Compile and Use Your Own Glibc

Easily compile and use multiple glibc on a single machine.

Get source and compile

I’ll store my source at ~/src/glibc/

you can download sources of glibc from hit mirror, or tsinghua tuna or official

here take glibc-2.23 as an example, after downloading the source

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
cd ~/src/glibc
mkdir glibc-2.23-{build,out}
cd glibc-2.23-build
# -Wno-error will override -Werror which will make compilation fail on warnings
# -O3, if you specify CFLAGS, you must give it -Ox (glibc cannot be compiled without optimization: https://gnu.org/software/libc/manual/html_mono/libc.html#toc-Installing-the-GNU-C-Library)
# -g will generate embed debug information
../glibc-2.23/configure --prefix=~/src/glibc/glibc-2.23-out CFLAGS="-Wno-error -O3 -g" # this is important
# make # compile with single thread, slow: took me about 14 minutes
make -j`nproc` # faster: took me under 2 minutes
# make -j$((`nproc`+1)) # https://unix.stackexchange.com/questions/208568/how-to-determine-the-maximum-number-to-pass-to-make-j-option
make install # install to what you have configured in the `--prefix` (so mine will be installed to ~/src/glibc/glibc-2.23-out)

use mgcc to compile programs

mgcc

mgcc is just a shell wrapper that wraps the gcc command, you can compile programs same way as you would in gcc.
you can also specify --glibc_install with the installation path of some version of glibc to switch between different glibc’s: mgcc --glibc_install ~/src/glibc/glibc-2.32-out -g -o main main.c

You can find my most up to date mgcc at .dotfiles/bin/mgcc

vim ~/bin/mgcc

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
#!/bin/sh

glibc_install=~/src/glibc/glibc-2.23-out

print_help() {
  echo "$0 [--glibc_install GLIBC_INSTALL_PATH] gcc_args"
}

while [[ $# -ge 1 ]]
do
  key="$1"
  case $key in
    --glibc_install)
      glibc_install="$2"
      shift
      ;;
    -h)
      print_help
      exit 0
      ;;
    *)
      others+=("$1")
      ;;
  esac
  shift
done

gcc \
  -L "${glibc_install}/lib" \
  -I "${glibc_install}/include" \
  -Wl,--rpath="${glibc_install}/lib" \
  -Wl,--dynamic-linker="${glibc_install}/lib/ld-linux-x86-64.so.2" \
  "${others[@]}"

run & debug

vim main.c

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char const *argv[])
{
    void *p1 = malloc(0x70);
    void *p2 = malloc(0x70);
    free(p1);
    free(p2);
    free(p1);
    return 0;
}

you can check if your mgcc works after compile mgcc -g -o main main.c:

1
2
3
4
ldd main
# linux-vdso.so.1 (0x00007ffd36f9a000)
# libc.so.6 => /home/sky/src/glibc/glibc-2.23-out/lib/libc.so.6 (0x00007fac09658000)
# /home/sky/src/glibc/glibc-2.23-out/lib/ld-linux-x86-64.so.2 => /usr/lib64/ld-linux-x86-64.so.2 (0x00007fac0981b000)

tell gdb where to look for source code: dir ~/src/glibc/glibc-2.23/malloc

1
2
3
4
gdb main
# ...
pwndbg> dir ~/src/glibc/glibc-2.23/malloc/
# ...

completion

if you are using zsh and oh-my-zsh (you should), you can add a line: compdef mgcc=gcc to your ~/.zshrc file
this will allow mgcc to use gcc’s completion

run others’ program with your libc

CLI

1
2
3
LD_PRELOAD=./libc.so ./program
# or https://pullp.github.io/2020/11/06/11-glibc-basics/#2-2-run-with-specific-glibc
LD_PRELOAD=./libc.so ./ld.so ./program

pwntools

1
2
3
4
5
#coding:utf-8
from pwn import *

io = process("./program", env={"LD_PRELOAD":"./libc.so"})
io = process(["./ld.so", "./program"], env={"LD_PRELOAD":"./libc.so"})