c - 编译器在函数名称前加下划线的原因是什么？

Question

当我看到 C 应用程序的汇编代码时，像这样:

emacs hello.c
clang -S -O hello.c -o hello.s
cat hello.s

函数名称以下划线为前缀(例如 callq _printf)。为什么这样做，有什么好处？

---

例子:

你好.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int main() {
  char *myString = malloc(strlen("Hello, World!") + 1);
  memcpy(myString, "Hello, World!", strlen("Hello, World!") + 1);
  printf("%s", myString);
  return 0;
}

你好.s

_main:                       ; Here
Leh_func_begin0:
    pushq   %rbp
Ltmp0:
    movq    %rsp, %rbp
Ltmp1:
    movl    $14, %edi
    callq   _malloc          ; Here
    movabsq $6278066737626506568, %rcx
    movq    %rcx, (%rax)
    movw    $33, 12(%rax)
    movl    $1684828783, 8(%rax)
    leaq    L_.str1(%rip), %rdi
    movq    %rax, %rsi
    xorb    %al, %al
    callq   _printf          ; Here
    xorl    %eax, %eax
    popq    %rbp
    ret
Leh_func_end0:

Answer 1

来自 Linkers and Loaders :

At the time that UNIX was rewritten in C in about 1974, its authors already had extensive assember language libraries, and it was easier to mangle the names of new C and C-compatible code than to go back and fix all the existing code. Now, 20 years later, the assembler code has all been rewritten five times, and UNIX C compilers, particularly ones that create COFF and ELF object files, no longer prepend the underscore.

在 C 编译的汇编结果中添加下划线只是作为变通方法出现的名称修改约定。它一直存在(据我所知)没有特别的原因，现在已经进入 Clang。

在汇编之外，C 标准库通常具有带有下划线前缀的实现定义的函数，以向偶然发现它们的普通程序员传达神奇的概念，不要碰这个。 p>