Re: [RFC PATCH] qapi: Incorrect attempt to fix building with MC146818RTC=n

[Markus Armbruster <armbru@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 13/01/20 15:01, Markus Armbruster wrote:
>> Philippe Mathieu-Daudé <philmd@redhat.com> writes:
>> 
>>> When configured with --without-default-devices and setting
>>> MC146818RTC=n, the build fails:
>>>
>>>     LINK    x86_64-softmmu/qemu-system-x86_64
>>>   /usr/bin/ld: qapi/qapi-commands-misc-target.o: in function `qmp_marshal_rtc_reset_reinjection':
>>>   qapi/qapi-commands-misc-target.c:46: undefined reference to `qmp_rtc_reset_reinjection'
>>>   /usr/bin/ld: qapi/qapi-commands-misc-target.c:46: undefined reference to `qmp_rtc_reset_reinjection'
>>>   collect2: error: ld returned 1 exit status
>>>   make[1]: *** [Makefile:206: qemu-system-x86_64] Error 1
>>>   make: *** [Makefile:483: x86_64-softmmu/all] Error 2
>>>
>>> This patch tries to fix this, but this is incorrect because QAPI
>>> scripts only provide TARGET definitions, so with MC146818RTC=y we
>>> get:
>>>
>>>   hw/rtc/mc146818rtc.c:113:6: error: no previous prototype for ‘qmp_rtc_reset_reinjection’ [-Werror=missing-prototypes]
>>>     113 | void qmp_rtc_reset_reinjection(Error **errp)
>>>         |      ^~~~~~~~~~~~~~~~~~~~~~~~~
>>>   cc1: all warnings being treated as errors
>>>   make[1]: *** [rules.mak:69: hw/rtc/mc146818rtc.o] Error 1
>>>
>>> Any idea? :)
>>>
>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>> ---
>>>  qapi/misc-target.json | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/qapi/misc-target.json b/qapi/misc-target.json
>>> index a00fd821eb..8e49c113d1 100644
>>> --- a/qapi/misc-target.json
>>> +++ b/qapi/misc-target.json
>>> @@ -41,7 +41,7 @@
>>>  #
>>>  ##
>>>  { 'command': 'rtc-reset-reinjection',
>>> -  'if': 'defined(TARGET_I386)' }
>>> +  'if': 'defined(TARGET_I386) && defined(CONFIG_MC146818RTC)' }
>>>  
>>>  
>>>  ##
>> 
>> The generated qapi-commands-misc-target.h duly has
>> 
>>     #if defined(TARGET_I386) && defined(CONFIG_MC146818RTC)
>>     void qmp_rtc_reset_reinjection(Error **errp);
>>     void qmp_marshal_rtc_reset_reinjection(QDict *args, QObject **ret, Error **errp);
>>     #endif /* defined(TARGET_I386) && defined(CONFIG_MC146818RTC) */
>> 
>> mc146818rtc.c includes it.  But since it doesn't include
>> config-devices.h, CONFIG_MC146818RTC remains undefined, and the
>> prototype gets suppressed.
>> 
>> Crude fix: make mc146818rtc.c #include "config-devices.h".
>
> Can we modify the code generator to leave out the #if from the header,
> and only include it in the .c file?  An extra prototype is harmless.

Is *everything* we generate into headers just as harmless?

Another idea: provide a hook to make the generator insert the #include
necessary to get the macros used in 'if'.

Yet another idea: include it always in target-specific code, just like
config-target.h.