[Qemu-devel] log every write to register

[Qemu-devel] log every write to register

[Sergey Smolov]

Hello, List!

I have a collection of ARMv8 register names. I need to add special 
logging mode to QEMU so that every time it is enabled, every write 
access to any of the specified registers will produce a new record to 
log, including register name and a value to be written.

Is it possible to accomplish such a task? If yes, where shall I find 
functions that implement "writing to register" functionality?

Thanks in advance!

Sincerely yours,
Sergey Smolov

Re: [Qemu-devel] log every write to register

[Peter Maydell]

On 3 November 2015 at 13:17, Sergey Smolov <smolov@ispras.ru> wrote:
> I have a collection of ARMv8 register names. I need to add special logging
> mode to QEMU so that every time it is enabled, every write access to any of
> the specified registers will produce a new record to log, including register
> name and a value to be written.
>
> Is it possible to accomplish such a task? If yes, where shall I find
> functions that implement "writing to register" functionality?

This is difficult, because we don't have a single convenient
location which all register accesses go through. (General purpose
registers and some system registers will be optimised so that
accesses are made directly from JIT generated code.)

thanks
-- PMM

Re: [Qemu-devel] log every write to register

[Peter Crosthwaite]

On Tue, Nov 3, 2015 at 8:14 AM, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 3 November 2015 at 13:17, Sergey Smolov <smolov@ispras.ru> wrote:
>> I have a collection of ARMv8 register names. I need to add special logging
>> mode to QEMU so that every time it is enabled, every write access to any of
>> the specified registers will produce a new record to log, including register
>> name and a value to be written.
>>
>> Is it possible to accomplish such a task? If yes, where shall I find
>> functions that implement "writing to register" functionality?
>
> This is difficult, because we don't have a single convenient
> location which all register accesses go through. (General purpose
> registers and some system registers will be optimised so that
> accesses are made directly from JIT generated code.)
>

You may be able to hack the TCG generation functions to call out to
helper context (which implements your log) on each op that updates
your specific regs. It will kill performance though if those registers
are hot.

Regards,
Peter

> thanks
> -- PMM
>

Re: [Qemu-devel] log every write to register

[Sergey Smolov]

03.11.2015 20:29, Peter Crosthwaite пишет:
> On Tue, Nov 3, 2015 at 8:14 AM, Peter Maydell <peter.maydell@linaro.org> wrote:
>> On 3 November 2015 at 13:17, Sergey Smolov <smolov@ispras.ru> wrote:
>>> I have a collection of ARMv8 register names. I need to add special logging
>>> mode to QEMU so that every time it is enabled, every write access to any of
>>> the specified registers will produce a new record to log, including register
>>> name and a value to be written.
>>>
>>> Is it possible to accomplish such a task? If yes, where shall I find
>>> functions that implement "writing to register" functionality?
>> This is difficult, because we don't have a single convenient
>> location which all register accesses go through. (General purpose
>> registers and some system registers will be optimised so that
>> accesses are made directly from JIT generated code.)
>>
> You may be able to hack the TCG generation functions to call out to
> helper context (which implements your log) on each op that updates
> your specific regs. It will kill performance though if those registers
> are hot.

Thank you for your answer!
Could you explain the idea in a more detailed way?
Which TCG generation functions should i hack for write-to-specific-regs 
logging?

Thanks in advance,
Sergey Smolov

Re: [Qemu-devel] log every write to register

[Sergey Fedorov]

On 17.11.2015 16:12, Sergey Smolov wrote:
>
> 03.11.2015 20:29, Peter Crosthwaite пишет:
>> On Tue, Nov 3, 2015 at 8:14 AM, Peter Maydell
>> <peter.maydell@linaro.org> wrote:
>>> On 3 November 2015 at 13:17, Sergey Smolov <smolov@ispras.ru> wrote:
>>>> I have a collection of ARMv8 register names. I need to add special
>>>> logging
>>>> mode to QEMU so that every time it is enabled, every write access
>>>> to any of
>>>> the specified registers will produce a new record to log, including
>>>> register
>>>> name and a value to be written.
>>>>
>>>> Is it possible to accomplish such a task? If yes, where shall I find
>>>> functions that implement "writing to register" functionality?
>>> This is difficult, because we don't have a single convenient
>>> location which all register accesses go through. (General purpose
>>> registers and some system registers will be optimised so that
>>> accesses are made directly from JIT generated code.)
>>>
>> You may be able to hack the TCG generation functions to call out to
>> helper context (which implements your log) on each op that updates
>> your specific regs. It will kill performance though if those registers
>> are hot.
>
> Thank you for your answer!
> Could you explain the idea in a more detailed way?
> Which TCG generation functions should i hack for
> write-to-specific-regs logging?

As of general system/coprocessor registers you could first look at
target-arm/translate-a64.c:handle_sys() and
target-arm/translate.c:disas_coproc_insn().

Best regards,
Sergey