Re: [kvm-devel] [PATCH] KVM: Avoid using vmx instruction directly

[Avi Kivity <avi@qumranet.com>]

Arnd Bergmann wrote:
> On Thursday 09 November 2006 12:08, Avi Kivity wrote:
>   
>> Index: linux-2.6/drivers/kvm/kvm_main.c
>> ===================================================================
>> --- linux-2.6.orig/drivers/kvm/kvm_main.c
>> +++ linux-2.6/drivers/kvm/kvm_main.c
>> @@ -369,8 +369,8 @@ static void vmcs_clear(struct vmcs *vmcs
>>         u64 phys_addr = __pa(vmcs);
>>         u8 error;
>>  
>> -       asm volatile ("vmclear %1; setna %0"
>> -                      : "=m"(error) : "m"(phys_addr) : "cc", "memory" );
>> +       asm volatile (ASM_VMX_VMCLEAR_RAX "; setna %0"
>> +                      : "=g"(error) : "a"(&phys_addr) : "cc", "memory" );
>>         if (error)
>>                 printk(KERN_ERR "kvm: vmclear fail: %p/%llx\n",
>>                        vmcs, phys_addr);
>>     
>
> I'm not an expert on inline assembly, but don't you need an extra
> '"m" (phys_addr)' to make sure that gcc actually puts the variable
> on the stack instead of passing a NULL pointer as '"a"(&phys_addr)'?
>
>   

Taking a variable's address should force its contents into memory (like 
calling an uninlined function with &var).


-- 
error compiling committee.c: too many arguments to function