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-rw-r--r--arch/x86/lib/bios_asm.S281
1 files changed, 281 insertions, 0 deletions
diff --git a/arch/x86/lib/bios_asm.S b/arch/x86/lib/bios_asm.S
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+++ b/arch/x86/lib/bios_asm.S
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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
+
+ /* 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