/* SPDX-License-Identifier: GPL-2.0-only */
/* ----------------------------------------------------------------------- *
 *
 *   Copyright (C) 1991, 1992 Linus Torvalds
 *   Copyright 2007 rPath, Inc. - All Rights Reserved
 *
 * ----------------------------------------------------------------------- */

/*
 * The actual transition into protected mode
 */

#include <asm/boot.h>
#include <asm/processor-flags.h>
#include <asm/segment.h>
#include <linux/linkage.h>

        .text
        .code16

/*
 * void protected_mode_jump(u32 entrypoint, u32 bootparams);
 */
SYM_FUNC_START_NOALIGN(protected_mode_jump)
        movl    %edx, %esi              # Pointer to boot_params table

        xorl    %ebx, %ebx
        movw    %cs, %bx
        shll    $4, %ebx
        addl    %ebx, 2f
        jmp     1f                      # Short jump to serialize on 386/486
1:

        movw    $__BOOT_DS, %cx
        movw    $__BOOT_TSS, %di

        movl    %cr0, %edx
        orb     $X86_CR0_PE, %dl        # Protected mode
        movl    %edx, %cr0

        # Transition to 32-bit mode
        .byte   0x66, 0xea              # ljmpl opcode
2:      .long   .Lin_pm32               # offset
        .word   __BOOT_CS               # segment
SYM_FUNC_END(protected_mode_jump)

        .code32
        .section ".text32","ax"
SYM_FUNC_START_LOCAL_NOALIGN(.Lin_pm32)
        # Set up data segments for flat 32-bit mode
        movl    %ecx, %ds
        movl    %ecx, %es
        movl    %ecx, %fs
        movl    %ecx, %gs
        movl    %ecx, %ss
        # The 32-bit code sets up its own stack, but this way we do have
        # a valid stack if some debugging hack wants to use it.
        addl    %ebx, %esp

        # Set up TR to make Intel VT happy
        ltr     %di

        # Clear registers to allow for future extensions to the
        # 32-bit boot protocol
        xorl    %ecx, %ecx
        xorl    %edx, %edx
        xorl    %ebx, %ebx
        xorl    %ebp, %ebp
        xorl    %edi, %edi

        # Set up LDTR to make Intel VT happy
        lldt    %cx

        jmpl    *%eax                   # Jump to the 32-bit entrypoint
SYM_FUNC_END(.Lin_pm32)