Re: [Qemu-devel] [PATCH v5 00/22] instrument: Add basic event instrumentation

[Peter Maydell <peter.maydell@linaro.org>]

On 12 September 2017 at 22:01, Lluís Vilanova <vilanova@ac.upc.edu> wrote:
> This series adds an API to add instrumentation events.
>
> It also provides additional APIs for:
> * Controlling tracing events.
> * Peek/poke guest memory.

> Future APIs (for later series):
> * Peek/poke guest registers.
> * Add breakpoints to trigger instrumentation functions.
> * Trigger instrumentation functions from guest code (former hypertrace).
> * Add events for guest code translation/execution (once the respective tracing
>   events are accepted upstream).
> * Add events for exceptions/syscalls.
> * Add events for TB invalidation (necessary for libraries to deallocate any data
>   they might have allocated for the TBs they instrumented).
>
> The instrumentation code is dynamically loaded as a library into QEMU either
> when it starts or later using its remote control interfaces. The loaded code
> only has access to function explicitly exported through the QI_VPUBLIC macro.
>
> This series is branch 'devel-instrument' in
> https://code.gso.ac.upc.edu/git/qemu-dbi.

To parallel the comment I sent on Emilio's series: I think the
first thing we should do here is work out the API we want to
present to the instrumentation plugin, because that's permanent
and we want to get it right. Then we can figure out the
implementation details later.

Particular notes:
 * putting things in the instrumentation plugin API that basically
   parallel some existing trace points is something I'm wary of,
   because a lot of our existing tracing is "output something at
   a point and in a way that's convenient for our internal
   implementation", rather than "what is the right clean interface
   to provide this sort of information". I'd rather we started
   with a blank piece of paper and designed an API, and then
   implemented it.
 * I definitely don't think we should expose to the instrumentation
   the distinction between translate time and execute time

thanks
-- PMM