gcc - 我的内核原型(prototype)存在问题(x86_64)

Question

我在学习汇编的同时尝试了解内核的工作原理，并且在学习如何成功创建可启动的 x86_64 内核的过程中，我遇到了一个问题:
我尝试使用 0xB8000 中的 VGA 缓冲区成功输出一些带有“main.c”(下面的所有文件)中函数的文本，就像我对 32 位版本内核所做的那样原型(prototype)，但不同的是启动文件不同。
这里的问题是，当我对 32 位版本使用完全相同的函数时，它成功打印到屏幕上，但是当使用新文件达到长模式时(multiboot.S 和 >start.S)这不会发生，在 qemu 中测试时屏幕只是变黑，几秒钟后它崩溃并显示错误消息:

warning: TCG doesn't support requested feature: CPUID.01H:ECX.vmx [bit 5]
qemu-system-x86_64: Trying to execute code outside RAM or ROM at 0x00000000000a0000

为什么会发生这种情况？ VGA 缓冲区不在 0xB8000 中，*.S 文件有问题吗？预先感谢!
我将在此处粘贴内核文件:
内核由 4 个文件组成:“main.c”、“start.S”、“multiboot.S”和链接描述文件“linker.ld”。
这3个文件链接并编译没有任何错误，文件如下:这是main.c(你会看到一个“basiccolors.h”，这个文件只是定义了vga颜色代码)

#include "basiccolors.h"
#include <stddef.h>
#include <stdint.h>

volatile uint16_t* vga_buffer = (uint16_t*)0xB8000; /* memory location of the VGA textmode buffer */
/* Columns and rows of the VGA buffer */
const int VGA_COLS = 80; 
const int VGA_ROWS = 25;

/* We start displaying text in the top-left of the screen (column = 0, row = 0) */
int term_col = 0;
int term_row = 0;
uint8_t term_color = WHITE_TXT; /* This color and others are defined in basiccolors.h */

/* term_init() : This function initiates the terminal by clearing it */
void term_init()
{
    /* Clear the textmode buffer */
    for (int col = 0; col < VGA_COLS; col ++)
    {
        for (int row = 0; row < VGA_ROWS; row ++)
        {
            /* The VGA textmode buffer has size (VGA_COLS * VGA_ROWS) */
            /* Given this, we find an index into the buffer for our character */
            const size_t index = (VGA_COLS * row) + col;
            /* Entries in the VGA buffer take the binary form BBBBFFFFCCCCCCCC, where: */
            /* - B is the background color */
            /* - F is the foreground color */
            /* - C is the ASCII character */
            /*  Now we set the character to blank (a space character)   */          
        vga_buffer[index] = ((uint16_t)term_color << 8) | ' '; 
        }
    }
}

/* term_putc(char c) : This function places a single character onto the  screen */
void term_putc(char c)
{
    /* We don't want to display all characters, for example, the newline ones */
    switch (c)
    {
    case '\n': /* Newline characters should return the column to 0, and increment the row */
        {
            term_col = 0;
            term_row ++;
            break;
        }

    default: /* Normal characters just get displayed and then increment the column */
        {
        /* Like before, calculate the buffer index */           
        const size_t index = (VGA_COLS * term_row) + term_col; 
        vga_buffer[index] = ((uint16_t)term_color << 8) | c;
        term_col ++;
        break;
        }
    }

/* We need to reset the column to 0, and increment the row to get to a new line */
    if (term_col >= VGA_COLS)
    {
        term_col = 0;
        term_row ++;
    }

/* we get past the last row, so we need to reset both column and row to 0 in order to loop back to the top of the screen */
    if (term_row >= VGA_ROWS)
    {
        term_col = 0;
        term_row = 0;
    }
   }

/* term_print : prints an entire string onto the screen, remember to use the "\n" and that short of things */
void term_print(const char* str)
{
    for (size_t i = 0; str[i] != '\0'; i ++) /* Keep placing characters until we hit the null-terminating character ('\0') */
        term_putc(str[i]);
}
/* Main function of the kernel, the one that is called at the end of the loading */
void kmain(void)
{
    /* Now we should initialize the interfaces */
    term_init(); /* VGA basic interface, in "basicoutput.c/h" */
    term_print("CKA Cobalt release                                                      [0-0-1]\n");
};

这是开始。S:

    .extern kmain

    .section .data

    .align 16
gdtr:
gdtr_limit:
    .word (global_descriptor_table_end - global_descriptor_table) - 1
gdtr_pointer:
    .int global_descriptor_table

    .global global_descriptor_table
global_descriptor_table:
null_descriptor:
    .quad 0x0000000000000000
code_descriptor:
    .quad 0x0020980000000000
data_descriptor:
    .quad 0x0000900000000000
global_descriptor_table_end:

    .global null_segment
    .set null_segment, (null_descriptor - global_descriptor_table)
    .global code_segment
    .set code_segment, (code_descriptor - global_descriptor_table)
    .global data_segment
    .set data_segment, (data_descriptor - global_descriptor_table)

multiboot_magic:
    .space 4
multiboot_info:
    .space 4

    .section .bss

    .global kernel_pagetable
    .align 0x1000
kernel_pagetable:
pml4:
    .space 0x1000
pdpt:
    .space 0x1000
pd:
    .space 0x1000
kernel_pagetable_end:

    .global kernel_stack
kernel_stack:
    .space 0x1000
kernel_stack_end:

    .section .text
    .code32

    .global start

start:
    cli

# store multiboot parameters in .data
    mov %eax, multiboot_magic
    mov %ebx, multiboot_info

# zerofill .bss
    cld
    mov $bss, %edi
    mov $bss_end, %ecx
    sub %edi, %ecx
    xor %eax, %eax
    rep stosb

# create pagetable for identity mapping lower 2 megabytes
# make minimal page table entries
    .set pml4_entry, (pdpt + 0x03)
    .set pdpt_entry, (pd + 0x03)
    .set pd_entry, 0b10000011
    movl $pml4_entry, pml4
    movl $pdpt_entry, pdpt
    movl $pd_entry, pd

# setup long mode
# load global descriptor table
    lgdt (gdtr)

# enable Physical Address Extension (PAE)
    mov %cr4, %eax
    bts $5, %eax
    mov %eax, %cr4

# set up page table
    mov $kernel_pagetable, %eax
    mov %eax, %cr3

# set up long mode
    .set EFER_MSR_ADDRESS, 0xC0000080
    mov $EFER_MSR_ADDRESS, %ecx
    rdmsr
    bts $8, %eax
    wrmsr

# enable paging
    mov %cr0, %eax
    bts $31, %eax
    mov %eax, %cr0

# long jump to set code segment
    ljmp $code_segment, $longmode_start

    .code64
longmode_start:
# data segment selector to all data segments
    mov $data_segment, %bx
    mov %bx, %ds
    mov %bx, %es
    mov %bx, %fs
    mov %bx, %gs

# null segment selector to ss
    mov $null_segment, %bx
    mov %bx, %ss

# set up kernel stack
    mov $kernel_stack_end, %rsp
    push $0     # debugger backtrace stops here

# call kmain
    mov multiboot_magic, %edi
    mov multiboot_info, %esi
    call kmain

# hang the computer
    cli
hang:
    hlt
    jmp hang  

这是多重引导。S:

    .set MULTIBOOT_PAGE_ALIGN, 1 << 0
    .set MULTIBOOT_MEM_INFO, 1 << 1
    .set MULTIBOOT_AOUT_KLUDGE, 1 << 16
    .set MULTIBOOT_MAGIC, 0x1BADB002
    .set MULTIBOOT_FLAGS, MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEM_INFO | MULTIBOOT_AOUT_KLUDGE
    .set MULTIBOOT_CHECKSUM, -(MULTIBOOT_MAGIC + MULTIBOOT_FLAGS)

    .section .mboot
    .align 4

    .global multiboot_header

multiboot_header:
    .int MULTIBOOT_MAGIC
    .int MULTIBOOT_FLAGS
    .int MULTIBOOT_CHECKSUM
    .int multiboot_header
    .int text
    .int data_end
    .int kernel_end
    .int start

这是我的 linker.ld:

OUTPUT_FORMAT("elf64-x86-64")
OUTPUT_ARCH(i386:x86-64)
ENTRY(start)

phys = 0x0100000;

SECTIONS
{
    . = phys;
    kernel_start = .;

    .text ALIGN(4096) : AT( ADDR(.text) )
    {
        text = .;
        *(.mboot)  /* Put Multiboot header section in the beginning of .text section */
        *(.text)
        *(.rodata)
        text_end = .;
    }

    .data ALIGN(4096) : AT( ADDR(.data) )
    {
        data = .;
        *(.data)
        data_end = .;
    }

    .bss ALIGN(4096) : AT( ADDR(.bss) )
    {
        bss = .;
        *(.bss)
        bss_end = .;
    }

    kernel_end = .;
}  

所有这些代码都是通过以下命令编译和链接的:
正在编译...

x86_64-elf-gcc -ffreestanding -mcmodel=large -mno-red-zone -mno-mmx -mno-sse -mno-sse2 -c <file> -o <object-file>

和链接:

x86_64-elf-gcc -ffreestanding -T linker.ld multiboot.o start.o main.o -o kernel.bin -nostdlib -lgcc  

此命令是 osdev.com 在教程 http://wiki.osdev.org/Creating_a_64-bit_kernel 中建议的所有内容均使用 x86_64 架构的 gcc 交叉编译器进行编译和链接。

Answer 1

使用 -kernel 参数时，QEMU 不支持 ELF64 可执行文件。您需要使用 multiboot2 兼容加载程序(例如 GRUB2)来启动内核。不幸的是，您还需要将多重引导 header 更改为 multiboot2 compliant 。您可以将 multiboot.S 文件替换为:

.section .mboot
.code32
.align 8

    # constants for multiboot2 header:
    .set MAGIC2,    0xe85250d6
    .set ARCH2,     0                  # i386 protected mode
    .set CHECKSUM2, (-(MAGIC2 + ARCH2 + (mboot2_end - mboot2_start)) & 0xffffffff)

     /* multiboot2 header */
mboot2_start:
    .long MAGIC2
    .long ARCH2
    .long mboot2_end - mboot2_start
    .long CHECKSUM2
    .word  0                           # type
    .word  0                           # flags
    .long  8                           # size
mboot2_end:

您按照之前的方式进行编译。有一个问题 - 为了确保此 header 最终不会被推到文件的前 8kb 之外，您可能需要在链接时指定 4kb 页面:

x86_64-elf-gcc -z max-page-size=0x1000 -ffreestanding -T linker.ld \
    multiboot.o start.o main.o -o kernel.bin -nostdlib -lgcc

添加 -z max-page-size=0x1000 强制最大页面大小为 4kb。