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

Frederic Weisbecker
2010-01-26T02:22:18Z

On Tue, Jan 26, 2010 at 03:18:48AM +0100, Frederic Weisbecker wrote:
> 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)

Should be typeof(*var)

>
> #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)))
>