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Re: [Qemu-devel] [RFC] Tracing guest register usage
From: |
Lluís Vilanova |
Subject: |
Re: [Qemu-devel] [RFC] Tracing guest register usage |
Date: |
Wed, 05 Oct 2016 12:06:04 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
Richard Henderson writes:
> On 09/30/2016 08:13 AM, Lluís Vilanova wrote:
>>> (2) an internal state change
>>> to DisasContext, reflected in INDEX_op_insn_start, with no changes to any
>>> TCG
>>> registers. So you'll not actually be tracking eflags at all.
>>
>> I don't follow what you mean. AFAIK INDEX_op_insn_start does not change the
>> guest eflags.
> It sets cc_op, which affects how eflags is computed.
I see tcg_gen_insn_start() gets dc->cc_op as a second argument, but I really
don't see where it gets modified (I'm looking at tcg_gen_code() on the
INDEX_op_insn_start case).
If you have the time, I'd like to understand that; I'm just curious.
But regardless of this specific case, we still have all the instructions
implemented with TCG helpers, which won't have any reguster usage information. I
was pretty convinced that was enough for some basic analysis using the traces,
but I might just as well keep proper register usage on my instrumentation tree.
Thanks,
Lluis
- Re: [Qemu-devel] [RFC] Tracing guest register usage,
Lluís Vilanova <=