Re: [pm] Strange cleanups in -test8 kernel/acpi/wakeup.S

[Mika Penttilä]

Patrick Mochel wrote:

> > Some more changes landed in -test8. I have not seen them
> > before. Patrick, please, if you change something, can you post patch
> > somewhere for review before merging with Linus?
> >    
>
> Pavel, I wrote the code in the first place, before you littered your
> 'debug hacks' throughout it. I have merely been trying to simplify it for 
> debugging on other processors that are known not to work. While I 
> understand your generic plea for review, I fail to see how it would help 
> with this assembly.. 
>
>  
>
> > bkcvs info is:
> > BitKeeper to RCS/CVS export
> > ----------------------------
> > revision 1.5
> > date: 2003/10/08 22:55:45;  author: mochel;  state: Exp;  lines: +37
> > -89
> > [power] Clean up ACPI STR assembly.
> >    
>
> It might help if you read the full changeset comments. 
>
>  
>
> > diff -Nru a/arch/i386/kernel/acpi/wakeup.S
> > b/arch/i386/kernel/acpi/wakeup.S
> > --- a/arch/i386/kernel/acpi/wakeup.S    Fri Oct 17 14:43:50 2003
> > +++ b/arch/i386/kernel/acpi/wakeup.S    Fri Oct 17 14:43:50 2003
> > @@ -172,14 +172,13 @@
> > .org   0x1000
> >
> > wakeup_pmode_return:
> > -       movl    $__KERNEL_DS, %eax
> > -       movl    %eax, %ds
> > -       movw    $0x0e00 + 'u', %ds:(0xb8016)
> > -
> > -       # restore other segment registers
> > -       xorl    %eax, %eax
> > +       movw    $__KERNEL_DS, %ax
> > +       movw    %ax, %ss
> > +       movw    %ax, %ds
> > +       movw    %ax, %es
> >        movw    %ax, %fs
> >        movw    %ax, %gs
> > +       movw    $0x0e00 + 'u', 0xb8016
> >
> >        # reload the gdt, as we need the full 32 bit address
> >        lgdt    saved_gdt
> > 	~~~~~~~~~~~~~~~~~
> >
> > Notice lgdt here. You have moved setup of segment registers before
> > loading gdt. This is actually okay, if you can be sure that all such
> > registers are in gdt (and not in ldt, for example).
> >    
>
> All segments are in the GDT, as we use the same GDT in real mode as we do 
> in protected mode. However, you must reload the GDT in protected mode 
> because the GDTR is only 24 bits in real mode, but 32 in protected mode. 
>
>  
To be exact, GDTR is always 48 bits in x86. Reloading it twice seems 
pretty pointless.

--Mika




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