Logo Search packages:      
Sourcecode: linux version File versions  Download package

pm.c

/* -*- 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)
                       : "r" (dst_seg), "r" (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 secondary 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),
      };
      /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
         of the gdt_ptr contents.  Thus, make it static so it will
         stay in memory, at least long enough that we switch to the
         proper kernel GDT. */
      static 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));
}

Generated by  Doxygen 1.6.0   Back to index