Code for actual protected-mode entry

This is the code which actually does the switch to protected mode,
including all preparation.  It is also responsible for invoking the
boot loader hooks, if present.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 54 insertions, 0 deletions

diff --git a/arch/i386/boot/pmjump.S b/arch/i386/boot/pmjump.S
new file mode 100644
index 00000000000..2e559233725
--- /dev/null
+++ b/arch/i386/boot/pmjump.S
@@ -0,0 +1,54 @@
+/* ----------------------------------------------------------------------- *
+ *
+ *   Copyright (C) 1991, 1992 Linus Torvalds
+ *   Copyright 2007 rPath, Inc. - All Rights Reserved
+ *
+ *   This file is part of the Linux kernel, and is made available under
+ *   the terms of the GNU General Public License version 2.
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * arch/i386/boot/pmjump.S
+ *
+ * The actual transition into protected mode
+ */
+
+#include <asm/boot.h>
+#include <asm/segment.h>
+
+	.text
+
+	.globl	protected_mode_jump
+	.type	protected_mode_jump, @function
+
+	.code16
+
+/*
+ * void protected_mode_jump(u32 entrypoint, u32 bootparams);
+ */
+protected_mode_jump:
+	xorl	%ebx, %ebx		# Flag to indicate this is a boot
+	movl	%edx, %esi		# Pointer to boot_params table
+	movl	%eax, 2f		# Patch ljmpl instruction
+	jmp	1f			# Short jump to flush instruction q.
+
+1:
+	movw	$__BOOT_DS, %cx
+
+	movl	%cr0, %edx
+	orb	$1, %dl			# Protected mode (PE) bit
+	movl	%edx, %cr0
+
+	movw	%cx, %ds
+	movw	%cx, %es
+	movw	%cx, %fs
+	movw	%cx, %gs
+	movw	%cx, %ss
+
+	# Jump to the 32-bit entrypoint
+	.byte	0x66, 0xea		# ljmpl opcode
+2:	.long	0			# offset
+	.word	__BOOT_CS		# segment
+
+	.size	protected_mode_jump, .-protected_mode_jump