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Diffstat (limited to 'arch/x86/lib/traveler.S')
| -rw-r--r-- | arch/x86/lib/traveler.S | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/arch/x86/lib/traveler.S b/arch/x86/lib/traveler.S new file mode 100644 index 0000000000..2b6dc85ed2 --- /dev/null +++ b/arch/x86/lib/traveler.S @@ -0,0 +1,183 @@ +/* + * Copyright (C) 2009 Juergen Beisert, Pengutronix + * + * Mostly stolen from the GRUB2 project + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License as + * published by the Free Software Foundation; either version 2 of + * the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, + * MA 02111-1307 USA + * + */ + +/** + * @file + * @brief Switch from the flat mode world into the real mode world and vice versa + * + * Note: These functions are *called* and return in a different operating mode + */ + +/** + * @fn void real_to_prot(void) + * @brief Switch from temp. real mode back to flat mode + * + * Called from a 32 bit flat mode segment and returns into a 16 bit segment + */ + +/** + * @fn void prot_to_real(void) + * @brief Switch from flat mode to real mode + * + * Called from a 16 bit real mode segment and returns into a 32 bit segment + */ + +#ifndef DOXYGEN_SHOULD_SKIP_THIS + +#include <asm/modes.h> + + .file "walkyrie.S" + +/* keep the current flat mode stack pointer, while playing in real mode */ + .section .boot.data.protstack + .code32 +protstack: .long 4 +/* temp. store */ +return_addr: .long 4 + + + .section .boot.text.real_to_prot, "ax" + .code16 + .globl real_to_prot + .type real_to_prot, @function + +/* Note: This routine should not change any other standard registers than eax */ +real_to_prot: + /* + * Always disable the interrupts, when returning to flat mode + */ + cli + + /* turn on protected mode */ + movl %cr0, %eax + orl $0x00000001, %eax + movl %eax, %cr0 + + /* jump to relocation, flush prefetch queue, and reload %cs */ + DATA32 ljmp $__BOOT_CS, $return_to_flatmode + +/* ----------------------------------------------------------------------- */ + .section .boot.text.return_to_flatmode, "ax" + .type return_to_flatmode, @function + .code32 + +return_to_flatmode: + /* reload other segment registers */ + movw $__BOOT_DS, %ax + movw %ax, %ds + movw %ax, %es + movw %ax, %fs + movw %ax, %gs + movw %ax, %ss + + /* move the return address from the real mode to the flat mode stack */ + movl (%esp), %eax + movl %eax, return_addr + + /* setup again the flat mode stack */ + movl protstack, %eax + movl %eax, %esp + movl %eax, %ebp + + movl return_addr, %eax + movl %eax, (%esp) + + /* flag we returned happy here */ + xorl %eax, %eax + ret + + .size real_to_prot, .-real_to_prot + +/* ------------------------------------------------------------------------ */ + +/* Note: This routine should not change any other standard registers than eax */ + + .section .boot.text.prot_to_real, "ax" + .globl prot_to_real + .type prot_to_real, @function + .extern boot_stack + .code32 + +prot_to_real: + /* save the protected mode stack */ + movl %esp, %eax + movl %eax, protstack + + /* prepare the real mode stack */ + /* - address to call to the top of this stack */ + movl (%esp), %eax + movl %eax, boot_stack - 4 + + /* - the stack itself */ + movl $boot_stack - 4, %eax + movl %eax, %esp + movl %eax, %ebp + + /* prepare segments limits to 16 bit */ + movw $__REAL_DS, %ax + movw %ax, %ds + movw %ax, %es + movw %ax, %fs + movw %ax, %gs + movw %ax, %ss + + /* at last, also limit the code segment to 16 bit */ + ljmp $__REAL_CS, $return_to_realmode + +/* ----------------------------------------------------------------------- */ + + .section .boot.text.return_to_realmode, "ax" +return_to_realmode: + .code16 + + /* disable protected mode */ + movl %cr0, %eax + andl $(~0x00000001), %eax + movl %eax, %cr0 + + /* + * all the protected mode settings are still cached in the CPU. + * Refresh them by re-loading all registers in realmode + * Start with the CS, continue with the data registers + */ + ljmp $0, $enter_realmode + +enter_realmode: + xorl %eax, %eax + movw %ax, %ds + movw %ax, %es + movw %ax, %fs + movw %ax, %gs + movw %ax, %ss + /* + * back in plain real mode now, we can play again with the BIOS + */ + + /* restore interrupts */ + sti + + /* return on realmode stack! */ + DATA32 ret + + .size prot_to_real, .-prot_to_real + +#endif |