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问题描述

溢出,

如何使用内联汇编只有我实现的putchar(炭)程序吗?我想这样做是x86-64的装配。究其原因,我这样做是为了实现自己的标准LIB(或至少它的一部分)。以下是我迄今为止:

how can I implement the putchar(char) procedure using inline assembly only? I would like to do this in x86-64 assembly. The reason for me doing this is to implement my own standard-lib (or at least part of it). Here is what I have so far:

void putchar(char c)
{
    /* your code here: print character c on stdout */
    asm(...);
}

void _start()
{
    /* exit system call */
    asm("mov $1,%rax;"
        "xor %rbx,%rbx;"
        "int  $0x80"
    );
}

我用编译:

gcc -nostdlib -o putchar putchar.c

感谢您帮助我!

推荐答案

下面是在海湾合作委员会的x86-64内联汇编的例子 my_putchar (在Intel语法,转换成AT&安培; T应当是微不足道的)。

Here's an example my_putchar in GCC x86-64 inline assembly (in Intel syntax, converting to AT&T should be trivial).

与编译:


gcc -ggdb -masm=intel -o gcc_asm_putchar gcc_asm_putchar.c

编辑: RDI 从破坏寄丢了。固定的。

rdi was missing from clobbered registers. Fixed.

这里的code:

int main(void)
{
    char my_char;

    for (my_char = 'a'; my_char <= 'z'; my_char++)
            my_putchar(my_char);

    my_char = '\n';
    my_putchar(my_char);
    return 0;
}

void my_putchar(char my_char)
{
    int dword_char;
    dword_char = (int)my_char;
    asm volatile(
                    ".intel_syntax noprefix;"
                    "mov r10,rsp;"   // save rsp.
                    "sub rsp,8;"     // space for buffer, align by 8.
                    "mov [rsp],al;"  // store the character into buffer.
                    "mov edi,1;"     // STDOUT.
                    "mov rsi,rsp;"   // pointer to buffer.
                    "mov edx,1;"     // string length in bytes.
                    "mov eax,1;"     // WRITE.
                    "syscall;"       // clobbers rcx & r11.
                    "mov rsp,r10;"   // restore rsp.
                    ".att_syntax prefix;"
                    /* outputs */
                    :
                    /* inputs: eax */
                    : "a"(dword_char)
                    /* clobbered regs */
                    : "rcx", "rdx", "rsi", "rdi", "r10", "r11"
                );
}

这篇关于GCC:内联汇编的putchar(炭)的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

08-19 15:14