Re: [Qemu-devel] [PATCH 5/7] qapi: add query-cpudefs command

[Anthony Liguori <aliguori@us.ibm.com>]

Peter Maydell <peter.maydell@linaro.org> writes:

> On 27 July 2012 14:37, Anthony Liguori <aliguori@us.ibm.com> wrote:
>> This command attempts to map to the behavior of -cpu ?.  Unfortunately, the
>> output of this command differs wildly across targets.
>
> I've never really understood why so much of the cpu selection
> logic is deferred to target-*...

It will be fixed as part of the QOM conversion.

>> To accomodate this, we use a weak symbol to implement a default version of the
>> command that fails with a QERR_NOT_SUPPORTED error code.  Targets can then
>> override and implement this command if it makes sense for them.
>
> This is a bit of a weak reason (boom boom!) for requiring a platform
> specific thing like weak symbols, though, and it's not how we handle
> similar existing cases (eg see the configure/makefile logic for
> memory_mapping.c vs memory_mapping-stub.c).

I don't think we have a consistent approach today FWIW.  I think using
weak symbols is sufficiently compelling that it will become consistent.

>
> If having separate configure/make stuff for each of these things
> sounds a bit heavyweight, we could just have a target-stubs.c which
> #includes cpu.h and has a lot of
> #ifndef TARGET_QUERY_CPUDEFS
> [stub version]
> #endif
> #ifndef TARGET_GET_MEMORY_MAPPING
> [stub version]
> #endif

This is pretty hideous.

FWIW, weak symbols are supported on OS X as of 10.2.

Regards,

Anthony Liguori

>
> etc.
>
> -- PMM