From 8e4bff4cab0ddac6060645b0715210484d02ff40 Mon Sep 17 00:00:00 2001
From: Yuval Adam <_@yuv.al>
Date: Wed, 30 Aug 2017 08:25:59 +0000
Subject: Initial file dump from open source release

---
 arch/x86/boot/pmjump.S | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 arch/x86/boot/pmjump.S

(limited to 'arch/x86/boot/pmjump.S')

diff --git a/arch/x86/boot/pmjump.S b/arch/x86/boot/pmjump.S
new file mode 100644
index 00000000..3e0edc6d
--- /dev/null
+++ b/arch/x86/boot/pmjump.S
@@ -0,0 +1,77 @@
+/* ----------------------------------------------------------------------- *
+ *
+ *   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.
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * The actual transition into protected mode
+ */
+
+#include <asm/boot.h>
+#include <asm/processor-flags.h>
+#include <asm/segment.h>
+#include <linux/linkage.h>
+
+	.text
+	.code16
+
+/*
+ * void protected_mode_jump(u32 entrypoint, u32 bootparams);
+ */
+GLOBAL(protected_mode_jump)
+	movl	%edx, %esi		# Pointer to boot_params table
+
+	xorl	%ebx, %ebx
+	movw	%cs, %bx
+	shll	$4, %ebx
+	addl	%ebx, 2f
+	jmp	1f			# Short jump to serialize on 386/486
+1:
+
+	movw	$__BOOT_DS, %cx
+	movw	$__BOOT_TSS, %di
+
+	movl	%cr0, %edx
+	orb	$X86_CR0_PE, %dl	# Protected mode
+	movl	%edx, %cr0
+
+	# Transition to 32-bit mode
+	.byte	0x66, 0xea		# ljmpl opcode
+2:	.long	in_pm32			# offset
+	.word	__BOOT_CS		# segment
+ENDPROC(protected_mode_jump)
+
+	.code32
+	.section ".text32","ax"
+GLOBAL(in_pm32)
+	# Set up data segments for flat 32-bit mode
+	movl	%ecx, %ds
+	movl	%ecx, %es
+	movl	%ecx, %fs
+	movl	%ecx, %gs
+	movl	%ecx, %ss
+	# The 32-bit code sets up its own stack, but this way we do have
+	# a valid stack if some debugging hack wants to use it.
+	addl	%ebx, %esp
+
+	# Set up TR to make Intel VT happy
+	ltr	%di
+
+	# Clear registers to allow for future extensions to the
+	# 32-bit boot protocol
+	xorl	%ecx, %ecx
+	xorl	%edx, %edx
+	xorl	%ebx, %ebx
+	xorl	%ebp, %ebp
+	xorl	%edi, %edi
+
+	# Set up LDTR to make Intel VT happy
+	lldt	%cx
+
+	jmpl	*%eax			# Jump to the 32-bit entrypoint
+ENDPROC(in_pm32)
-- 
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