Commit 7052fdd8 authored by H. Peter Anvin's avatar H. Peter Anvin Committed by Linus Torvalds
Browse files

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: default avatarH. Peter Anvin <hpa@zytor.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5e8ddcbe
/* -*- 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
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