs to know how many hardware debug
>> registers are available for GDB to use.
>> * KVM ioctl KVM_GET_DEBUGREGS
>> 
>> This is currently x86 only and looks like it's more aimed at debug
>> registers than capability stuff. Also I'm not sure what the state of
>> this ioctl is compared to KVM_SET_GUEST_DEBUG. Do these APIs overlap or
>> is one an older deprecated x86 only API?
>
> The API text and a brief glance of the x86 code seems to indicate that
> this is also the vcpu state...

Yeah I was getting confused as to the difference between the two API
calls. Is this just an x86 version of what GET/SET_ONE_REG replaced?

>> * Add another KVM ioctl?
>> 
>> This would have the downside of being specific to KVM and of course
>> proliferating the API space again.
>> 
> This may not be that bad, for example, could we ever imaging that we'd
> only want to export a few of the debug registers for host gdbstub
> usage?

However it is general information which might be useful to the whole
system (although I suspect KVM and PTRACE are the only two). It would be
a shame to have an informational API wrapped up in the extra
boiler-plate of a specific API.

-- 
Alex Bennée