那些 libc 們

一些 libc 實作

  • BSD libc, implementations distributed under BSD operating systems.
  • GNU C Library (glibc), used in Linux, GNU Hurd and GNU/kFreeBSD.
  • Microsoft C Run-time Library, part of Microsoft Visual C++
  • dietlibc, an alternative small implementation of the C standard library (MMU-less)
  • μClibc, a C standard library for embedded μClinux systems (MMU-less)
  • Newlib, a C standard library for embedded systems (MMU-less)
  • klibc, primarily for booting Linux systems.
  • musl, another lightweight C standard library implementation for Linux systems
  • Bionic, originally developed by Google for the Android embedded system operating system, derived from BSD libc.

musl

musl 的目標就要寫出乾淨、有效率、符合標準的 libc 實作， 對於 static linking 也比較有效率， 目前有部份 Linux distrubutions 把 musl 當作預設的 libc (而不是 glibc)， 例如 OpenWRT、Alpine Linux、Void (Linux) 等等。

在 ArchLinux 上可以直接用 pacman 安裝， 或是從 AUR 抓下來自己 build

$ sudo pacman -S musl
$ cat /usr/bin/musl-gcc
#!/bin/sh
exec "${REALGCC:-gcc}" "$@" -specs "/usr/lib/musl/lib/musl-gcc.specs"
$ musl-gcc -static hello.c -o hello; strip hello; ls -l hello

Static Linked Binary’s Size Comparision

C Code :

#include <stdio.h>

int main () {
    printf("Hello World!\n");
}

Result :

# glibc

$ gcc -static hello.c -o hello; strip hello; ls -l hello
-rwxr-xr-x 1 dv users 738808 Jul 22 19:29 hello
$ clang -static hello.c -o hello ; strip hello ; ls -l hello
-rwxr-xr-x 1 dv users 734776 Jul 22 19:32 hello

# BSD libc

$ gcc -static hello.c -o hello; strip hello; ls -l hello
-rwxrwxr-x  1 wdv4758h  wheel  427408 Jul 22 19:31 hello*
$ clang -static hello.c -o hello ; strip hello ; ls -l hello
-rwxrwxr-x  1 wdv4758h  wheel  427264 Jul 22 19:31 hello*

# musl

$ musl-gcc -static hello.c -o hello; strip hello; ls -l hello
-rwxr-xr-x 1 dv dv 5376 Jul 22 22:05 hello
$ musl-clang -static hello.c -o hello; strip hello; ls -l hello
-rwxr-xr-x 1 dv dv 14632 Jul 22 22:06 hello