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