Re: [PATCH 1/3] x86, acpi: Eliminate saved_eip
From: Pavel Machek
Date: Wed Jun 17 2015 - 05:28:43 EST
On Tue 2015-06-16 14:46:20, Denys Vlasenko wrote:
> On 06/16/2015 12:05 PM, Pavel Machek wrote:
> >> diff --git a/arch/x86/kernel/acpi/wakeup_32.S b/arch/x86/kernel/acpi/wakeup_32.S
> >> index 665c6b7..eef2bd3 100644
> >> --- a/arch/x86/kernel/acpi/wakeup_32.S
> >> +++ b/arch/x86/kernel/acpi/wakeup_32.S
> >> @@ -31,17 +31,11 @@ wakeup_pmode_return:
> >> movl %cs:saved_magic, %eax
> >> cmpl $0x12345678, %eax
> >> - jne bogus_magic
> >> -
> >> - # jump to place where we left off
> >> - movl saved_eip, %eax
> >> - jmp *%eax
> >> -
> >> + je ret_point
> >> bogus_magic:
> > Longjump is supposed to flush the prefetch, but hopefully nothing
> > depends on that detail... ...
> > no.
> > https://en.wikibooks.org/wiki/X86_Assembly/Protected_Mode#Entering_Protected_Mode
> > longjump is supposed to be there. Sorry about that. I guess indirect
> > jump is not neccessary, and we should add a comment there.
> What "long jump"? It's not a far (segment:offset) jump, it's a near
> jump (one which only changes the offset), indirect one through a register.
Yup, you are right, the ljmp is few instructions above that.
> And we aren't switching to or from protected mode here.
wakeup_pmode_return... that's just after switching to protected mode
Acked-by: Pavel Machek <pavel@xxxxxx>
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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