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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