Il 17/10/2013 12:58, Gleb Natapov ha scritto:
>>> > > @@ -143,14 +143,14 @@ static inline int rtc_in(u8 reg)
>>> > > {
>>> > > u8 x = reg;
>>> > > asm volatile("outb %b1, $0x70; inb $0x71, %b0"
>>> > > - : "+a"(x) : "0"(x));
>>> > > + : "=a"(x) : "0"(x));
>>> > > return x;
>>> > > }
>> >
>> > This should be wrong. GCC should complain that the same operand is used
>> > for both input and output but has an "=" constraint.
>> >
>>> > > static inline void rtc_out(u8 reg, u8 val)
>>> > > {
>>> > > asm volatile("outb %b1, $0x70; mov %b2, %b1; outb %b1, $0x71"
>>> > > - : "+a"(reg) : "0"(reg), "ri"(val));
>>> > > + : "=a"(reg) : "0"(reg), "ri"(val));
>>> > > }
>> >
>> > Same here.
>> >
>> > But I'm not sure what is the error message for older GCC for s3.c, as I
>> > wrote in reply to Michael.
>> >
> x86/s3.c: In function 'main':
> x86/s3.c:145: error: inconsistent operand constraints in an 'asm'
>
> And I am puzzled by this too.
Hmm, looks like my version is the incorrect one and, if you use "+a" you
need not use the matching input constraint. So it's either your
version, or one that removes the "0" altogether.
Thus,
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Paolo
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