0ca2426bea
On x86 machines we can use an emulator to run option ROMS as with other architectures. But with some additional effort (mostly due to the 16-bit nature of option ROMs) we can run them natively. Add support for this. Signed-off-by: Simon Glass <sjg@chromium.org>
282 lines
6.0 KiB
ArmAsm
282 lines
6.0 KiB
ArmAsm
/*
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* From coreboot x86_asm.S, cleaned up substantially
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*
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* Copyright (C) 2009-2010 coresystems GmbH
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*
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* SPDX-License-Identifier: GPL-2.0
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*/
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#include <asm/processor.h>
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#include <asm/processor-flags.h>
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#include "bios.h"
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#define SEG(segment) $segment * X86_GDT_ENTRY_SIZE
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/*
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* This is the interrupt handler stub code. It gets copied to the IDT and
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* to some fixed addresses in the F segment. Before the code can used,
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* it gets patched up by the C function copying it: byte 3 (the $0 in
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* movb $0, %al) is overwritten with the interrupt numbers.
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*/
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.code16
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.globl __idt_handler
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__idt_handler:
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pushal
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movb $0, %al /* This instruction gets modified */
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ljmp $0, $__interrupt_handler_16bit
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.globl __idt_handler_size
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__idt_handler_size:
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.long . - __idt_handler
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.macro setup_registers
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/* initial register values */
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movl 44(%ebp), %eax
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movl %eax, __registers + 0 /* eax */
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movl 48(%ebp), %eax
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movl %eax, __registers + 4 /* ebx */
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movl 52(%ebp), %eax
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movl %eax, __registers + 8 /* ecx */
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movl 56(%ebp), %eax
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movl %eax, __registers + 12 /* edx */
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movl 60(%ebp), %eax
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movl %eax, __registers + 16 /* esi */
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movl 64(%ebp), %eax
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movl %eax, __registers + 20 /* edi */
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.endm
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.macro enter_real_mode
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/* Activate the right segment descriptor real mode. */
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ljmp SEG(X86_GDT_ENTRY_16BIT_CS), $PTR_TO_REAL_MODE(1f)
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1:
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.code16
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/*
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* Load the segment registers with properly configured segment
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* descriptors. They will retain these configurations (limits,
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* writability, etc.) once protected mode is turned off.
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*/
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mov SEG(X86_GDT_ENTRY_16BIT_DS), %ax
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mov %ax, %ds
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mov %ax, %es
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mov %ax, %fs
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mov %ax, %gs
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mov %ax, %ss
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/* Turn off protection */
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movl %cr0, %eax
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andl $~X86_CR0_PE, %eax
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movl %eax, %cr0
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/* Now really going into real mode */
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ljmp $0, $PTR_TO_REAL_MODE(1f)
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1:
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/*
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* Set up a stack: Put the stack at the end of page zero. That way
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* we can easily share it between real and protected, since the
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* 16-bit ESP at segment 0 will work for any case.
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*/
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mov $0x0, %ax
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mov %ax, %ss
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/* Load 16 bit IDT */
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xor %ax, %ax
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mov %ax, %ds
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lidt __realmode_idt
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.endm
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.macro prepare_for_irom
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movl $0x1000, %eax
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movl %eax, %esp
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/* Initialise registers for option rom lcall */
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movl __registers + 0, %eax
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movl __registers + 4, %ebx
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movl __registers + 8, %ecx
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movl __registers + 12, %edx
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movl __registers + 16, %esi
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movl __registers + 20, %edi
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/* Set all segments to 0x0000, ds to 0x0040 */
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push %ax
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xor %ax, %ax
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mov %ax, %es
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mov %ax, %fs
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mov %ax, %gs
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mov SEG(X86_GDT_ENTRY_16BIT_FLAT_DS), %ax
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mov %ax, %ds
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pop %ax
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.endm
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.macro enter_protected_mode
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/* Go back to protected mode */
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movl %cr0, %eax
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orl $X86_CR0_PE, %eax
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movl %eax, %cr0
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/* Now that we are in protected mode jump to a 32 bit code segment */
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data32 ljmp SEG(X86_GDT_ENTRY_32BIT_CS), $PTR_TO_REAL_MODE(1f)
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1:
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.code32
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mov SEG(X86_GDT_ENTRY_32BIT_DS), %ax
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mov %ax, %ds
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mov %ax, %es
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mov %ax, %gs
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mov %ax, %ss
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mov SEG(X86_GDT_ENTRY_32BIT_FS), %ax
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mov %ax, %fs
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/* restore proper idt */
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lidt idt_ptr
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.endm
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/*
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* In order to be independent of U-Boot's position in RAM we relocate a part
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* of the code to the first megabyte of RAM, so the CPU can use it in
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* real-mode. This code lives at asm_realmode_code.
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*/
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.globl asm_realmode_code
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asm_realmode_code:
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/* Realmode IDT pointer structure. */
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__realmode_idt = PTR_TO_REAL_MODE(.)
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.word 1023 /* 16 bit limit */
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.long 0 /* 24 bit base */
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.word 0
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/* Preserve old stack */
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__stack = PTR_TO_REAL_MODE(.)
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.long 0
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/* Register store for realmode_call and realmode_interrupt */
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__registers = PTR_TO_REAL_MODE(.)
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.long 0 /* 0 - EAX */
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.long 0 /* 4 - EBX */
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.long 0 /* 8 - ECX */
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.long 0 /* 12 - EDX */
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.long 0 /* 16 - ESI */
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.long 0 /* 20 - EDI */
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/* 256 byte buffer, used by int10 */
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.globl asm_realmode_buffer
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asm_realmode_buffer:
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.skip 256
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.code32
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.globl asm_realmode_call
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asm_realmode_call:
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/* save all registers to the stack */
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pusha
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pushf
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movl %esp, __stack
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movl %esp, %ebp
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/*
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* This function is called with regparm=0 and we have to skip the
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* 36 bytes from pushf+pusha. Hence start at 40.
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* Set up our call instruction.
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*/
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movl 40(%ebp), %eax
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mov %ax, __lcall_instr + 1
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andl $0xffff0000, %eax
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shrl $4, %eax
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mov %ax, __lcall_instr + 3
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wbinvd
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setup_registers
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enter_real_mode
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prepare_for_irom
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__lcall_instr = PTR_TO_REAL_MODE(.)
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.byte 0x9a
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.word 0x0000, 0x0000
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enter_protected_mode
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/* restore stack pointer, eflags and register values and exit */
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movl __stack, %esp
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popf
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popa
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ret
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.globl __realmode_interrupt
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__realmode_interrupt:
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/* save all registers to the stack and store the stack pointer */
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pusha
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pushf
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movl %esp, __stack
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movl %esp, %ebp
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/*
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* This function is called with regparm=0 and we have to skip the
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* 36 bytes from pushf+pusha. Hence start at 40.
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* Prepare interrupt calling code.
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*/
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movl 40(%ebp), %eax
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movb %al, __intXX_instr + 1 /* intno */
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setup_registers
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enter_real_mode
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prepare_for_irom
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__intXX_instr = PTR_TO_REAL_MODE(.)
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.byte 0xcd, 0x00 /* This becomes intXX */
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enter_protected_mode
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/* restore stack pointer, eflags and register values and exit */
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movl __stack, %esp
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popf
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popa
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ret
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/*
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* This is the 16-bit interrupt entry point called by the IDT stub code.
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*
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* Before this code code is called, %eax is pushed to the stack, and the
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* interrupt number is loaded into %al. On return this function cleans up
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* for its caller.
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*/
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.code16
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__interrupt_handler_16bit = PTR_TO_REAL_MODE(.)
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push %ds
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push %es
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push %fs
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push %gs
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/* Clear DF to not break ABI assumptions */
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cld
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/*
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* Clean up the interrupt number. We could do this in the stub, but
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* it would cost two more bytes per stub entry.
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*/
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andl $0xff, %eax
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pushl %eax /* ... and make it the first parameter */
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enter_protected_mode
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/* Call the C interrupt handler */
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movl $interrupt_handler, %eax
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call *%eax
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enter_real_mode
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/*
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* Restore all registers, including those manipulated by the C
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* handler
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*/
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popl %eax
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pop %gs
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pop %fs
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pop %es
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pop %ds
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popal
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iret
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.globl asm_realmode_code_size
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asm_realmode_code_size:
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.long . - asm_realmode_code
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