2019-03-06 19:44:47 +03:00
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/*
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* x86_64 boot and support code
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*
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* Copyright 2019 Linaro
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*
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* This work is licensed under the terms of the GNU GPL, version 3 or later.
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* See the COPYING file in the top-level directory.
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*
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* Unlike the i386 version we instead use Xen's PVHVM booting header
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* which should drop us automatically into 32 bit mode ready to go. I've
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* nabbed bits of the Linux kernel setup to achieve this.
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*
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* SPDX-License-Identifier: GPL-3.0-or-later
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*/
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.section .head
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#define ELFNOTE_START(name, type, flags) \
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.pushsection .note.name, flags,@note ; \
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.balign 4 ; \
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.long 2f - 1f /* namesz */ ; \
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.long 4484f - 3f /* descsz */ ; \
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.long type ; \
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1:.asciz #name ; \
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2:.balign 4 ; \
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3:
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#define ELFNOTE_END \
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4484:.balign 4 ; \
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.popsection ;
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#define ELFNOTE(name, type, desc) \
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ELFNOTE_START(name, type, "") \
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desc ; \
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ELFNOTE_END
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#define XEN_ELFNOTE_ENTRY 1
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#define XEN_ELFNOTE_HYPERCALL_PAGE 2
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#define XEN_ELFNOTE_VIRT_BASE 3
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#define XEN_ELFNOTE_PADDR_OFFSET 4
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#define XEN_ELFNOTE_PHYS32_ENTRY 18
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#define __ASM_FORM(x) x
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2020-04-03 22:11:41 +03:00
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#define __ASM_SEL(a,b) __ASM_FORM(b)
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2019-03-06 19:44:47 +03:00
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#define _ASM_PTR __ASM_SEL(.long, .quad)
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ELFNOTE(Xen, XEN_ELFNOTE_VIRT_BASE, _ASM_PTR 0x100000)
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ELFNOTE(Xen, XEN_ELFNOTE_ENTRY, _ASM_PTR _start)
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ELFNOTE(Xen, XEN_ELFNOTE_PHYS32_ENTRY, _ASM_PTR _start) /* entry == virtbase */
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ELFNOTE(Xen, XEN_ELFNOTE_PADDR_OFFSET, _ASM_PTR 0)
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/*
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* Entry point for PVH guests.
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*
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* Xen ABI specifies the following register state when we come here:
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*
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* - `ebx`: contains the physical memory address where the loader has placed
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* the boot start info structure.
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* - `cr0`: bit 0 (PE) must be set. All the other writeable bits are cleared.
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* - `cr4`: all bits are cleared.
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* - `cs `: must be a 32-bit read/execute code segment with a base of ‘0’
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* and a limit of ‘0xFFFFFFFF’. The selector value is unspecified.
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* - `ds`, `es`: must be a 32-bit read/write data segment with a base of
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* ‘0’ and a limit of ‘0xFFFFFFFF’. The selector values are all
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* unspecified.
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* - `tr`: must be a 32-bit TSS (active) with a base of '0' and a limit
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* of '0x67'.
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* - `eflags`: bit 17 (VM) must be cleared. Bit 9 (IF) must be cleared.
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* Bit 8 (TF) must be cleared. Other bits are all unspecified.
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*
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* All other processor registers and flag bits are unspecified. The OS is in
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* charge of setting up it's own stack, GDT and IDT.
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*/
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.code32
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.section .text
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.global _start
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_start:
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cld
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lgdt gdtr
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ljmp $0x8,$.Lloadcs
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.Lloadcs:
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mov $0x10,%eax
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mov %eax,%ds
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mov %eax,%es
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mov %eax,%fs
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mov %eax,%gs
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mov %eax,%ss
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/* Enable PAE mode (bit 5). */
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mov %cr4, %eax
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btsl $5, %eax
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mov %eax, %cr4
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#define MSR_EFER 0xc0000080 /* extended feature register */
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/* Enable Long mode. */
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mov $MSR_EFER, %ecx
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rdmsr
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btsl $8, %eax
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wrmsr
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/* Enable paging */
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mov $.Lpml4, %ecx
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mov %ecx, %cr3
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mov %cr0, %eax
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btsl $31, %eax
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mov %eax, %cr0
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/* Jump to 64-bit mode. */
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lgdt gdtr64
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ljmp $0x8,$.Lenter64
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.code64
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.section .text
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.Lenter64:
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// Setup stack ASAP
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movq $stack_end,%rsp
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/* don't worry about stack frame, assume everthing is garbage when we return */
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call main
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/* output any non-zero result in eax to isa-debug-exit device */
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test %al, %al
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jz 1f
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out %ax, $0xf4
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1: /* QEMU ACPI poweroff */
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mov $0x604,%edx
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mov $0x2000,%eax
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out %ax,%dx
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hlt
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jmp 1b
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/*
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* Helper Functions
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*
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* x86_64 calling convention is rdi, rsi, rdx, rcx, r8, r9
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*/
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/* Output a single character to serial port */
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.global __sys_outc
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__sys_outc:
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pushq %rax
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mov %rax, %rdx
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out %al,$0xE9
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popq %rax
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ret
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/* Interrupt Descriptor Table */
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.section .data
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.align 16
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idt_00: .int 0, 0
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idt_01: .int 0, 0
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idt_02: .int 0, 0
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idt_03: .int 0, 0
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idt_04: .int 0, 0
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idt_05: .int 0, 0
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idt_06: .int 0, 0 /* intr_6_opcode, Invalid Opcode */
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idt_07: .int 0, 0
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idt_08: .int 0, 0
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idt_09: .int 0, 0
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idt_0A: .int 0, 0
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idt_0B: .int 0, 0
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idt_0C: .int 0, 0
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idt_0D: .int 0, 0
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idt_0E: .int 0, 0
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idt_0F: .int 0, 0
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idt_10: .int 0, 0
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idt_11: .int 0, 0
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idt_12: .int 0, 0
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idt_13: .int 0, 0
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idt_14: .int 0, 0
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idt_15: .int 0, 0
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idt_16: .int 0, 0
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idt_17: .int 0, 0
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idt_18: .int 0, 0
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idt_19: .int 0, 0
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idt_1A: .int 0, 0
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idt_1B: .int 0, 0
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idt_1C: .int 0, 0
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idt_1D: .int 0, 0
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idt_1E: .int 0, 0
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idt_1F: .int 0, 0
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/*
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* Global Descriptor Table (GDT)
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*
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* This describes various memory areas (segments) through
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* segment descriptors. In 32 bit mode each segment each
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* segement is associated with segment registers which are
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* implicitly (or explicitly) referenced depending on the
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* instruction. However in 64 bit mode selectors are flat and
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* segmented addressing isn't used.
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*/
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gdt:
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.short 0
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gdtr:
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.short gdt_en - gdt - 1
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.int gdt
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// Code cs:
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.short 0xFFFF
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.short 0
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.byte 0
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.byte 0x9b
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.byte 0xCF
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.byte 0
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// Data ds:, ss:, es:, fs:, and gs:
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.short 0xFFFF
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.short 0
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.byte 0
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.byte 0x93
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.byte 0xCF
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.byte 0
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gdt_en:
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gdt64:
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.short 0
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gdtr64:
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.short gdt64_en - gdt64 - 1
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.int gdt64
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// Code
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.short 0xFFFF
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.short 0
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.byte 0
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.byte 0x9b
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.byte 0xAF
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.byte 0
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// Data
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.short 0xFFFF
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.short 0
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.byte 0
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.byte 0x93
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.byte 0xCF
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.byte 0
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gdt64_en:
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.section .bss
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.align 16
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stack: .space 65536
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stack_end:
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.section .data
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.align 4096
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.Lpd:
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i = 0
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.rept 512 * 4
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.quad 0x1e7 | (i << 21)
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i = i + 1
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.endr
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.align 4096
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.Lpdp:
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.quad .Lpd + 7 + 0 * 4096 /* 0-1 GB */
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.quad .Lpd + 7 + 1 * 4096 /* 1-2 GB */
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.quad .Lpd + 7 + 2 * 4096 /* 2-3 GB */
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.quad .Lpd + 7 + 3 * 4096 /* 3-4 GB */
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.align 4096
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.Lpml4:
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.quad .Lpdp + 7 /* 0-512 GB */
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