我正在实现我自己的内核,我卡住了。我试图将我的内核加载到高半虚拟地址中。我通过身份映射RAM的低1M
来解决身份地址问题。我创建了一个init
段,它被重新定位到内核的物理地址,以便处理分页初始化。我的内核的虚拟偏移量是0xc0000000
。这是我的链接器脚本:
OUTPUT_FORMAT(elf32-i386)
ENTRY(start)
KERNEL_VIRTUAL_OFFSET = 0xC0000000;
SECTIONS
{
. = 1M;
kernel_start = .;
start_init = .;
.init ALIGN(4K) :
{ *(.multiboot);
*(.init);
*(.tables);
}
end_init = .;
. += KERNEL_VIRTUAL_OFFSET;
kernel_high_half_start = .;
.text ALIGN(4K) : AT(ADDR(.text) - KERNEL_VIRTUAL_OFFSET)
{*(.text) }
.data ALIGN(4K) : AT(ADDR(.data) - KERNEL_VIRTUAL_OFFSET)
{ *(.data) }
.rodata ALIGN(4K) : AT(ADDR(.rodata) - KERNEL_VIRTUAL_OFFSET)
{ *(.rodata) }
.bss ALIGN(4K) : AT(ADDR(.bss) - KERNEL_VIRTUAL_OFFSET)
{ *(.bss) }
kernel_high_half_end = .;
kernel_end = . - KERNEL_VIRTUAL_OFFSET;
}
这是我的切入点。我使用GRUB作为引导加载程序。由于init
部分,它成功启动并跳转到我的入口点:
its 32
section .multiboot
;grub bootloader header
align 4
dd 0x1BADB002 ;magic
dd 0x00 ;flags
dd - (0x1BADB002 + 0x00) ;checksum. m+f+c should be zero
; Declarations
global start
extern kmain
extern paging_init
extern kernel_page_directory
section .init
enable_paging:
mov eax, kernel_page_directory
mov cr3, eax
mov eax, cr0
or eax, 0x80000000
mov cr0, eax ; ***** PAGING ENABLED HERE *****
ret
start:
cli ;block interrupts
mov esp, init_stack
call paging_init
call enable_paging
;mov eax, 0xb8000
;mov byte[eax], 'h'
;mov byte[eax+1], 0x7
; Now high half kernel is mapped to the page directory
mov esp, stack_space ;set stack pointer
push ebx ; grub boot info
call kmain
loop:
hlt ;halt the CPU
jmp loop
resb 4096; 4KB small stack for my init section.
init_stack:
section .bss
resb 8192 ;8KB for stack
stack_space:
这是我的代码填充页表和页目录的内核。如您所见,整个代码被链接到init
节中,以避免重定位问题:
page_table_t kernel_page_directory[PAGE_DIR_SIZE]
__attribute__((aligned(PAGE_SIZE))) __attribute__((section(".tables"))) = {0};
page_pointer_t kernel_page_tables[PAGE_TABLE_SIZE]
__attribute__((aligned(PAGE_SIZE))) __attribute__((section(".tables"))) = {0};
page_pointer_t identity_page_table[PAGE_TABLE_SIZE]
__attribute__((aligned(PAGE_SIZE))) __attribute__((section(".tables"))) = {0};
/* Identity map the low 1M
* In early boot stage.
*/
static void __attribute__((section(".init"))) map_identity()
{
//map bios
unsigned int current_page = 0;
for(int i = 0; i < BIOS_PAGE_TABLE_ENTRIES; i++, current_page += PAGE_SIZE)
{
identity_page_table[i] = (current_page) | 0x3;
}
//map init
current_page = INIT_START;
for(int i = INIT_START >> 12 & 0x3FF;
i < ((INIT_START >> 12 & 0x3FF) + (INIT_SIZE / PAGE_SIZE));
i++, current_page += PAGE_SIZE)
{
identity_page_table[i] = (current_page) | 0x3;
}
kernel_page_directory[0] = ((unsigned long)(identity_page_table)) | 0x3;
}
/* Map the kernel memory to its page directory,
* **in early boot stage.
* We don't need to map the init section, we don't need it anymore.
*/
__attribute__((section(".init"))) static void map_kernel_memory()
{
//Identity map the init section
//Start at 1MB i.e. its page aligned.
unsigned int start_index = 256;
unsigned long current_page = KERNEL_START;
for(int i = start_index;
i < start_index + (KERNEL_SIZE / PAGE_SIZE) + 1;
i++, current_page += PAGE_SIZE)
{
kernel_page_tables[i] = current_page | 0x3;
}
kernel_page_directory[KERNEL_DIRECTORY_ENTRY] = ((unsigned long)kernel_page_tables) | 0x3;
}
__attribute__((section(".init"))) void paging_init()
{
map_identity();
map_kernel_memory();
}
我试图指向确切的汇编指令,但这使我的内核工作不正确,我认为这是因为mov cr0, eax
当我启用分页。CR3
不包含kernel_page_directory
或0x3
的地址。一旦启用分页,QEMU就会停止响应,系统会不断重新启动。屏幕正在刷新,然后重复打印。知道为什么会这样吗?我怎样才能修好它?
您的页面目录地址是否与页面对齐?每个页面(帧)的大小为4 KB。我建议为页面目录创建一个结构体,像这样:
typedef struct page_directory{
page_table_t *tables[1024];
size_t tablesPhysical[1024]; // Physical address of page tables
size_t physicalAddr; // Physical address of `tablesPhysical'
} page_directory_t;
因此,您的目录地址必须是4 KB (0x1000)的倍数。James Molloy的教程可能会对你有所帮助。