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

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On 04/26/2017 02:24 PM, hpa@zytor.com 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".

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[PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication Matthias Kaehlcke <mka@chromium.org> - 2017-04-26 23:00 +0200
  Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication hpa@zytor.com - 2017-04-26 23:10 +0200
    Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication Greg Hackmann <ghackmann@google.com> - 2017-04-26 23:30 +0200
      Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication "H. Peter Anvin" <hpa@zytor.com> - 2017-04-29 23:40 +0200
    Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication Kees Cook <keescook@chromium.org> - 2017-04-26 23:30 +0200
      Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication hpa@zytor.com - 2017-04-26 23:40 +0200
  Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication Kees Cook <keescook@chromium.org> - 2017-04-27 00:10 +0200

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