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Tutorial 7: Verifying binary portability with libcheck

<< Back to Tutorial 6: Introducing additional static libraries | Tutorial index

Throughout this tutorial set, we have taught you how to statically link your application to their dependencies. However it is easy to make a mistake and accidentally dynamically link to a dependency. Holy Build Box provides a tool -- libcheck -- which helps you with checking whether your binary is linked to any non-essential libraries.

Using libcheck

The libcheck command can be found inside the Holy Build Box environment. Its usage format is:

libcheck <FILES>

For example, let's compile the hello world from tutorial 1, while dynamically linking it to zlib:

docker run -t -i --rm \
  -v `pwd`:/io \
  phusion/holy-build-box-64:latest \
  /hbb_exe/activate-exec \
  gcc /io/hello.c -o /io/hello /usr/lib64/libz.so.1

Notice that we don't use activation command /hbb_exe/activate-exec.

Use ldd to verify that it is indeed dynamically linked to zlib:

$ ldd hello
    linux-vdso.so.1 =>  (0x00007ffe28054000)
    libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f216b1ff000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f216ae3a000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f216b418000)

If you invoke libcheck, it should complain about this fact:

$ docker run -t -i --rm \
  -v `pwd`:/io \
  phusion/holy-build-box-64:latest \
  /hbb_exe/activate-exec \
  libcheck /io/hello
...
/io/hello is linked to non-system libraries: ['/lib64/libz.so.1']

Adding libcheck to your compilation script

We recommend calling libcheck from your compilation script, so that you are warned about potential issues. For example, here is how the Nginx compilation script would look like:

#!/bin/bash
set -e

# Activate Holy Build Box environment.
source /hbb_exe_gc_hardened/activate

set -x

# Install static PCRE
tar xzf /io/pcre-8.37.tar.gz
cd pcre-8.37
env CFLAGS="$STATICLIB_CFLAGS" CXXFLAGS="$STATICLIB_CXXFLAGS" \
  ./configure --prefix=/hbb_exe_gc_hardened --disable-shared --enable-static
make
make install
cd ..

# Extract and enter source
tar xzf /io/nginx-1.8.0.tar.gz
cd nginx-1.8.0

# Compile
sed -i 's|-lssl -lcrypto|-lssl -lcrypto -lz -ldl|' auto/lib/openssl/conf
./configure --with-http_ssl_module --with-ld-opt="$LDFLAGS"
make
make install

# Verify result
hardening-check -b /usr/local/nginx/sbin/nginx
libcheck /usr/local/nginx/sbin/nginx

# Copy result to host
cp /usr/local/nginx/sbin/nginx /io/

Conclusion

Congratulations, you have reached the end of the tutorials! You may now be interested in reading the guides and the caveats.

Happy building.