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

[Richard Henderson <rth@twiddle.net>]

On 05/06/2015 08:44 AM, Peter Maydell wrote:
> On 6 May 2015 at 15:12, Richard Henderson <rth@twiddle.net> 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.


r~