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

[Eduardo Habkost <ehabkost@redhat.com>]

On Mon, Sep 11, 2017 at 12:23:10PM +0200, Paolo Bonzini wrote:
> 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 <david@redhat.com>
> >>>> ---
> >>>>  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?
> 
> See Markus's reply.  But, maybe it's even better to use S390CPU* and
> include target/s390x/cpu-qom.h, which by design provides as little
> definitions as needed.

I don't see an argument against moving typedef CPUS390XState to
typedefs.h in Markus' reply.  I see one argument for it (reducing
the need for non-cyclic includes).

cpu-qom.h includes cpu.h, so I don't know why using S390CPU*
would solve any problem.  I don't disagree about changing the
function to use S390CPU* eventually, but it would still require
us make a choice between: a) including the header where the
typedef name is declared (cpu.h or cpu-qom.h); or b) moving the
typedef name declaration to typedefs.h.

> 
> > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> > ---
> > 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
> > @@ -21,6 +21,7 @@ typedef struct Chardev Chardev;
> >  typedef struct CompatProperty CompatProperty;
> >  typedef struct CPUAddressSpace CPUAddressSpace;
> >  typedef struct CPUState CPUState;
> > +typedef struct CPUS390XState CPUS390XState;
> >  typedef struct DeviceListener DeviceListener;
> >  typedef struct DeviceState DeviceState;
> >  typedef struct DirtyBitmapSnapshot DirtyBitmapSnapshot;
> > diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> > index 032d1de2e8..f99a82cd5e 100644
> > --- a/target/s390x/cpu.h
> > +++ b/target/s390x/cpu.h
> > @@ -80,7 +80,7 @@ typedef struct MchkQueue {
> >      uint16_t type;
> >  } MchkQueue;
> >  
> > -typedef struct CPUS390XState {
> > +struct CPUS390XState {
> >      uint64_t regs[16];     /* GP registers */
> >      /*
> >       * The floating point registers are part of the vector registers.
> > @@ -174,7 +174,7 @@ typedef struct CPUS390XState {
> >      /* currently processed sigp order */
> >      uint8_t sigp_order;
> >  
> > -} CPUS390XState;
> > +};
> >  
> >  static inline CPU_DoubleU *get_freg(CPUS390XState *cs, int nr)
> >  {
> > 
> > 
> > 
> >> diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> >> index 3aa2e46aac..032d1de2e8 100644
> >> --- a/target/s390x/cpu.h
> >> +++ b/target/s390x/cpu.h
> >> @@ -721,6 +721,5 @@ int s390_cpu_virt_mem_rw(S390CPU *cpu, vaddr laddr,
> >> uint8_t ar, void *hostbuf,
> >>
> >>  /* outside of target/s390x/ */
> >>  S390CPU *s390_cpu_addr2state(uint16_t cpu_addr);
> >> -int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code);
> >>
> >>  #endif
> >> diff --git a/target/s390x/misc_helper.c b/target/s390x/misc_helper.c
> >> index b142db71c6..8b07535b02 100644
> >> --- a/target/s390x/misc_helper.c
> >> +++ b/target/s390x/misc_helper.c
> >> @@ -35,6 +35,7 @@
> >>  #include "sysemu/sysemu.h"
> >>  #include "hw/s390x/ebcdic.h"
> >>  #include "hw/s390x/s390-virtio-hcall.h"
> >> +#include "hw/s390x/sclp.h"
> >>  #endif
> >>
> >>  /* #define DEBUG_HELPER */
> >>
> >>
> >> Opinions?
> >>
> >>
> >>
> >> -- 
> >>
> >> Thanks,
> >>
> >> David
> > 
> 

-- 
Eduardo