Code for actual protected-mode entry

/* -*- linux-c -*- ------------------------------------------------------- *

 *

 *   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/pm.c

 *

 * Prepare the machine for transition to protected mode.

 */

#include "boot.h"

#include <asm/segment.h>

/*

 * Invoke the realmode switch hook if present; otherwise

 * disable all interrupts.

 */

static void realmode_switch_hook(void)

{

	if (boot_params.hdr.realmode_swtch) {

		asm volatile("lcallw *%0"

			     : : "m" (boot_params.hdr.realmode_swtch)

			     : "eax", "ebx", "ecx", "edx");

	} else {

		asm volatile("cli");

		outb(0x80, 0x70); /* Disable NMI */

		io_delay();

	}

}

/*

 * A zImage kernel is loaded at 0x10000 but wants to run at 0x1000.

 * A bzImage kernel is loaded and runs at 0x100000.

 */

static void move_kernel_around(void)

{

	/* Note: rely on the compile-time option here rather than

	   the LOADED_HIGH flag.  The Qemu kernel loader unconditionally

	   sets the loadflags to zero. */

#ifndef __BIG_KERNEL__

	u16 dst_seg, src_seg;

	u32 syssize;

	dst_seg =  0x1000 >> 4;

	src_seg = 0x10000 >> 4;

	syssize = boot_params.hdr.syssize; /* Size in 16-byte paragraphs */

	while (syssize) {

		int paras  = (syssize >= 0x1000) ? 0x1000 : syssize;

		int dwords = paras << 2;

		asm volatile("pushw %%es ; "

			     "pushw %%ds ; "

			     "movw %1,%%es ; "

			     "movw %2,%%ds ; "

			     "xorw %%di,%%di ; "

			     "xorw %%si,%%si ; "

			     "rep;movsl ; "

			     "popw %%ds ; "

			     "popw %%es"

			     : "+c" (dwords)

			     : "rm" (dst_seg), "rm" (src_seg)

			     : "esi", "edi");

		syssize -= paras;

		dst_seg += paras;

		src_seg += paras;

	}

#endif

}

/*

 * Disable all interrupts at the legacy PIC.

 */

static void mask_all_interrupts(void)

{

	outb(0xff, 0xa1);	/* Mask all interrupts on the seconday PIC */

	io_delay();

	outb(0xfb, 0x21);	/* Mask all but cascade on the primary PIC */

	io_delay();

}

/*

 * Reset IGNNE# if asserted in the FPU.

 */

static void reset_coprocessor(void)

{

	outb(0, 0xf0);

	io_delay();

	outb(0, 0xf1);

	io_delay();

}

/*

 * Set up the GDT

 */

#define GDT_ENTRY(flags,base,limit)		\

	(((u64)(base & 0xff000000) << 32) |	\

	 ((u64)flags << 40) |			\

	 ((u64)(limit & 0x00ff0000) << 32) |	\

	 ((u64)(base & 0x00ffff00) << 16) |	\

	 ((u64)(limit & 0x0000ffff)))

struct gdt_ptr {

	u16 len;

	u32 ptr;

} __attribute__((packed));

static void setup_gdt(void)

{

	/* There are machines which are known to not boot with the GDT

	   being 8-byte unaligned.  Intel recommends 16 byte alignment. */

	static const u64 boot_gdt[] __attribute__((aligned(16))) = {

		/* CS: code, read/execute, 4 GB, base 0 */

		[GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),

		/* DS: data, read/write, 4 GB, base 0 */

		[GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),

	};

	struct gdt_ptr gdt;

	gdt.len = sizeof(boot_gdt)-1;

	gdt.ptr = (u32)&boot_gdt + (ds() << 4);

	asm volatile("lgdtl %0" : : "m" (gdt));

}

/*

 * Set up the IDT

 */

static void setup_idt(void)

{

	static const struct gdt_ptr null_idt = {0, 0};

	asm volatile("lidtl %0" : : "m" (null_idt));

}

/*

 * Actual invocation sequence

 */

void go_to_protected_mode(void)

{

	/* Hook before leaving real mode, also disables interrupts */

	realmode_switch_hook();

	/* Move the kernel/setup to their final resting places */

	move_kernel_around();

	/* Enable the A20 gate */

	if (enable_a20()) {

		puts("A20 gate not responding, unable to boot...\n");

		die();

	}

	/* Reset coprocessor (IGNNE#) */

	reset_coprocessor();

	/* Mask all interrupts in the PIC */

	mask_all_interrupts();

	/* Actual transition to protected mode... */

	setup_idt();

	setup_gdt();

	protected_mode_jump(boot_params.hdr.code32_start,

			    (u32)&boot_params + (ds() << 4));

}

/* ----------------------------------------------------------------------- *

 *

 *   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