Re: [PATCH 7/8] percpu: add __percpu sparse annotations to hw_breakpoint

Frederic Weisbecker
2010-01-26T02:18:54Z

On Tue, Jan 26, 2010 at 11:13:59AM +0900, Tejun Heo wrote:
> Hello,
>
> On 01/26/2010 11:01 AM, Frederic Weisbecker wrote:
> > So, may be it considers you are applying the address space overriding
> > to the pointer to the type and not to the type itself.
> >
> > Consider:
> >
> > int __percpu i;
> >
> > What you do above *might* be considered as if SHIFT_PERCPU_PTR
> > returns something of a type:
> >
> > int * __percpu i;
> >
> > So the pointer is in the normal address space, but its content is in
> > __percpu address space.
> >
> > What if you do this:
> >
> >
> > #define SHIFT_PERCPU_PTR(__p, __offset) ({ \
> > __verify_pcpu_ptr((__p)); \
> > RELOC_HIDE((__p), (__offset)); \
> > })
> >
> > #define per_cpu(var, cpu) \
> > (typeof(var) __kernel __force)(*SHIFT_PERCPU_PTR(&(var), per_cpu_offset(cpu)))
>
> arch/x86/kernel/cpu/common.c:1149:20: warning: cast to non-scalar
> arch/x86/kernel/cpu/common.c:1149:20: error: strange non-value function or array
> CC arch/x86/kernel/cpu/common.o
> arch/x86/kernel/cpu/common.c: In function 'cpu_init':
> arch/x86/kernel/cpu/common.c:1149: error: cast specifies array type
>
> Can't cast that way. :-(

What about this? It doesn't use direct cast to scalar but should
create a pointer type to kernel space datas:

#define kernel_space_t(var) \
(typeof(var) __kernel __force)

#define SHIFT_PERCPU_PTR(__p, __offset) ({ \
__verify_pcpu_ptr((__p)); \
RELOC_HIDE((typeof(*(kernel_space_t(var)) __kernel __force *)(__p), (__offset)); \
})

#define per_cpu(var, cpu) \
(*SHIFT_PERCPU_PTR(&(var), per_cpu_offset(cpu)))