Re: [rft] s2ram wakeup moves to .c, could fix few machines

[H. Peter Anvin]

Rafael J. Wysocki wrote:
> On Thursday, 7 of February 2008, H. Peter Anvin wrote:
> > Rafael J. Wysocki wrote:
> > > Index: linux-2.6/arch/x86/kernel/acpi/realmode/wakeup.S
> > > ===================================================================
> > > --- /dev/null
> > > +++ linux-2.6/arch/x86/kernel/acpi/realmode/wakeup.S
> > > @@ -0,0 +1,122 @@
> > > +/*
> > > + * ACPI wakeup real mode startup stub
> > > + */
> > > +#include <asm/segment.h>
> > > +#include <asm/msr-index.h>
> > > +#include <asm/page_64.h>
> > > +#include <asm/pgtable_64.h>
> > > +
> > > +	.code16
> > > +	.section ".header", "a"
> > > +
> > > +/* This should match the structure in wakeup.h */
> > > +		.globl	wakeup_header
> > > +wakeup_header:
> > > +video_mode:	.short	0	/* Video mode number */
> > > +pmode_return:	.byte	0x66, 0xea	/* ljmpl */
> > > +		.long	0	/* offset goes here */
> > > +		.short	__KERNEL_CS
> > Missing a .short pad here... Pavel fixed that at some point, I thought.
>
> Hm, the struct in wakeup.h doesn't contain it too.  Why exactly is it
> necessary?

Err, I guess it's only necessary if _jmp2 is declared u32.  I generally 
prefer to keep fields naturally aligned even though x86 doesn't require 
it, it's a bit of paranoia on my part.

> Yeah.  Pavel, what's at 0x3f00, btw?

To be fair, this might have come from my early hack, I don't know for sure.

> In fact, I'd prefer to remove .signature from the header and use the
> end_signature only, so that I can use struct wakeup_header for addressing
> the header fields in the assembly too.

I *thought* that's what I had originally.  I'm a bit confused, or it 
might have been something Pavel changed.

> > Furthermore, by doing so, you're also padding the binary out to its maximum
> > length, so you might as well just remove the .bss-clearing stuff.
>
> Do you mean placing the header at the end will fill the area between it and the
> code with zeros, so the .bss clearing is not necessary?

Yes.  It could, of course, also be cleared by a simple memset() in the 
setup code in the kernel, as opposed by the initial assembly code. 
That's probably the preferred option.

	-hpa
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