Building uClibc

The trickiest part to get right is probably the C library, especially because we want to use shared libraries. The space savings are tremendous and once this is done right, you can fit many more utilities on a diskette. The directory where the shared libraries exist on the target system (where they will be used) is different from the directory where they exist on the host system. Without special tricks, the binaries that are compiled with uClibc won't run on the host system.

First create the following subdirectories under the myboot directory.

• uclibc-dev is the directory that contains everything you need to compile programs with uClibc. Int contains the include files for the uClibc library and special versions of gcc and similar programs. In fact it is a kind of cross-compiler, albeit for the same processor architecture.
• rootfs is the directory where everything goes that will be on your bootable diskette.

Next cd into the myboot/uClibc directory. There run the following command:

ln -s extra/Configs/Config.i386 Config

Next edit the Config file as follows:

• Your native compiler will probably compile for a 386. If not, you can edit the line with CROSS=
• Change the line with KERNEL_SOURCE to

   
    KERNEL_SOURCE=/home/lennartb/myboot/linux
  

  It is important that this directory matches the kernel that will eventually be used on the boot diskette.
• Check the configuration options. They look reasonable at the moment, except that you have to set LFS = true. Even though large file system support seems unnecessary on old 386 machines with hard disks well under 2GB, some programs will complain if it is not there.
• Below the BIG FAT WARNING: change the line to

    SHARED_LIB_LOADER_PATH=/lib
  

• Change the line with DEVEL_PREFIX to

     DEVEL_PREFIX=/home/lennartb/myboot/uclibc-dev
  

Run the following commands to make and install the library. Note that we do not install the library as root as we do not install it in a system-wide directory.

make
make install
make PREFIX=/home/lennartb/myboot/rootfs install_target

The first command compiles the libraries, the second command installs the development code into the uclibc-dev directory and the last command installs the shared libraries into the rootfs directory. These will end up on the root file system of the bootable diskette.

Compiling with uClibc can be as simple as putting the uclibc-dev directory first in your path and just running make. Note that you cannot run the programs you have just made on the host system.