C function 使用 __asm__ 命令后不返回

Question

我正在嘗試使用指南https://github.com/cfenollosa/os-tutorial從頭開始構建操作系統。 我已經調試了到目前為止所做的項目（第 16 章），當我嘗試運行它時遇到一個問題，我發現 ip 在調用void port_byte_out(unsigned short port, unsigned char data) 。

• ports.h - 調用 function 的 header 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 - 被調用 function 的代碼文件

    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) - 調用者代碼 function

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 - 可能是非常規使用的東西..對不起，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

• 文件樹 -

.
├── 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

我設法找到了一個解決方案，即使不遵循傳統的編碼方式 - 它也有效.. 我只是使用asm函數中的代碼，因為它們手動內聯，為什么它在我不知道並且沒有任何線索之前不起作用如果有人有任何可能的想法，我想理解一個合理的解釋。 感謝任何試圖提供幫助的人！