Re: [Qemu-arm] about armv8's prefetch decode

[Ori Chalak (A)]

Hi Peter,

Indeed, prefetch instruction affects only the micro architecture, and hence not 
needed for running correctly the generated code.
However, we developed a performance simulator for a detailed ARMv8 CPU model, 
and use Qemu to resolve the functionality.
And for this purpose we need to translate all instructions that may affect the 
pipeline behavior, caches, etc.

This is not the major usage of Qemu, however there may be others doing this and 
it may help them.
http://www.linux-kvm.org/images/4/45/01x09-Christopher_Covington-Using_Upstream_QEMU_for_CASS.pdf


Regards,

Ori Chalak

-----Original Message-----
From: Peter Maydell [mailto:address@hidden 
Sent: Thursday, March 23, 2017 7:05 PM
To: Wangjintang
Cc: qemu-arm; Shlomo Pongratz (A); Ori Chalak (A)
Subject: Re: [Qemu-arm] about armv8's prefetch decode

On 20 March 2017 at 06:35, Wangjintang <address@hidden> wrote:
>         We see that armv8's prefetch instruction decode have been 
> skipped in qemu. For some user, they need prefetch instruction, for 
> example, they use qemu to generate the instruction trace.
> We want to merge this patch to community, it's ok or not?  Thanks.

It would be helpful if you could be more precise about what is missing and what 
goes wrong (eg which instructions we mishandle). In general I believe that we 
do correctly handle the various prefetch instructions. They don't need to 
generate any intermediate code, of course, because prefetch is just a hint. 
It's possible we got the decode wrong for some subset of them.

thanks
-- PMM