diff options
Diffstat (limited to 'arch/x86/lib/bios_asm.S')
| -rw-r--r-- | arch/x86/lib/bios_asm.S | 281 |
1 files changed, 281 insertions, 0 deletions
diff --git a/arch/x86/lib/bios_asm.S b/arch/x86/lib/bios_asm.S new file mode 100644 index 0000000..4faa70e --- /dev/null +++ b/arch/x86/lib/bios_asm.S @@ -0,0 +1,281 @@ +/* + * 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 + + /* 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 + + /* Call the C interrupt handler */ + movl $interrupt_handler, %eax + call *%eax + + enter_real_mode + + /* + * Restore all registers, including those manipulated by the C + * handler + */ + popl %eax + pop %gs + pop %fs + pop %es + pop %ds + popal + iret + + .globl asm_realmode_code_size +asm_realmode_code_size: + .long . - asm_realmode_code |