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. It 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-0.9.20 directory. There run the following command:

make menuconfig

Next set the following configuration options in the menu:

• Target architecture features and options: set target CPU to 486 and leave the rest at the defaults. Do not forget to set the correct kernel source. Fill in $(MYBOOT)/linux-2.4.21. MYBOOT must be in normal (round) parentheses.
• General Library settings: disable support for global constructors and destructors and profiling, leave the rest at the defaults.
• Networking support: enable RPC support, it's useful for NFS mounts.
• Library installation options. This it the trickiest part.
  • Set shared Library Loader path (first item) to /lib. This is the libraries will be loaded on the target diskette, so any prefix must be left out.
  • Set uClibc environment directory (second item) to
    $(MYBOOT)/uclibc-dev. This is where all files will end up that are needed by the C compiler when compiling and linking programs with uClibc.

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=$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.