Estimated build time: 3 minutes Estimated required disk space: 132 MB |
We won't be compiling a new kernel image yet. We'll do that after we have finished the installation of the basic system software in this chapter. But because certain software needs the kernel header files, we're going to unpack the kernel archive now and set it up so that we can compile the packages that need the kernel.
The kernel configuration file is created by running the following command:
make mrproper && yes "" | make config && make dep && mkdir $LFS/usr/include/asm && cp include/asm/* $LFS/usr/include/asm && cp -R include/linux $LFS/usr/include |
make mrproper: This will ensure that the kernel tree is absolutely clean. We do this because the kernel team recommend that this is done prior to each kernel compilation, and that we shouldn't rely on the source tree being automatically clean after untarring.
yes "" | make config: This runs make config and answers with the default answer to every question the config script asks the user (it does this by simply doing the equivalent of hitting the Enter key, thus accepting the default Y and N answers to the questions). We're not configuring the real kernel here, we just need to have some sort of configure file created so that we can run make dep next that will create a few header files in include/linux, like version.h, among others, that we will need to compile Glibc and other packages later in chroot.
make dep: make dep checks dependencies and sets up the dependencies file. We don't really care about the dependency checks, but what we do care about is that make dep creates those aforementioned files in include/linux we will be needing later on.
mkdir $LFS/usr/include/asm and cp include/asm/* $LFS/usr/include/asm: This copies the platform-specific assembler kernel header files to $LFS/usr/include/asm.
cp -R include/linux $LFS/usr/include: This command copies the cross-platform kernel header files to $LFS/usr/include.
In the past, it was common practice for people to symlink the /usr/include/linux and asm directories to /usr/src/linux/include/linux and asm respectively. This is a bad idea as this extract from a post by Linus Torvalds to the Linux Kernel Mailing List points out:
I would suggest that people who compile new kernels should: - not have a single symbolic link in sight (except the one that the kernel build itself sets up, namely the "linux/include/asm" symlink that is only used for the internal kernel compile itself) And yes, this is what I do. My /usr/src/linux still has the old 2.2.13 header files, even though I haven't run a 2.2.13 kernel in a _loong_ time. But those headers were what glibc was compiled against, so those headers are what matches the library object files. And this is actually what has been the suggested environment for at least the last five years. I don't know why the symlink business keeps on living on, like a bad zombie. Pretty much every distribution still has that broken symlink, and people still remember that the linux sources should go into "/usr/src/linux" even though that hasn't been true in a _loong_ time. |
The relevant part here is where he states that the headers should be the ones which glibc was compiled against. These are the headers which should remain accessible and so by copying them, we ensure that we follow these guidelines. Also note that as long as you don't have those symlinks, it is perfectly fine to have the kernel sources in /usr/src/linux.
the linux kernel and the linux kernel headers
The Linux kernel is at the core of every Linux system. It's what makes Linux tick. When a computer is turned on and boots a Linux system, the very first piece of Linux software that gets loaded is the kernel. The kernel initializes the system's hardware components such as serial ports, parallel ports, sound cards, network cards, IDE controllers, SCSI controllers and a lot more. In a nutshell the kernel makes the hardware available so that the software can run.
These are the files we copy to /usr/include/{linux,asm} in chapter 5. They should match those which glibc was compiled against and so should not be replaced when upgrading the kernel. They are essential for compiling many programs.
Linux-2.4.8 needs the following to be installed:
bash: sh
binutils: ar, as, ld, nm, objcopy
fileutils: chown, cp, ln, mkdir, mv, rm
findutils: find, xargs
gcc: gcc
grep: grep
make: make
mawk: awk
modutils: depmod, genksyms
net-tools: hostname
sed: sed
sh-utils: basename, date, expr, pwd, uname, whoami, yes
textutils: cat, md5sum, sort, tail, touch, tr