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Re: [Qemu-devel] when does a target frontend need to use gen_io_start()/

From: Richard Henderson
Subject: Re: [Qemu-devel] when does a target frontend need to use gen_io_start()/gen_io_end() ?
Date: Tue, 12 May 2015 08:43:32 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05/12/2015 08:32 AM, Peter Maydell wrote:
> In order for -icount to work, it's important for the target
> translate.c code to correctly bracket any generated code which
> can "do I/O" with gen_io_start()/gen_io_end() calls. But
> does anybody know exactly what the criteria are here for this?
> It would be nice if we could document this in a comment in
> gen_icount.h -- I'm happy to write one up if somebody will just
> tell me what the right answer is :-)

I'm really not sure.

So far I've assumed "i/o"-like insns, and those that can read some sort of
cycle counter.  So while that handles easy cases like "inb" and "rdcc", it
certainly doesn't handle any target for which all i/o is memory mapped.

Which is sorta most of them these days, so the utility seems to be low...


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