Re: [Qemu-devel] [PULL v2 00/30] QAPI patches for 2018-03-01

[Peter Maydell]

On 2 March 2018 at 14:05, Eric Blake <address@hidden> wrote:
> On 03/02/2018 06:38 AM, Peter Maydell wrote:
>> This produces a huge pile of warnings from my OSX toolchain.
>>
>> When running ar on libqemuutil.a:
>>    AR      libqemuutil.a
>>
>> /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib:
>> file: libqemuutil.a(qapi-types.o) has no symbols
>
>
> Part of this change was moving the location of the generated ./qapi-types.c
> to qapi/qapi-types.c.  Could it be that you are doing an incremental build,
> rather than a clean build, and the compiler is picking up the stale version
> of the file rather than its new location?

I am doing an incremental build, yes. That needs to work, not break...

>> I had a look at the autogenerated .c files on my Linux build, and they
>> seem to consist only of a bunch of #includes. Why are we not generating
>> any code here?

> But I just checked, and at least for qapi/qapi-types.c, the generated file
> IS just a list of includes; and in fact, it looks like all of the mentioned
> files are in that boat (for example, qapi/transaction.json has no events, so
> qapi/qapi-events-transaction.c being empty makes sense).

> I know that some compilers are picky about that.

Yes, I think this is what is causing the problem.

> Is a typedef enough to
> cause the compiler to have something to compile without warnings?

Given that the warnings are coming from nm and ranlib, anything that
doesn't actually cause a symbol to be put into the .o file isn't going
to be enough I suspect.

> If so,
> does this patch solve things?  If it does, I'll squash it in the right place
> within the series and submit a v3 pull request.
>
> diff --git i/scripts/qapi/common.py w/scripts/qapi/common.py
> index 077e0fde4f4..aed32646c00 100644
> --- i/scripts/qapi/common.py
> +++ w/scripts/qapi/common.py
> @@ -2035,6 +2035,13 @@ class QAPIGenC(QAPIGen):
>  ''',
>                       blurb=self._blurb, copyright=self._copyright)
>
> +    def _bottom(self, fname):
> +        return mcgen('''
> +/* Dummy typedef to prevent empty .o file */
> +typedef int %(name)s;
> +''',
> +                     name=c_name(fname))
> +
>
>  class QAPIGenH(QAPIGenC):

I just tested this, and it isn't sufficient.

thanks
-- PMM