Re: [Qemu-devel] [PATCH v3 08/21] s390x: move sclp_service_call() to sclp.h

[Thomas Huth]

On 10.09.2017 00:07, Eduardo Habkost wrote:
> On Fri, Sep 08, 2017 at 02:46:36PM +0200, David Hildenbrand wrote:
>> On 08.09.2017 06:21, Thomas Huth wrote:
>>> On 07.09.2017 22:13, David Hildenbrand wrote:
>>>> Implemented in sclp.c, so let's move it to the right include file.
>>>> Fix up one include. Do a forward declaration of CPUS390XState to fix the
>>>> two sclp consoles complaining.
>>>>
>>>> Signed-off-by: David Hildenbrand <address@hidden>
>>>> ---
>>>>  include/hw/s390x/sclp.h    | 2 ++
>>>>  target/s390x/cpu.h         | 1 -
>>>>  target/s390x/misc_helper.c | 1 +
>>>>  3 files changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/include/hw/s390x/sclp.h b/include/hw/s390x/sclp.h
>>>> index a72d096081..4b86a8a293 100644
>>>> --- a/include/hw/s390x/sclp.h
>>>> +++ b/include/hw/s390x/sclp.h
>>>> @@ -242,5 +242,7 @@ sclpMemoryHotplugDev 
>>>> *init_sclp_memory_hotplug_dev(void);
>>>>  sclpMemoryHotplugDev *get_sclp_memory_hotplug_dev(void);
>>>>  void sclp_service_interrupt(uint32_t sccb);
>>>>  void raise_irq_cpu_hotplug(void);
>>>> +typedef struct CPUS390XState CPUS390XState;
>>>> +int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code);
>>>
>>> That's dangerous and likely does not work with certain versions of GCC.
>>> You can't do a "forward declaration" with typedef in C, I'm afraid. See
>>> for example:
>>>
>>>  https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg01454.html
>>>  https://lists.gnu.org/archive/html/qemu-devel/2017-06/msg03337.html
>>>  https://stackoverflow.com/questions/8367646/redefinition-of-typedef
>>>
>>> All this typedef'ing in QEMU is pretty bad ... we run into this problem
>>> again and again. include/qemu/typedefs.h is just a work-around for this.
>>> I know people like typedefs for some reasons (I used to do that, too,
>>> before I realized the trouble with them), but IMHO we should rather
>>> adopt the typedef-related rules from the kernel coding conventions instead:
>>>
>>>  https://www.kernel.org/doc/html/v4.13/process/coding-style.html#typedefs
>>>
>>>   Thomas
>>>
>>
>> Yes, this is really nasty. And I wasn't aware of the involved issues.
>>
>> This seems to be the only feasible solution (including cpu.h sounds
>> wrong and will require a bunch of other includes):
>>
>>
>> diff --git a/include/hw/s390x/sclp.h b/include/hw/s390x/sclp.h
>> index a72d096081..ce80915a02 100644
>> --- a/include/hw/s390x/sclp.h
>> +++ b/include/hw/s390x/sclp.h
>> @@ -242,5 +242,7 @@ sclpMemoryHotplugDev
>> *init_sclp_memory_hotplug_dev(void);
>>  sclpMemoryHotplugDev *get_sclp_memory_hotplug_dev(void);
>>  void sclp_service_interrupt(uint32_t sccb);
>>  void raise_irq_cpu_hotplug(void);
>> +struct CPUS390XState;
>> +int sclp_service_call(struct CPUS390XState *env, uint64_t sccb,
>> uint32_t code);
>>
>>  #endif
> 
> Why not use typedefs.h?
> 
> Signed-off-by: Eduardo Habkost <address@hidden>
> ---
> diff --git a/include/hw/s390x/sclp.h b/include/hw/s390x/sclp.h
> index 4b86a8a293..3512bf8283 100644
> --- a/include/hw/s390x/sclp.h
> +++ b/include/hw/s390x/sclp.h
> @@ -242,7 +242,6 @@ sclpMemoryHotplugDev *init_sclp_memory_hotplug_dev(void);
>  sclpMemoryHotplugDev *get_sclp_memory_hotplug_dev(void);
>  void sclp_service_interrupt(uint32_t sccb);
>  void raise_irq_cpu_hotplug(void);
> -typedef struct CPUS390XState CPUS390XState;
>  int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code);
>  
>  #endif
> diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
> index 39bc8351a3..9c97bffa92 100644
> --- a/include/qemu/typedefs.h
> +++ b/include/qemu/typedefs.h

Using include/qemu/typedefs.h here is IMHO really ugly. Do we really
want to pollute a common include file with target specific code? My
preferences are first to avoid typdefs, but if we really need/want them
(do we? There is no comment about this in our coding styles), I think we
should rather introduce target-specific typedefs.h headers, too, for
everything that is not part of the common code.

 Thomas