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/* drivemap_int13h.S - interrupt handler for the BIOS drive remapper */
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2008, 2009 Free Software Foundation, Inc.
*
* GRUB 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 3 of the License, or
* (at your option) any later version.
*
* GRUB 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 GRUB. If not, see <http://www.gnu.org/licenses/>.
*/
#include <grub/symbol.h>
#define INT13H_OFFSET(x) ((x) - LOCAL (base))
.code16
/* Copy starts here. When deployed, this code must be segment-aligned. */
/* The replacement int13 handler. Preserve all registers. */
FUNCTION(grub_drivemap_handler)
LOCAL (base):
/* Save %dx for future restore. */
push %dx
/* Push flags. Used to simulate interrupt with original flags. */
pushf
/* Map the drive number (always in DL). */
push %ax
push %bx
#ifdef __APPLE__
LOCAL(mapstart_offset) = INT13H_OFFSET(LOCAL (mapstart))
movw $LOCAL(mapstart_offset), %bx
#else
movw $INT13H_OFFSET(LOCAL (mapstart)), %bx
#endif
more_remaining:
movw %cs:(%bx), %ax
cmpb %ah, %al
jz not_found /* DRV=DST => map end - drive not remapped, keep DL. */
inc %bx
inc %bx
cmpb %dl, %al
jnz more_remaining /* Not found, but more remaining, loop. */
movb %ah, %dl /* Found - drive remapped, modify DL. */
not_found:
pop %bx
pop %ax
/* If the call isn't ah=0x8 or ah=0x15 we must restore %dx. */
cmpb $0x8, %ah
jz norestore
cmpb $0x15, %ah
jz norestore
/* Restore flags. */
popf
pushf
#ifdef __APPLE__
LOCAL(oldhandler_offset) = INT13H_OFFSET (LOCAL (oldhandler))
lcall *%cs:LOCAL(oldhandler_offset)
#else
lcall *%cs:INT13H_OFFSET (LOCAL (oldhandler))
#endif
push %bp
mov %sp, %bp
tail:
/* Save new flags below %esp so the caller will recieve new flags. */
pushf
pop %dx
mov %dx, 8(%bp)
pop %bp
/* Restore %dx. */
pop %dx
iret
norestore:
/* Restore flags. */
popf
pushf
#ifdef __APPLE__
lcall *%cs:LOCAL(oldhandler_offset)
#else
lcall *%cs:INT13H_OFFSET (LOCAL (oldhandler))
#endif
push %bp
mov %sp, %bp
/* Save %dx. So it won't be restored to original value. */
mov %dx, 2(%bp)
jmp tail
/* Far pointer to the old handler. Stored as a CS:IP in the style of real-mode
IVT entries (thus PI:SC in mem). */
VARIABLE(grub_drivemap_oldhandler)
LOCAL (oldhandler):
.word 0x0, 0x0
/* This label MUST be at the end of the copied block, since the installer code
reserves additional space for mappings at runtime and copies them over it. */
.align 2
VARIABLE(grub_drivemap_mapstart)
LOCAL (mapstart):
.byte 0
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