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From: Jun Koi <junkoi2004@gmail.com>
Date: Fri, 11 Dec 2009 17:40:23 +0900
Message-ID: <fdaac4d50912110040k339abd7dq2c08c179869ba426@mail.gmail.com>
Subject: Re: [Qemu-devel] TCG is hard to understand!
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To: Laurent Desnogues <laurent.desnogues@gmail.com>
Cc: Alexander Graf <agraf@suse.de>, qemu-devel@nongnu.org

On Fri, Dec 11, 2009 at 4:36 PM, Laurent Desnogues
<laurent.desnogues@gmail.com> wrote:
> On Fri, Dec 11, 2009 at 4:18 AM, Jun Koi <junkoi2004@gmail.com> wrote:
>>
>> Another question: I look at tcg_gen_callN() to see how the helper is
>> executed. We put the helper opcode into the TCG code buffer, and put
>> helper's params into gen_opparam_buf.
>>
>> However, then when TCG generates code to actually call the helper, we
>> just put the opcode of the host insn into the output buffer, which is
>> target code at this step, then run it.
>>
>> Now when the helper is executed, it must get its param from the stack,
>> which is really the host stack. But as said above, its params are in
>> gen_opparam_buf, but not in stack?
>> I searched around, and dont see anywhere we link gen_opparam_buf with
>> the host stack. So how the helper can get its param??
>>
>> Surely I missed something, or misunderstand the whole picture. Any hint?
>
> Take a look at tcg.c:tcg_reg_alloc_call
>

Now I see how TCG manipulates the stack memory there.

Thanks,
J