Re: [PATCH] Removes x86 warning messages

H. Peter Anvin (hpa@transmeta.com)
Thu, 28 Oct 1999 13:53:20 -0700


"Richard B. Johnson" wrote:
>>
> Not. Look at page 26-210, the '*'. About protected mode moves to
> segment registers, of the Intel Rag., ISBN 1-55512-159-4, Intel 486
> Programmer's reference manual. Also page 26-2, Table 26-1, Effective
> size attributes.
>
> There is no movw in Intel syntax nor is there a movl.
>
> In Intel, if the segment size (the D bit in the segment descriptor),
> is set to 32 bits, every instruction that uses 16 bit registers requires
> the address-size prefix because this is the only thing that shows
> the processor the difference.
>

In the case of segment register operations, the size of 16 bits is
implicit in the opcode, so there is never any need to generate it.
Technically you can do a movl from a 32-bit memory operand to force 32
bits of memory to be touched; otherwise they are exactly equivalent.

Therefore, the assembler should always generate the shortest form. Case
closed.

>
> I'm sure Intel would like to hear from you if you have a devised
> a better way to use their processors, or if you have discovered
> that their documentation is wrong.
>

Intel's documentation is wrong all over the place. They clearly could
care less about the correctness of their documentation. I'm not paid to
proofread their docs for them.

-hpa

-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!

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