rt-thread-official/libcpu/ia32/start_gcc.S

/*
 * Copyright (c) 2006-2022, RT-Thread Development Team
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Change Logs:
 * Date           Author       Notes
 * 2006-09-15     QiuYi        The first version.
 * 2012-02-15     aozima       update.
 */

/* the magic number for the multiboot header.  */
#define MULTIBOOT_HEADER_MAGIC      0x1BADB002

/* the flags for the multiboot header.  */
#define MULTIBOOT_HEADER_FLAGS      0x00000003

#define CONFIG_STACKSIZE            8192

/**
 * @addtogroup I386
 */
/*@{*/

.section .init, "ax"

/* the system entry */
.globl _start
_start:
    jmp multiboot_entry

    /* Align 32 bits boundary.  */
    .align  4

    /* multiboot header.  */
multiboot_header:
    /* magic */
    .long   MULTIBOOT_HEADER_MAGIC
    /* flags */
    .long   MULTIBOOT_HEADER_FLAGS
    /* checksum */
    .long   -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)

multiboot_entry:
    movl    $(_end + 0x1000),%esp

    /* reset eflags.  */
    pushl   $0
    popf

    /* rebuild globe describe table */
    lgdt    __gdtdesc

    movl    $0x10,%eax
    movw    %ax,%ds
    movw    %ax,%es
    movw    %ax,%ss
    ljmp    $0x08, $relocated

relocated:
    /* push the pointer to the multiboot information structure.  */
    pushl   %ebx

    /* push the magic value.  */
    pushl   %eax

    call    rtthread_startup

    /* never get here */
spin:
    hlt
    jmp spin

.data
.p2align    2
__gdt:
    .word   0,0,0,0

    .word   0x07FF      /* 8Mb - limit=2047 */
    .word   0x0000
    .word   0x9A00      /* code read/exec */
    .word   0x00C0

    .word   0x07FF      /* 8Mb - limit=2047 */
    .word   0x0000
    .word   0x9200      /* data read/write */
    .word   0x00C0

__gdtdesc:
    .word   0x17
    .long   __gdt

/*@}*/