On 01/31/2014 08:09 AM, Lluís Vilanova wrote:
> Adds the base ability to specify which events in the "trace-events" file may
> be
> used to trace guest activity in the TCG code (using the "tcg" event propery).
>
> Such events generate an extra set of tracing functions that can be called
> during
> TCG code generation and will automatically redirect a call to the appropriate
> backend-dependent tracing functions when the guest code is executed.
>
> Files generating guest code (TCG) must include "trace-tcg.h". Files declaring
> per-target helpers ("${target}/helper.h") must include
> "trace/generated-helpers.h".
>
> The flow of the generated routines is:
>
>
> [At translation time]
>
> * trace_${name}_tcg(bool, TCGv)
> Declared: "trace/generated-tcg-tracers.h"
> Defined : "trace/generated-tcg-tracers.h"
>
> * gen_helper_trace_${name}_tcg(bool, TCGv)
> Declared: "trace/generated-helpers.h"
> Defined : "trace/generated-helpers.h"
>
> Automatically transforms all the arguments and allocates them into the
> appropriate TCG temporary values (which are also freed). Provides a more
> streamlined interface by allowing events in "trace-events" to take a mix of
> tracing-supported types and TCG types.
>
> * gen_helper_trace_${name}_tcg_proxy(TCGi32, TCGv)
> Declared: "trace/generated-helpers.h"
> Defined : "trace/generated-helpers.h" (using helper machinery)
>
> The actual TCG helper function, created using QEMU's TCG helper machinery.
I suppose I have no major objection to the feature, although frankly it's
not especially exciting. I can't really imagine ever wanting to bulk trace
all of the helpers. Tracing specific helpers on a target-by-target basis,
sure. But that can be done just as easily as adding tracing code to any
other bit of C.
If I read these patches right -- and since they're mostly python I'm not
sure that I am -- we go through 5 layers of wrappers to get to the current
trace_foo expansion. Where trace_foo contains the check to see whether the
tracepoint is actually enabled.
I would strongly suggest this is backward. One should perform the check for
the tracepoint being enabled at translation time before emitting the call to
the helper in the first place.
r~
