Messages in this thread | | | Date | Thu, 28 Oct 1999 13:53:20 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] Removes x86 warning messages |
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"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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