Re: [PATCH 0/5] x86/cpu: Introduce <asm/cpuid/types.h> and <asm/cpuid/api.h> and clean them up

[Ingo Molnar]

* H. Peter Anvin <hpa@xxxxxxxxx> wrote:

> It would be nice to get rid of the bleacherous use of *eax and *ecx 
> as input-output operands. The use of four separate pointers is just 
> barely tolerable because the compiler can remove them when the asm is 
> inlined.

So we have a nice structure of:

 struct cpuid_regs {
         u32 eax;
         u32 ebx;
         u32 ecx;
         u32 edx;
 };

So instead of:

 static inline void cpuid_count(unsigned int op, int count,
                               unsigned int *eax, unsigned int *ebx,
                               unsigned int *ecx, unsigned int *edx)

... we could have:

 static inline void cpuid_count(unsigned int op, int count, struct cpuid_regs *cregs)

or so?

plus we could implement the main CPUID call as:

 static inline void native_cpuid(struct cpuid_regs *cregs)
 {
        /* ecx is often an input as well as an output. */
        asm volatile("cpuid"
            : "=a" (cregs->eax),
              "=b" (cregs->ebx),
              "=c" (cregs->ecx),
              "=d" (cregs->edx)
            : "0" (cregs->eax), "2" (cregs->ecx)
            : "memory");
 }

and thus we give the asm() statement only a single pointer in essence, 
'cregs'?

Or do you mean something else?

Thanks,

	Ingo