Re: [PATCH 09/13] qapi: transform target specific 'if' in runtime checks

[Markus Armbruster <armbru@redhat.com>]

Pierrick Bouvier <pierrick.bouvier@linaro.org> writes:

> On 5/9/25 11:57 PM, Markus Armbruster wrote:
>>> The build system would need generate an input document for the
>>> QAPI visitor that defines whether each constant is set to true
>>> or false, based on suitable CONFIG/TARGET conditions from meson.
>> 
>> I think the conditions that are evaluated at build time in handwritten C
>> code (with #if) should also be evaluated at build time in generated C
>> code.
>> 
>> Certain conditions are evaluated at build time in target-specific code,
>> and at runtime in target-independent code.  Again, I think handwritten
>> and generated code should work the same way.
>> 
>> Thus, to eliminate target-specific QAPI-generated code, we either
>> evaluate them at runtime, or simply eliminate them.  Elsewhere, we've
>> come to the conclusion (I think) that the latter should do at least for
>> now, likely forever, so we should try that first.
>>
>
> I'm not sure if you mean you'd prefer to eradicate #if completely.

I do not!

> We have to keep in mind that some config host #if have to stay there, or 
> they expose things that the rest of QEMU code is not supposed to see 
> (hidden under those same CONFIG_ ifdef also).

Letting people configure their QEMU build is useful and must stay.

We provide this via conditional compilation, of complete source files
(done in meson), as well as within source files (#if in C and 'if' in
QAPI).

> So we would need both if and runtime_if.

I don't understand the need for runtime_if.  Can you give an example?

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