Re: [PATCH] APM support doesn't compile with binutils 2.8.1.0.24
H. J. Lu (hjl@freya.yggdrasil.com)
Wed, 25 Mar 1998 10:51:38 -0800 (PST)
>
>
>
> On Wed, 25 Mar 1998, Bernhard Rosenkraenzer wrote:
> >
> > According to the binutils people, it's related to bogus asm in apm_bios.c
> > - the patch I've attached fixes it.
>
> Are the binutils people aware that the size prefix _does_ make a
> difference for segment loads?
>
> If you do a 16-bit "mov seg -> reg", the operation will write only the low
> 16 bits, while if you do a 32-bit version it will actually write all 32
> bits (high bits zero, I do believe).
>
> (Just to confuse matters: if the destination is memory, it seems to be
> always written 16 bits at a time regardless of the size of the operand.
> Don't you all love Intel?)
>
> Anyway, this does mean that people can quite _deliberately_ need both the
> 16- and 32-bit versions, and gas _should_ accept a "w" or "l" at the
> instruction to imply which one is needed.
>
> The old gas bug was that it defaulted to 16-bit mode which is slower and
> bigger (and is also strange, considering that gas always otherwise
> defaults to 32-bit mode when not told otherwise). But the new gas
> behaviour is equally buggy in that it appears to not support the 16-bit
> mode at all, and even complains when explicitly given a (legal) size.
>
> The "b" case (8-bit) is illegal and should not be allowed (which was my
> original complaint about the patch that Ingo posted).
>
> In short:
>
> push %ds : legal, should default to 32-bit mode, no override
> pushl %ds : legal, 32-bit, no override
> pushw %ds : legal, 16-bit, operand size override
> pushb %ds : illegal
>
> mov %ds,%eax : legal, should default to 32-bit mode, no override
> mov %ds,%ax : if gas notices that "%ax" is 16-bit it would be great.
> movw %ds,%ax : 16-bit, operand size override REQUIRED
> movl %ds,%eax : 32-bit, no override
>
There are no pushw/pushb for cs/ds/es/fs/gs/ss in my Intel reference
manual. You can only use push %ds or pop %ds. I will fix mov in
binutils 2.8.1.0.26.
H.J.
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