diff options
Diffstat (limited to 'grub-core/lib/i386/relocator16.S')
| -rw-r--r-- | grub-core/lib/i386/relocator16.S | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/grub-core/lib/i386/relocator16.S b/grub-core/lib/i386/relocator16.S new file mode 100644 index 0000000..982415d --- /dev/null +++ b/grub-core/lib/i386/relocator16.S @@ -0,0 +1,193 @@ +/* + * GRUB -- GRand Unified Bootloader + * Copyright (C) 2009,2010 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/>. + */ + +/* The code segment of the protected mode. */ +#define CODE_SEGMENT 0x08 + +/* The data segment of the protected mode. */ +#define DATA_SEGMENT 0x10 + +#define PSEUDO_REAL_CSEG 0x18 + +#define PSEUDO_REAL_DSEG 0x20 + +#include "relocator_common.S" + + .p2align 4 /* force 16-byte alignment */ + +VARIABLE(grub_relocator16_start) + PREAMBLE + + movl %esi, %eax + movw %ax, (LOCAL (cs_base_bytes12) - LOCAL (base)) (RSI, 1) + shrl $16, %eax + movb %al, (LOCAL (cs_base_byte3) - LOCAL (base)) (RSI, 1) + + RELOAD_GDT + .code32 + /* Update other registers. */ + movl $DATA_SEGMENT, %eax + movl %eax, %ds + movl %eax, %es + movl %eax, %fs + movl %eax, %gs + movl %eax, %ss + + DISABLE_PAGING + +#ifdef __x86_64__ + /* Disable amd64. */ + movl $GRUB_MEMORY_CPU_AMD64_MSR, %ecx + rdmsr + andl $(~GRUB_MEMORY_CPU_AMD64_MSR_ON), %eax + wrmsr +#endif + + /* Turn off PAE. */ + movl %cr4, %eax + andl $(~GRUB_MEMORY_CPU_CR4_PAE_ON), %eax + movl %eax, %cr4 + + /* Update other registers. */ + movl $PSEUDO_REAL_DSEG, %eax + movl %eax, %ds + movl %eax, %es + movl %eax, %fs + movl %eax, %gs + movl %eax, %ss + + movl %esi, %eax + shrl $4, %eax + movw %ax, (LOCAL (segment) - LOCAL (base)) (%esi, 1) + + /* jump to a 16 bit segment */ + ljmp $PSEUDO_REAL_CSEG, $(LOCAL (cont2) - LOCAL(base)) +LOCAL(cont2): + .code16 + + /* clear the PE bit of CR0 */ + movl %cr0, %eax + andl $(~GRUB_MEMORY_CPU_CR0_PE_ON), %eax + movl %eax, %cr0 + + /* flush prefetch queue, reload %cs */ + /* ljmp */ + .byte 0xea + .word LOCAL(cont3)-LOCAL(base) +LOCAL(segment): + .word 0 + +LOCAL(cont3): + /* we are in real mode now + * set up the real mode segment registers : DS, SS, ES + */ + /* movw imm16, %ax. */ + .byte 0xb8 +VARIABLE(grub_relocator16_ds) + .word 0 + movw %ax, %ds + + /* movw imm16, %ax. */ + .byte 0xb8 +VARIABLE(grub_relocator16_es) + .word 0 + movw %ax, %es + + /* movw imm16, %ax. */ + .byte 0xb8 +VARIABLE(grub_relocator16_fs) + .word 0 + movw %ax, %fs + + /* movw imm16, %ax. */ + .byte 0xb8 +VARIABLE(grub_relocator16_gs) + .word 0 + movw %ax, %gs + + /* movw imm16, %ax. */ + .byte 0xb8 +VARIABLE(grub_relocator16_ss) + .word 0 + movw %ax, %ss + + /* movw imm16, %ax. */ + .byte 0xb8 +VARIABLE(grub_relocator16_sp) + .word 0 + movzwl %ax, %esp + + /* movw imm32, %edx. */ + .byte 0x66, 0xba +VARIABLE(grub_relocator16_edx) + .long 0 + + /* Cleared direction flag is of no problem with any current + payload and makes this implementation easier. */ + cld + + /* ljmp */ + .byte 0xea +VARIABLE(grub_relocator16_ip) + .word 0 +VARIABLE(grub_relocator16_cs) + .word 0 + + .code32 + + /* GDT. Copied from loader/i386/linux.c. */ + .p2align 4 +LOCAL(gdt): + .word 0, 0 + .byte 0, 0, 0, 0 + + /* -- code segment -- + * base = 0x00000000, limit = 0xFFFFF (4 KiB Granularity), present + * type = 32bit code execute/read, DPL = 0 + */ + .word 0xFFFF, 0 + .byte 0, 0x9A, 0xCF, 0 + + /* -- data segment -- + * base = 0x00000000, limit 0xFFFFF (4 KiB Granularity), present + * type = 32 bit data read/write, DPL = 0 + */ + .word 0xFFFF, 0 + .byte 0, 0x92, 0xCF, 0 + + /* -- 16 bit real mode CS -- + * base = 0x00000000, limit 0x0FFFF (1 B Granularity), present + * type = 16 bit code execute/read only/conforming, DPL = 0 + */ + .word 0xFFFF +LOCAL(cs_base_bytes12): + .word 0 +LOCAL(cs_base_byte3): + .byte 0 + + .byte 0x9E, 0, 0 + + /* -- 16 bit real mode DS -- + * base = 0x00000000, limit 0x0FFFF (1 B Granularity), present + * type = 16 bit data read/write, DPL = 0 + */ + .word 0xFFFF, 0 + .byte 0, 0x92, 0, 0 +LOCAL(gdt_end): + +VARIABLE(grub_relocator16_end) |