我写了一个简单的内核，试图将两个字符写入帧缓冲区。
如果我在内核中定义一个字符串文字，我在启动时会得到以下输出：
Booting 'os'
kernel /boot/kernel.elf
Error 13: Invalid or unsupported executable format
Press any key to continue...
否则，如果我定义了两个字符，我会得到以下内容（请注意＆＃39; ab＆＃39;在输出的开头）：
abBooting 'os'
kernel /boot/kernel.elf
[Multiboot-elf, <0x100000:0x201:0x0>, <0x101000:0x0:0x1000>, shtab=0x102168,
entry=0x1001f0]
我在汇编中编写了加载程序：
global loader ; the entry symbol for ELF
MAGIC_NUMBER equ 0x1BADB002 ; define the magic number constant
FLAGS equ 0x0 ; multiboot flags
CHECKSUM equ -MAGIC_NUMBER ; calculate the checksum
; (magic number + checksum + flags should equal 0)
KERNEL_STACK_SIZE equ 4096 ; size of stack in bytes
section .text: ; start of the text (code) section
align 4 ; the code must be 4 byte aligned
dd MAGIC_NUMBER ; write the magic number to the machine code,
dd FLAGS ; the flags,
dd CHECKSUM ; and the checksum
loader: ; the loader label (defined as entry point in linker script)
mov eax, 0xCAFEBABE ; place the number 0xCAFEBABE in the register eax
mov esp, kernel_stack + KERNEL_STACK_SIZE ; point esp to the start of the
; stack (end of memory area)
extern run
call run
.loop:
jmp .loop ; loop forever
section .bss
align 4 ; align at 4 bytes
kernel_stack: ; label points to beginning of memory
resb KERNEL_STACK_SIZE ; reserve stack for the kernel
#include "io.h"
#include "fb.h"
void run()
{
// try writing message to port
char* c = (char *) 10000;
c[0] = 'a';
c[1] = 'b';
fb_write(c, 2); // this does not cause the error
// fb_write("ab",2); // this line would cause the error
}
有两个外部标题。一个用于IO端口，一个叫做io.h，一个用于写入帧缓冲区，叫做fb.h
这是io.h和实现io.s
io.h：
#ifndef INCLUDE_IO_H
#define INCLUDE_IO_H
/** outb:
* Sends the given data to the given I/O port. Defined in io.s
*
* @param port The I/O port to send the data to
* @param data The data to send to the I/O port
*/
void outb(unsigned short port, unsigned char data);
#endif /* INCLUDE_IO_H */
io.s：
global outb ; make the label outb visible outside this file
; outb - send a byte to an I/O port
; stack: [esp + 8] the data byte
; [esp + 4] the I/O port
; [esp ] return address
outb:
mov al, [esp + 8]
mov dx, [esp + 4]
out dx, al
ret
fb.h
#include "io.h"
// FRAME BUFFER ================================
// Text colors
#define FB_BLACK 0
#define FB_BLUE 1
#define FB_GREEN 2
#define FB_CYAN 3
#define FB_RED 4
#define FB_MAGENTA 5
#define FB_BROWN 6
#define FB_LT_GREY 7
#define FB_DARK_GREY 8
#define FB_LT_BLUE 9
#define FB_LT_GREEN 10
#define FB_LT_CYAN 11
#define FB_LT_RED 12
#define FB_LT_MAGENTA 13
#define FB_LT_BROWN 14
#define FB_WHITE 15
// IO PORTS
#define FB_COMMAND_PORT 0x3D4
#define FB_DATA_PORT 0x3D5
// IO PORT COMMANDS
#define FB_HIGH_BYTE_COMMAND 14 // move cursor command low
#define FB_LOW_BYTE_COMMAND 15 // move cursor command high
/** fb_write_cell:
* used to write a character to a cell in the framebuffer
*
* param i which cell to write to
* param c the ascii char to write
* param fg foreground color
* param bf background color
*/
void fb_write_cell(unsigned int i, char c, unsigned char fg, unsigned char bg);
/** fb_move_cursor:
* used to move the cursor within the frame buffer
*
* param pos position within frame buffer to move cursor to
*/
void fb_move_cursor(unsigned short pos);
/** fb_write:
* write some text to the cursor
*
* param buf pointer to character string
* param len length of string to write
*/
int fb_write(char *buf, unsigned int len);
fb.c
#include "fb.h"
void fb_write_cell(unsigned int i, char c, unsigned char fg, unsigned char bg)
{
char *fb = (char *) 0x000B8000;
fb[i*2] = c;
fb[i*2 + 1] = ((fg & 0x0F) << 4) | (bg & 0x0F);
}
void fb_move_cursor(unsigned short pos) {
outb(FB_COMMAND_PORT, FB_HIGH_BYTE_COMMAND);
outb(FB_DATA_PORT, ((pos>>8) & 0x00FF));
outb(FB_COMMAND_PORT, FB_LOW_BYTE_COMMAND);
outb(FB_DATA_PORT, pos & 0x00FF);
}
int fb_write(char *buf, unsigned int len) {
unsigned int i = 0;
for(i = 0; i < len; i++) {
fb_write_cell(i, buf[i], FB_BLACK, FB_WHITE);
}
return 0;
}
我有一个名为link.ld的链接描述文件和一个Makefile。我使用gcc交叉编译器为i386-elf我使用本指南编译（http://wiki.osdev.org/GCC_Cross-Compiler）。
ENTRY(loader) /* the name of the entry label */
SECTIONS {
. = 0x00100000; /* the code should be loaded at 1 MB */
.text ALIGN (0x1000) : /* align at 4 KB */
{
*(.text) /* all text sections from all files */
}
.rodata ALIGN (0x1000) : /* align at 4 KB */
{
*(.rodata*) /* all read-only data sections from all files */
}
.data ALIGN (0x1000) : /* align at 4 KB */
{
*(.data) /* all data sections from all files */
}
.bss ALIGN (0x1000) : /* align at 4 KB */
{
sbss = .;
*(COMMON) /* all COMMON sections from all files */
*(.bss) /* all bss sections from all files */
ebss = .;
}
}
这是我的makefile
OBJECTS = io.o fb.o loader.o kmain.o
#CC = gcc
CC = /home/albertlockett/opt/cross/bin/i386-elf-gcc
CFLAGS = -m32 -nostdlib -nostdinc -fno-builtin -fno-stack-protector \
-nostartfiles -nodefaultlibs -Wall -Wextra -Werror -c
LDFLAGS = -T link.ld -melf_i386
AS = nasm
ASFLAGS = -f elf
all: kernel.elf
kernel.elf: $(OBJECTS)
ld $(LDFLAGS) $(OBJECTS) -o kernel.elf
os.iso: kernel.elf
cp kernel.elf iso/boot/kernel.elf
genisoimage -R \
-b boot/grub/stage2_eltorito \
-no-emul-boot \
-boot-load-size 4 \
-A os \
-input-charset utf8 \
-quiet \
-boot-info-table \
-o os.iso \
iso
run: os.iso
bochs -f bochsrc.txt -q
%.o: %.c
$(CC) $(CFLAGS) $< -o $@
%.o: %.s
$(AS) $(ASFLAGS) $< -o $@
clean:
rm -rf *.o kernel.elf os.iso
makefile从名为iso的目录的内容构建一个iso。该文件夹包含我在这里获得的预配置grub版本（https://github.com/littleosbook/littleosbook/blob/master/files/stage2_eltorito）和grub的menu.lst文件
的menu.lst：
default=0
timeout=0
title os
kernel /boot/kernel.elf
iso目录的内容：
iso
`-- boot
|-- grub
| |-- menu.lst
| `-- stage2_eltorito
`-- kernel.elf
iso图像在bochs中启动。这是我的bochsrc.txt文件
megs: 32
display_library: term
romimage: file=/usr/share/bochs/BIOS-bochs-latest
vgaromimage: file=/usr/share/bochs/VGABIOS-lgpl-latest
ata0-master: type=cdrom, path=os.iso, status=inserted
boot: cdrom
log: bochslog.txt
clock: sync=realtime, time0=local
cpu: count=1, ips=1000000
com1: enabled=1, mode=file, dev=com1.out
当我尝试启动iso时，是否有人知道为什么内核文件中的字符串文字会产生错误？
答案 0 :(得分：6)
section .text:末尾有一个额外的冒号，因此会创建一个名为.text:的新部分。由于一些模糊的原因，我无法从快速浏览文档中发现，即使未在链接描述文件中列出，也会将此部分发送到输出。如果C代码中没有文字数据，那么幸运的是它仍然属于图像的前8kiB，因此多引导头位于所需部分。如果你有一个字符串文字，你会得到一个新的.rodata部分，而且由于另一个不明原因，它会在.text:之前但在标准.text之后排序。例如：
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000001 00100000 00100000 00001000 2**4
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .rodata 00000005 00101000 00101000 00002000 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
2 .text: 00000018 00101008 00101008 00002008 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
3 .bss 0000100a 00102000 00102000 00003000 2**2
ALLOC
正如你所看到的那样，它不再位于图像的第一个8kiB内，所以grub会非常难过。
TL; DR：在section .text:之后删除多余的冒号。