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 000000000000..2e559233725a
--- /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