使用 __asm__ 命令后 C 函数不返回

Question

我正在尝试使用指南从头开始构建操作系统，https://github.com/cfenollosa/os-tutorial。 到目前为止，我已经调试了我所做的项目（第 16 章），当我尝试运行它时遇到了一个问题，我发现调用 void port_byte_out(unsigned short port, unsigned char data) 后 ip 没有变回父函数。

• ports.h - 被调用函数的头文件

unsigned char port_byte_in(unsigned short port);
void port_byte_out(unsigned short port, unsigned char data);
unsigned short port_word_in(unsigned short port);
void port_word_out(unsigned short port, unsigned short data);

• ports.c - 被调用函数的代码文件

    unsigned char result;
    __asm__ ( " in %%dx , %%al " : "=a" ( result ) : "d" ( port ));
    return result ;
}

void port_byte_out ( unsigned short port , unsigned char data ) {
    __asm__ ( "out %%al , %%dx " : : "a" ( data ) , "d" ( port ));
}

unsigned short port_word_in ( unsigned short port ) {
    unsigned short result ;
    __asm__ ( " in %%dx , %%ax " : "=a" ( result ) : "d" ( port ));
    return result;
}

void port_word_out ( unsigned short port , unsigned short data ) {
    __asm__ ( " out %%ax , %%dx " : : "a" ( data ) , "d" ( port ));
}

• screen.c: set_cursor_offset(int) - 调用函数的代码

void set_cursor_offset(int offset) {
    offset /= 2;
    port_byte_out(REG_SCREEN_CTRL, 14);
    port_byte_out(REG_SCREEN_DATA, (unsigned char)(offset >> 8));
    port_byte_out(REG_SCREEN_CTRL, 15);
    port_byte_out(REG_SCREEN_DATA, (unsigned char)(offset & 0xff));
}

• makefile - 可能是非常规使用的东西.. 抱歉，我是新手 :)

# $@ = target file
# $< = first dependcy
# $^ = all dependecies

C_SOURCES = $(wildcard kernel/*.c drivers/*.c)
HEADERS = $(wildcard kernel/*.h drivers/*.h)
OBJ = ${C_SOURCES:.c=.o}

CC = /usr/local/cross/bin/i686-elf-gcc
LD = /usr/local/cross/bin/i686-elf-ld
GDB = gdb

CFLAGS = -g

image.bin: boot_sector.bin kernel.bin
    cat $^ > $@

kernel.bin: boot/kernel_entry.o ${OBJ}
    ${LD} -o $@ -Ttext 0x1000 $^ --oformat binary

kernel.elf: boot/kernel_entry.o ${OBJ}
    ${LD} -g -o $@ -Ttext 0x1000 $^

run: image.bin 
    qemu-system-x86_64 -fda $<

debug: image.bin kernel.elf
    qemu-system-x86_64 -s -fda image.bin &
    ${GDB} -ex "target remote localhost:1234" -ex "symbol-file kernel.elf"

%.o: */%.c ${HEADERS}
    ${CC} ${FLAGS} -ffreestanding -c $< -o $@

%.o: %.asm
    nasm $< -f elf -o $@

%.bin: */%.asm
    nasm $< -f bin -o $@

clean:
    rm -rf *.bin *.dis *.o *.elf
    rm kernel/*.bin kernel/*.o boot/*.bin boot/*.o
    rm drivers/*.bin drivers/*.o
    rm image.bin

• 文件树-

.
├── bin
├── boot
│   ├── 32bit-gdt.asm     --> gdt table
│   ├── boot_sector.asm   --> boot sector
│   ├── disk_load.asm     --> read from disk function
│   ├── kernel_entry.asm  --> enter kernel - defines kernel_main
│   ├── print_32pm.asm    --> protected mode print(used before using the kernel functions)
│   ├── print.asm         --> real mode print
│   ├── print_hex.asm     --> real mode print hex nums
│   └── switch_32pm.asm   --> asm for switching to protected mode
├── drivers
│   ├── ports.c           --> talking to ports through the functions here
│   ├── ports.h           --> ports.c header file
│   ├── screen.c          --> screen memory writing, cursor and print functions
│   └── screen.h          --> screen.c header file
├── kernel
│   └── kernel_main.c     --> the kernel main
└── Makefile

4 directories, 14 files

Answer 1

我设法找到了一个解决方案，即使它不遵循传统的编码方式 - 它也有效.. 我只是按原样使用了 asm 函数中的代码 手动内联它们 为什么在我不知道也没有线索之前它不起作用，如果有人有任何可能的想法，我想理解一个合理的解释。 感谢任何试图提供帮助的人！