Minor tweaks to the resume code. Previous commit reverted alignment back

to 4.  There is no need to be more strict at assembly time since we copy
the code anyway to a private page.

* Clear the direction flag and eflags.  Probably not necessary but it won't
  hurt to be safe.
* Add prefixes to all instructions to prevent any assembler mistakes.
* Remove zeroing of eax - edi.  We use those registers immediately after
  to transfer values to protected mode so this was pointless.
* Update comments to reflect info found during code review.

1 files changed, 50 insertions, 41 deletions

diff --git a/sys/i386/acpica/acpi_wakecode.S b/sys/i386/acpica/acpi_wakecode.S
index e8033e8..889a58a 100644
--- a/sys/i386/acpica/acpi_wakecode.S
+++ b/sys/i386/acpica/acpi_wakecode.S
@@ -34,20 +34,30 @@
 
 #include "assym.s"
 
+/*
+ * Resume entry point.  The BIOS enters here in real mode after POST with
+ * CS set to the page where we stored this code.  It should configure the
+ * segment registers with a flat 4 GB address space and EFLAGS.IF = 0.
+ * Depending on the previous sleep state, we may need to initialize more
+ * of the system (i.e., S3 suspend-to-RAM vs. S4 suspend-to-disk).
+ */
 	.align 4
 	.code16
 wakeup_16:
 	nop
 	cli
+	cld
 
 	/*
-	 * Set up segment registers for real mode and a small stack for
-	 * any calls we make.
+	 * Set up segment registers for real mode, a small stack for
+	 * any calls we make, and clear any flags.
 	 */
 	movw	%cs,%ax
 	movw	%ax,%ds
 	movw	%ax,%ss
 	movw	$PAGE_SIZE,%sp
+	pushl	$0
+	popfl
 
 	/* To debug resume hangs, beep the speaker if the user requested. */
 	cmpl	$1,resume_beep
@@ -75,22 +85,22 @@ nobeep:
 	movw	%ax,%ss
 nobiosreset:
 
-	/* Load GDT for real mode */
-	lgdt	physical_gdt
+	/* Load GDT for real mode.  Use 32 bit prefix for addresses >16 MB. */
+	lgdtl	physical_gdt
 
 	/* Restore CR2, CR3 and CR4 */
-	mov	previous_cr2,%eax
-	mov	%eax,%cr2
-	mov	previous_cr3,%eax
-	mov	%eax,%cr3
-	mov	previous_cr4,%eax
-	mov	%eax,%cr4
-
-	/* Transfer some values to protected mode */
+	movl	previous_cr2,%eax
+	movl	%eax,%cr2
+	movl	previous_cr3,%eax
+	movl	%eax,%cr3
+	movl	previous_cr4,%eax
+	movl	%eax,%cr4
+
+	/* Transfer some values to protected mode with an inline stack */
 #define NVALUES	9
 #define TRANSFER_STACK32(val, idx)	\
-	mov	val,%eax;		\
-	mov	%eax,wakeup_32stack+(idx+1)+(idx*4);
+	movl	val,%eax;		\
+	movl	%eax,wakeup_32stack+(idx+1)+(idx*4)
 
 	TRANSFER_STACK32(previous_ss,		(NVALUES - 9))
 	TRANSFER_STACK32(previous_fs,		(NVALUES - 8))
@@ -106,21 +116,20 @@ nobiosreset:
 	mov	physical_esp,%esi	/* to be used in 32bit code */
 
 	/* Enable protected mode */
-	mov	%cr0,%eax
+	movl	%cr0,%eax
 	orl	$(CR0_PE),%eax
-	mov	%eax,%cr0
+	movl	%eax,%cr0
 
 wakeup_sw32:
 	/* Switch to protected mode by intersegmental jump */
 	ljmpl	$KCSEL,$0x12345678	/* Code location, to be replaced */
 
-	.code32
-wakeup_32:
 	/*
-	 * Switched to protected mode w/o paging
-	 *	%esi:	KERNEL stack pointer (physical address)
+	 * Now switched to protected mode without paging enabled.
+	 *	%esi: KERNEL stack pointer (physical address)
 	 */
-
+	.code32
+wakeup_32:
 	nop
 
 	/* Set up segment registers for protected mode */
@@ -134,13 +143,13 @@ wakeup_32:
 	movl	%esi,%esp		/* physical address stack pointer */
 
 wakeup_32stack:
-	/* Operands are overwritten in 16bit code */
+	/* Operands are overwritten in 16 bit code by TRANSFER_STACK32 macro */
 	pushl	$0xabcdef09		/* ss + dummy */
 	pushl	$0xabcdef08		/* fs + gs */
 	pushl	$0xabcdef07		/* ds + es */
 	pushl	$0xabcdef06		/* gdt:base (physical address) */
-	pushl	$0xabcdef05		/* recover address */ 
-	pushl	$0xabcdef04		/* idt:base */ 
+	pushl	$0xabcdef05		/* recover address */
+	pushl	$0xabcdef04		/* idt:base */
 	pushl	$0xabcdef03		/* ldt + idt:limit */
 	pushl	$0xabcdef02		/* gdt:base */
 	pushl	$0xabcdef01		/* TR + gdt:limit */
@@ -169,15 +178,10 @@ wakeup_32stack:
 	andb	$TSS_TYPEFIX_MASK,5(%eax)
 
 	/* Prepare to return to sleep/wakeup code point */
-	lgdt	PREVIOUS_GDT
-	lidt	PREVIOUS_IDT
-
-	xorl	%eax,%eax
-	movl	%eax,%ebx
-	movl	%eax,%ecx
-	movl	%eax,%edx
-	movl	%eax,%esi
-	movl	%eax,%edi
+	lgdtl	PREVIOUS_GDT
+	lidtl	PREVIOUS_IDT
+
+	/* Pack values from the GDT to be loaded into segment registers. */
 	movl	PREVIOUS_DS,%ebx
 	movl	PREVIOUS_FS,%ecx
 	movl	PREVIOUS_SS,%edx
@@ -194,15 +198,17 @@ wakeup_32stack:
 	jmp	1f
 1:	jmp	1f
 1:
+
 	/*
-	 * Now that we are in kernel virtual memory addressing
-	 *	%ebx:	ds + es
-	 *	%ecx:	fs + gs
-	 *	%edx:	ss + dummy
-	 *	%esi:	LDTR + TR
-	 *	%edi:	recover address
+	 * Now we are in kernel virtual memory addressing with the following
+	 * original register values:
+	 *	%ebx: ds + es
+	 *	%ecx: fs + gs
+	 *	%edx: ss + dummy
+	 *	%esi: LDTR + TR
+	 *	%edi: recover address
+	 * We'll load these back into the segment registers now.
 	 */
-
 	nop
 
 	movl	%esi,%eax		/* LDTR + TR */
@@ -235,7 +241,10 @@ previous_cr4:		.long 0
 resume_beep:		.long 0
 reset_video:		.long 0
 
-/* transfer from real mode to protected mode */
+/*
+ * Transfer from real mode to protected mode.  The order of these variables
+ * is very important, DO NOT INSERT OR CHANGE unless you know why.
+ */
 previous_cr0:		.long 0
 previous_tr:		.word 0
 previous_gdt:		.word 0