Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication

[Greg Hackmann]

On 04/26/2017 02:24 PM, hpa@xxxxxxxxx wrote:
> > > This really feels like a "fix your compiler" issue.
> >
> > We already use the other forms, what's so bad about adding mul too?
> > And if this lets us build under clang, all the better.
> >
> > -Kees
>
> It's not bad per se, but if this doesn't eventually gets fixed in clang we'll have no end of this crap.

AIUI the "problem" is that clang is spilling mix_const into memory 
rather than assigning it to a register.  This is perfectly legal since 
mix_const has a constraint of "rm".  But mul needs a suffix when the 
input is a memory location, since it can't infer the multiplication 
width from the input operand anymore.

You get the same error message with gcc if you force it to use a memory 
location, by narrowing the constraint from "rm" to "m".