Re: [Qemu-devel] [PATCH 4/7] tcg: Add support for "inlining" regions of code

[Richard Henderson]

On 09/14/2017 08:20 AM, Lluís Vilanova wrote:
> Richard Henderson writes:
> 
>> On 09/10/2017 09:27 AM, Lluís Vilanova wrote:
>>> TCG BBLs and instructions have multiple exit points from where to raise
>>> tracing events, but some of the necessary information in the generic
>>> disassembly infrastructure is not available until after generating these
>>> exit points.
>>>
>>> This patch adds support for "inline points" (where the tracing code will
>>> be placed), and "inline regions" (which identify the TCG code that must
>>> be inlined). The TCG compiler will basically copy each inline region to
>>> any inline points that reference it.
> 
>> I am not keen on this.
> 
>> Is there a reason you can't just emit the tracing code at the appropriate 
>> place
>> to begin with?  Perhaps I have to wait to see how this is used...
> 
> As I tried to briefly explain on next patch, the main problem without inlining
> is that we will see guest_tb_after_trans twice on the trace for each TB in
> conditional instructions on the guest, since they have two exit points (which 
> we
> capture when emitting goto_tb in TCG).

Without seeing the code, I suspect this is because you didn't examine the
argument to tcg_gen_exit_tb.  You can tell when goto_tb must have been emitted
and avoid logging twice.


r~