Re: [RFC PATCH] configure: Poison (almost) all target-specific #defines

[Thomas Huth <thuth@redhat.com>]

On 15/03/2021 16.37, Peter Maydell wrote:
> On Mon, 15 Mar 2021 at 15:26, Thomas Huth <thuth@redhat.com> wrote:
>>
>> On 15/03/2021 15.52, Philippe Mathieu-Daudé wrote:
>>> On 3/15/21 2:54 PM, Thomas Huth wrote:
>>>> We are generating a lot of target-specific defines in the *-config-devices.h
>>>> and *-config-target.h files. Using them in common code is wrong and leads
>>>> to very subtle bugs since a "#ifdef CONFIG_SOMETHING" is not working there
>>>> as expected. To avoid these issues, we are already poisoning some of the
>>>> macros in include/exec/poison.h - but maintaining this list manually is
>>>> cumbersome. Thus let's generate the list of poisoned macros automatically
>>>> instead.
>>>> Note that CONFIG_TCG (which is also defined in config-host.h) and
>>>
>>> IIRC we can't poison CONFIG_XEN / CONFIG_HAX because they are
>>> pulled in via "sysemu/hw_accel.h".
>>
>> That's a good hint ... but I think it can be fixed with a patch like this:
>>
>> diff a/include/sysemu/hw_accel.h b/include/sysemu/hw_accel.h
>> --- a/include/sysemu/hw_accel.h
>> +++ b/include/sysemu/hw_accel.h
>> @@ -12,19 +12,24 @@
>>    #define QEMU_HW_ACCEL_H
>>
>>    #include "hw/core/cpu.h"
>> +
>> +#ifdef NEED_CPU_H
>> +
>>    #include "sysemu/hax.h"
>>    #include "sysemu/kvm.h"
>>    #include "sysemu/hvf.h"
>>    #include "sysemu/whpx.h"
> 
> This doesn't look right, because sysemu/kvm.h itself contains
> a NEED_CPU_H check, which implies that there are situations where
> NEED_CPU_H is not defined and we need to pull in the header.

I just tried, and QEMU seems to compile fine with my patch... I guess the 
check for NEED_CPU_H is mainly required for files that include 
"sysemu/kvm.h" directly, without the detour via hw_accel.h.

Anyway, I can also push the check rather into the hax.h, hvf.h and whpx.h 
files themselves, to make them more similar to kvm.h.

  Thomas