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|
/* SPDX-License-Identifier: GPL-2.0-only */
#define REALMODE_BASE 0x600
#define RELOCATED(x) (x - __realmode_code + REALMODE_BASE)
#include <arch/ram_segs.h>
/* CR0 bits */
#define PE (1 << 0)
/* This is the intXX 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 int#.
*/
.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
/* In order to be independent of coreboot's position in RAM
* we relocate a part of the code to the low megabyte, so the
* CPU can use it in real-mode. This code lives at __realmode_code.
*/
.globl __realmode_code
__realmode_code:
/* Realmode function return. */
__realmode_ret = RELOCATED(.)
.long 0
/* Realmode IDT pointer structure. */
__realmode_idt = RELOCATED(.)
.word 1023 /* 16 bit limit */
.long 0 /* 24 bit base */
.word 0
/* Preserve old stack */
__stack = RELOCATED(.)
.long 0
/* Register store for realmode_call and realmode_interrupt */
__registers = RELOCATED(.)
.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 __realmode_buffer
__realmode_buffer:
.skip 256
.code32
.globl __realmode_call
__realmode_call:
/* save all registers to the stack */
pusha
pushf
/* Move the protected mode stack pointer to a safe place */
movl %esp, __stack
movl %esp, %ebp
/* This function is called with regparm=0 and we have to
* skip the 36 byte from pushf+pusha. Hence start at 40.
*/
/* entry point */
movl 40(%ebp), %eax
mov %ax, __lcall_instr + 1
andl $0xffff0000, %eax
shrl $4, %eax
mov %ax, __lcall_instr + 3
/* 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 */
/* Activate the right segment descriptor real mode. */
ljmp $RAM_CODE16_SEG, $RELOCATED(1f)
1:
.code16
/* 16 bit code from here on... */
/* Load the segment registers w/ properly configured
* segment descriptors. They will retain these
* configurations (limits, writability, etc.) once
* protected mode is turned off.
*/
mov $RAM_DATA16_SEG, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
/* Turn off protection */
movl %cr0, %eax
andl $~PE, %eax
movl %eax, %cr0
/* Now really going into real mode */
ljmp $0, $RELOCATED(1f)
1:
/* Setup 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
movl $0x1000, %eax
movl %eax, %esp
/* Load 16 bit IDT */
xor %ax, %ax
mov %ax, %ds
lidt __realmode_idt
/* initialize 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 $0x40, %ax
mov %ax, %ds
pop %ax
/* ************************************ */
__lcall_instr = RELOCATED(.)
.byte 0x9a
.word 0x0000, 0x0000
/* ************************************ */
/*
* Here is end of real mode call and time to go back to protected mode.
* Before that its better to store current eax into some memory address
* so that context persist in protected mode too.
*/
mov %eax, __realmode_ret
/* If we got here, we are just about done.
* Need to get back to protected mode.
*/
movl %cr0, %eax
orl $PE, %eax
movl %eax, %cr0
/* Now that we are in protected mode
* jump to a 32 bit code segment.
*/
ljmpl $RAM_CODE_SEG, $RELOCATED(1f)
1:
.code32
mov $RAM_DATA_SEG, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
/* restore proper idt */
lidt idtarg
/* restore stack pointer, eflags and register values */
movl __stack, %esp
popf
popa
/* and exit */
/* return AX from OPROM call */
mov __realmode_ret, %eax
ret
.globl __realmode_interrupt
__realmode_interrupt:
/* save all registers to the stack */
pusha
pushf
/* save the stack pointer */
movl %esp, __stack
movl %esp, %ebp
/* This function is called with regparm=0 and we have to
* skip the 36 byte from pushf+pusha. Hence start at 40.
*/
/* prepare interrupt calling code */
movl 40(%ebp), %eax
movb %al, __intXX_instr + 1 /* intno */
/* 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 */
/* This configures CS properly for real mode. */
ljmp $RAM_CODE16_SEG, $RELOCATED(1f)
1:
.code16 /* 16 bit code from here on... */
/* Load the segment registers w/ properly configured segment
* descriptors. They will retain these configurations (limits,
* writability, etc.) once protected mode is turned off.
*/
mov $RAM_DATA16_SEG, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
/* Turn off protected mode */
movl %cr0, %eax
andl $~PE, %eax
movl %eax, %cr0
/* Now really going into real mode */
ljmpl $0, $RELOCATED(1f)
1:
/* put the stack at the end of page zero. That way we can easily
* share it between real mode and protected mode, because %esp and
* %ss:%sp point to the same memory.
*/
/* setup a stack */
mov $0x0, %ax
mov %ax, %ss
movl $0x1000, %eax
movl %eax, %esp
/* Load 16-bit intXX IDT */
xor %ax, %ax
mov %ax, %ds
lidt __realmode_idt
/* initialize registers for intXX call */
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 */
push %ax
xor %ax, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
pop %ax
__intXX_instr = RELOCATED(.)
.byte 0xcd, 0x00 /* This becomes intXX */
/*
* Here is end of real mode call and time to go back to protected mode.
* Before that its better to store current eax into some memory address
* so that context persist in protected mode too.
*/
mov %eax, __realmode_ret
/* Ok, the job is done, now go back to protected mode coreboot */
movl %cr0, %eax
orl $PE, %eax
movl %eax, %cr0
/* Now that we are in protected mode jump to a 32-bit code segment. */
ljmpl $RAM_CODE_SEG, $RELOCATED(1f)
1:
.code32
mov $RAM_DATA_SEG, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
/* restore coreboot's 32-bit IDT */
lidt idtarg
/* restore stack pointer, eflags and register values and exit */
movl __stack, %esp
popf
popa
/* return AX from OPROM call */
mov __realmode_ret, %eax
ret
/* This is the 16-bit interrupt entry point called by the IDT stub code.
*
* Before this 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 = RELOCATED(.)
push %ds
push %es
push %fs
push %gs
/* Clear DF to not break ABI assumptions */
cld
/* Clean up the interrupt number. We could have done this in the stub,
* but it would have cost 2 more bytes per stub entry.
*/
andl $0xff, %eax
pushl %eax /* ... and make it the first parameter */
/* Switch to protected mode */
movl %cr0, %eax
orl $PE, %eax
movl %eax, %cr0
/* ... and jump to a 32 bit code segment. */
ljmpl $RAM_CODE_SEG, $RELOCATED(1f)
1:
.code32
mov $RAM_DATA_SEG, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
lidt idtarg
/* Call the C interrupt handler */
movl $interrupt_handler, %eax
call *%eax
/* Now return to real mode ... */
ljmp $RAM_CODE16_SEG, $RELOCATED(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 $RAM_DATA16_SEG, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
/* Disable Protected Mode */
movl %cr0, %eax
andl $~PE, %eax
movl %eax, %cr0
/* Now really going into real mode */
ljmp $0, $RELOCATED(1f)
1:
/* Restore real-mode stack segment */
mov $0x0, %ax
mov %ax, %ss
/* Restore 16 bit IDT */
xor %ax, %ax
mov %ax, %ds
lidt __realmode_idt
/* Restore all registers, including those
* manipulated by the C handler
*/
popl %eax
pop %gs
pop %fs
pop %es
pop %ds
popal
iret
.globl __realmode_code_size
__realmode_code_size:
.long . - __realmode_code
.code32
|
