diff options
Diffstat (limited to 'purgatory/arch/i386/compat_x86_64.S')
| -rw-r--r-- | purgatory/arch/i386/compat_x86_64.S | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/purgatory/arch/i386/compat_x86_64.S b/purgatory/arch/i386/compat_x86_64.S new file mode 100644 index 0000000..1649085 --- /dev/null +++ b/purgatory/arch/i386/compat_x86_64.S @@ -0,0 +1,100 @@ +/* + * kexec: Linux boots Linux + * + * Copyright (C) 2003,2004,2005 Eric Biederman (ebiederm@xmission.com) + * + * 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 (version 2 of the License). + * + * 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., 675 Mass Ave, Cambridge, MA 02139, USA. + */ + + .equ MSR_K6_EFER, 0xC0000080 + .equ EFER_LME, 0x00000100 + .equ X86_CR4_PAE, 0x00000020 + .equ CR0_PG, 0x80000000 + + .globl compat_x86_64, compat_x86_64_entry32 + .text + .code64 + .balign 16 +compat_x86_64: + /* Setup a temporary gdt */ + /* This also acts as a serializing instruction ensuring + * my self modifying code works. + */ + lgdt gdt(%rip) + + /* Switch to 32bit compatiblity mode */ + ljmp *lm_exit_addr(%rip) +lm_exit: + .code32 + + /* Disable paging */ + movl %cr0, %eax + andl $~CR0_PG, %eax + movl %eax, %cr0 + + /* Disable long mode */ + movl $MSR_K6_EFER, %ecx + rdmsr + andl $~EFER_LME, %eax + wrmsr + + /* Disable PAE */ + xorl %eax, %eax + movl %eax, %cr4 + + /* load the data segments */ + movl $0x18, %eax /* data segment */ + movl %eax, %ds + movl %eax, %es + movl %eax, %ss + movl %eax, %fs + movl %eax, %gs + + /* set all of the registers to known values */ + /* leave %esp alone */ + + xorl %eax, %eax + xorl %ebx, %ebx + xorl %ecx, %ecx + xorl %edx, %edx + xorl %esi, %esi + xorl %edi, %edi + xorl %ebp, %ebp + + jmp *compat_x86_64_entry32 + + .section ".rodata" + .balign 16 +gdt: /* 0x00 unusable segment + * 0x08 unused + * so use them as the gdt ptr + */ + .word gdt_end - gdt - 1 + # A quad word pointer to the gdt with the high 32bits 0 + .long gdt, 0 + .word 0, 0, 0 + + /* 0x10 4GB flat code segment */ + .word 0xFFFF, 0x0000, 0x9A00, 0x00CF + /* 0x18 4GB flat data segment */ + .word 0xFFFF, 0x0000, 0x9200, 0x00CF +gdt_end: + +lm_exit_addr: + .long lm_exit + .long 0x10 + +compat_x86_64_entry32: + .long 0 +.size compat_x86_64_entry32, . - compat_x86_64_entry32 |