[Qemu-devel] Re: [PATCH 4/4] require #define NEED_GLOBAL_ENV for files that need the global register variable

[Paolo Bonzini <pbonzini@redhat.com>]

On 06/29/2010 05:28 PM, Paul Brook wrote:
>> On 06/29/2010 03:51 PM, Paolo Bonzini wrote:
>>> On 06/29/2010 01:30 PM, Paul Brook wrote:
>>>> I don't understand what this is supposed to achieve. The inclusion
>>>> of exec.h is what defines whether this global variable is
>>>> available. Just as importantly, it also prevents code clobbering
>>>> this value. Having one without the other makes no sense.
>>>>
>>>> Making "env" available without including exec.h would be a
>>>> different problem, but we never do that and would probably indicate
>>>> we're doing something else wrong.
>>>
>>> Paul, I agree but I was told to do something different.
>>
>> BTW, this may be useful for one thing: being able to include exec.h
>> without bringing in the global variable.
>
> I'd argue that's not a desirable feature. I'd much rather have exec.h be the
> controlling factor than have all files include the same set of headers and
> have semantics determined by some combination of preprocessor macros.
>
> I realise we already have this with NEED_CPU_H, however I don't think that's a
> precedent we want to encourage.
>
>> I didn't really see a use right now for that, but cpu_get_tb_cpu_state
>> could be something that may belong in target-*/exec.h more than in
>> target-*/cpu.h (no, I'm not going to move it); yet it cannot be moved
>> right now because it is called in exec.c.
>
> How is putting it in exec.h better?

I see cpu.h as holding things related to the CPU as a hardware device, 
and exec.h as holding things related to emulation of the CPU.

In theory, a hypothetical KVM-only/no-TCG version of QEMU would not need 
to include neither exec-all.h nor target-*/exec.h.

Paolo