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Re: [Qemu-devel] [PATCH 6/7] monitor: "i": Add ARM specifics

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH 6/7] monitor: "i": Add ARM specifics
Date: Wed, 06 May 2015 11:24:15 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05/06/2015 08:44 AM, Peter Maydell wrote:
> On 6 May 2015 at 15:12, Richard Henderson <address@hidden> wrote:
>> On 05/06/2015 12:06 AM, Peter Crosthwaite wrote:
>>> Can
>>> we rely on the env/CPUState always being up to date during
>>> target_disas (which happens at translate time?) or will we need to go
>>> field by field to make sure any env updates explicitly occur before
>>> target_disas?
>> I *think* so, but it's a near thing.  The path goes
>>  tb_find_fast:
>>   cpu_get_tb_cpu_state, fill fill in flags for TB from current ENV state.
>>   tb_find_slow,
>>     tb_gen_code, using those same flags.
>> There's the edge case of re-translation, but I'm going to assert that cpu 
>> mode
>> changes ought not happen in that context.  Doing otherwise means that the
>> kernel has just switched modes, the translator has failed to end the TB, and
>> the new code has faulted immediately.
> This is making the assumption that what the disassembler sees as
> a "different mode" is the same as what the translator sees as a
> "different mode" for which it needs to end the TB... This happens
> to be true for ARM, at least, but I don't see any particular
> reason why it is necessarily so for everything.

I'm pretty sure it is, though.  Certainly true for x86 and mips.
I might call it a translator bug not to end the TB at a mode change.


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