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

[Thomas Huth]

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