The following applies to the original version of LFS from which this book is based. LFS-Multilib only targets the x86_64 CPU architecture. LFS-Multilib must be built using an x86_64 Linux distribution running at least Linux kernel version 3.4.0, with support for 32-bit and x32 ABI executables enabled.
The primary target architectures of LFS are the AMD/Intel x86 (32-bit) and x86_64 (64-bit) CPUs. On the other hand, the instructions in this book are also known to work, with some modifications, with the Power PC and ARM CPUs. To build a system that utilizes one of these CPUs, the main prerequisite, in addition to those on the next few pages, is an existing Linux system such as an earlier LFS installation, Ubuntu, Red Hat/Fedora, SuSE, or other distribution that targets the architecture that you have. Also note that a 32-bit distribution can be installed and used as a host system on a 64-bit AMD/Intel computer.
Some other facts about 64-bit systems need to be added here. When compared to a 32-bit system, the sizes of executable programs are slightly larger and the execution speeds are only slightly faster. For example, in a test build of LFS-6.5 on a Core2Duo CPU based system, the following statistics were measured:
Architecture Build Time Build Size
32-bit 198.5 minutes 648 MB
64-bit 190.6 minutes 709 MB
As you can see, the 64-bit build is only 4% faster and is 9% larger than the 32-bit build. The gain from going to a 64-bit system is relatively minimal. Of course, if you have more than 4GB of RAM or want to manipulate data that exceeds 4GB, the advantages of a 64-bit system are substantial.
The default 64-bit build that results from LFS is considered a "pure" 64-bit system. That is, it supports 64-bit executables only. Building a "multi-lib" system requires compiling many applications twice, once for a 32-bit system and once for a 64-bit system. This is not directly supported in LFS because it would interfere with the educational objective of providing the instructions needed for a straightforward base Linux system. You can refer to the Cross Linux From Scratch project for this advanced topic.
This LFS-Multilib fork is a modification of the LFS build instructions to build a "multi-lib" system, using 32-bit, 64-bit, and x32 ABI libraries, while still creating a fully LFS/BLFS compatibible system.
There is one last comment about 64-bit systems. There are some older packages that cannot currently be built in a "pure" 64-bit system or require specialized build instructions. Generally, these packages have some embedded 32-bit specific assembly language instructions that fail when building on a 64-bit system. This includes some Xorg drivers for some legacy video cards at http://xorg.freedesktop.org/releases/individual/driver/. Many of these problems can be worked around, but may require some specialized procedures or patches.