Linux Kernel Compilation
Compilation In computer programming, the translation of source code into object code by a compiler. Wikipedia

Uname Command

Print system information
Print all information
[email protected]:~$ uname -a
Linux kali 4.12.0-kali2-amd64 #1 SMP Debian 4.12.13-1kali2 (2017-10-03) x86_64 GNU/Linux
Print the Kernel Release
[email protected]:~$ uname -r
4.12.0-kali2-amd64

/boot Directory

This directory contains everything required for the boot process except for configuration files not needed at boot time (the most notable of those being those that belong to the GRUB boot-loader) and the map installer. LDP Linux Filesystem Hierarchy /boot
config-4.12.0-kali1-amd64 initrd.img-4.12.0-kali2-amd64 vmlinuz-4.12.0-kali1-amd64
config-4.12.0-kali2-amd64 initrd.img-4.15.0-kali1-amd64 vmlinuz-4.12.0-kali2-amd64
config-4.15.0-kali1-amd64 System.map-4.12.0-kali1-amd64 vmlinuz-4.15.0-kali1-amd64
grub System.map-4.12.0-kali2-amd64
initrd.img-4.12.0-kali1-amd64 System.map-4.15.0-kali1-amd64

config

Installed kernel configuration
[email protected]:~/boot$ ls /boot/config-$(uname -r)
/boot/config-4.12.0-kali2-amd64
[email protected]:~/boot$ file config-4.12.0-kali2-amd64
config-4.12.0-kali2-amd64: Linux make config build file, ASCII text
[email protected]:~/boot$ ls -alh config-4.12.0-kali2-amd64
-rw-r--r-- 1 root root 190K Oct 3 01:58 config-4.12.0-kali2-amd64
[email protected]:~/boot$ cat config-4.12.0-kali2-amd64 | less
#
# Automatically generated file; DO NOT EDIT.
# Linux/x86 4.12.13 Kernel Configuration
#
CONFIG_64BIT=y
CONFIG_X86_64=y
CONFIG_X86=y
CONFIG_INSTRUCTION_DECODER=y
CONFIG_OUTPUT_FORMAT="elf64-x86-64"
CONFIG_ARCH_DEFCONFIG="arch/x86/configs/x86_64_defconfig"
CONFIG_LOCKDEP_SUPPORT=y
CONFIG_STACKTRACE_SUPPORT=y
CONFIG_MMU=y
CONFIG_ARCH_MMAP_RND_BITS_MIN=28
CONFIG_ARCH_MMAP_RND_BITS_MAX=32
CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN=8
CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX=16
CONFIG_NEED_DMA_MAP_STATE=y
CONFIG_NEED_SG_DMA_LENGTH=y
...

initrd

In computing, initrd (initial ramdisk) is a scheme for loading a temporary root file system into memory, which may be used as part of the Linux startup process. initrd and initramfs refer to two different methods of achieving this. Both are commonly used to make preparations before the real root file system can be mounted. Wikipedia
[email protected]:~/boot$ ls /boot/initrd.img-$(uname -r)
/boot/initrd.img-4.12.0-kali2-amd64
[email protected]:~/boot$ file initrd.img-4.12.0-kali2-amd64
initrd.img-4.12.0-kali2-amd64: ASCII cpio archive (SVR4 with no CRC)
[email protected]:~/boot$ ls -alh initrd.img-4.12.0-kali2-amd64
-rw-r--r-- 1 root root 26M Oct 8 22:54 initrd.img-4.12.0-kali2-amd64
[email protected]:~/boot$ mkdir /tmp/temp
[email protected]:~/boot$ cd /tmp/temp/
[email protected]:/tmp/temp$ cp /boot/initrd.img-4.12.0-kali2-amd64 .
[email protected]:/tmp/temp$ (cpio -id; zcat | cpio -id) < initrd.img-4.12.0-kali2-amd64
36 blocks
148321 blocks
[email protected]:/tmp/temp$ ls
bin conf etc init initrd.img-4.12.0-kali2-amd64 kernel lib lib64 run sbin scripts
[email protected]:/tmp/temp$ find . -type f | wc -l
1117
[email protected]:/tmp/temp$ find lib/modules/4.12.0-kali2-amd64/kernel/ -type f | wc -l
662
[email protected]:/tmp/temp$ cd /boot
[email protected]:~/boot$ rm -rf /tmp/temp/

System

In Linux, the System.map file is a symbol table used by the kernel. A symbol table is a look-up between symbol names and their addresses in memory. A symbol name may be the name of a variable or the name of a function. The System.map is required when the address of a symbol name, or the symbol name of an address, is needed. It is especially useful for debugging kernel panics and kernel oopses. The kernel does the address-to-name translation itself when CONFIG_KALLSYMS is enabled so that tools like ksymoops are not required. Wikipedia
[email protected]:~/boot$ ls /boot/System.map-$(uname -r)
/boot/System.map-4.12.0-kali2-amd64
[email protected]:~/boot$ file System.map-4.12.0-kali2-amd64
System.map-4.12.0-kali2-amd64: ASCII text
[email protected]:~/boot$ ls -alh System.map-4.12.0-kali2-amd64
-rw-r--r-- 1 root root 2.9M Oct 3 01:58 System.map-4.12.0-kali2-amd64
[email protected]:~/boot$ cat System.map-4.12.0-kali2-amd64 | less
0000000000000000 D __per_cpu_start
0000000000000000 D irq_stack_union
0000000000000000 A xen_irq_disable_direct_reloc
0000000000000000 A xen_save_fl_direct_reloc
00000000000001c5 A kexec_control_code_size
0000000000004000 d exception_stacks
0000000000009000 D gdt_page
000000000000a000 D espfix_waddr
000000000000a008 D espfix_stack
000000000000a020 D cpu_llc_id
000000000000a040 D cpu_llc_shared_map
000000000000a080 D cpu_core_map
000000000000a0c0 D cpu_sibling_map
000000000000a100 D cpu_info
000000000000a1e8 D cpu_number
000000000000a1f0 D this_cpu_off
000000000000a1f8 D x86_cpu_to_acpiid
000000000000a1fc D x86_cpu_to_apicid
000000000000a1fe D x86_bios_cpu_apicid
000000000000a200 D sched_core_priority
000000000000a240 d cpu_loops_per_jiffy
000000000000a280 d pmc_prev_left
000000000000a480 D cpu_hw_events
000000000000b740 d bts_ctx
000000000000b800 D pqr_state
000000000000b810 d insn_buffer
...
[email protected]:~/boot$ cat /proc/kallsyms | less
0000000000000000 A irq_stack_union
0000000000000000 A __per_cpu_start
0000000000004000 A exception_stacks
0000000000009000 A gdt_page
000000000000a000 A espfix_waddr
000000000000a008 A espfix_stack
000000000000a020 A cpu_llc_id
000000000000a040 A cpu_llc_shared_map
000000000000a080 A cpu_core_map
000000000000a0c0 A cpu_sibling_map
000000000000a100 A cpu_info
000000000000a1e8 A cpu_number
000000000000a1f0 A this_cpu_off
000000000000a1f8 A x86_cpu_to_acpiid
000000000000a1fc A x86_cpu_to_apicid
000000000000a1fe A x86_bios_cpu_apicid
000000000000a200 A sched_core_priority
000000000000a240 A cpu_loops_per_jiffy
000000000000a280 A pmc_prev_left
000000000000a480 A cpu_hw_events
000000000000b740 A bts_ctx
000000000000b800 A pqr_state
000000000000b810 A insn_buffer
000000000000b820 A pt_ctx
000000000000b900 A xen_vcpu_info
000000000000b940 A xen_vcpu_id
...
[email protected]:~/boot$ cat System.map-4.12.0-kali2-amd64 | grep exception_stacks
0000000000004000 d exception_stacks
[email protected]:~/boot$ cat /proc/kallsyms | grep exception_stacks
0000000000004000 A exception_stacks

Vmlinuz

On Linux systems, vmlinux is a statically linked executable file that contains the Linux kernel in one of the object file formats supported by Linux, which includes ELF, COFF and a.out. The vmlinux file might be required for kernel debugging, symbol table generation or other operations, but must be made bootable before being used as an operating system kernel by adding a multiboot header, bootsector and setup routines. Wikipedia
[email protected]:~/boot$ ls /boot/vmlinuz-$(uname -r)
/boot/vmlinuz-4.12.0-kali2-amd64
[email protected]:~/boot$ file vmlinuz-4.12.0-kali2-amd64
vmlinuz-4.12.0-kali2-amd64: Linux kernel x86 boot executable bzImage, version 4.12.0-kali2-amd64 ([email protected]) #1 SMP Debian 4.12.13-1kali2 (2017-10-03), RO-rootFS, swap_dev 0x4, Normal VGA
[email protected]:~/boot$ ls -alh vmlinuz-4.12.0-kali2-amd64
-rw-r--r-- 1 root root 4.2M Oct 3 01:58 vmlinuz-4.12.0-kali2-amd64
[email protected]:~/boot$ mkdir /tmp/vmlinuz
[email protected]:~/boot$ cd /tmp/vmlinuz/
[email protected]:/tmp/vmlinuz$ cp /boot/vmlinuz-4.12.0-kali2-amd64 .
...

/lib/modules/ Directory

The /lib directory contains kernel modules and those shared library images (the C programming code library) needed to boot the system and run the commands in the root filesystem. LDP Linux Filesystem Hierarchy /lib
[email protected]:~$ ls -al /lib/modules/
total 24K
drwxr-xr-x 7 root root 4.0K Dec 23 09:05 .
drwxr-xr-x 18 root root 4.0K Sep 9 19:05 ..
drwxr-xr-x 3 root root 4.0K Sep 10 09:26 4.12.0-kali1-amd64
drwxr-xr-x 3 root root 4.0K Oct 8 22:54 4.12.0-kali2-amd64
drwxr-xr-x 2 root root 4.0K Oct 8 22:59 4.6.0-kali1-amd64
drwxr-xr-x 2 root root 4.0K Oct 8 22:59 4.9.0-kali2-amd64
[email protected]:~$ ls -al /lib/modules/4.12.0-kali2-amd64/
total 4176
drwxr-xr-x 3 root root 4096 Oct 8 22:54 .
drwxr-xr-x 7 root root 4096 Dec 23 09:05 ..
lrwxrwxrwx 1 root root 41 Oct 3 01:58 build -> /usr/src/linux-headers-4.12.0-kali2-amd64
drwxr-xr-x 12 root root 4096 Sep 26 00:17 kernel
-rw-r--r-- 1 root root 1031395 Oct 8 22:54 modules.alias
-rw-r--r-- 1 root root 988746 Oct 8 22:54 modules.alias.bin
-rw-r--r-- 1 root root 4402 Oct 3 01:58 modules.builtin
-rw-r--r-- 1 root root 5907 Oct 8 22:54 modules.builtin.bin
-rw-r--r-- 1 root root 399937 Oct 8 22:54 modules.dep
-rw-r--r-- 1 root root 551428 Oct 8 22:54 modules.dep.bin
-rw-r--r-- 1 root root 402 Oct 8 22:54 modules.devname
-rw-r--r-- 1 root root 133633 Oct 3 01:58 modules.order
-rw-r--r-- 1 root root 772 Oct 8 22:54 modules.softdep
-rw-r--r-- 1 root root 501957 Oct 8 22:54 modules.symbols
-rw-r--r-- 1 root root 618714 Oct 8 22:54 modules.symbols.bin
lrwxrwxrwx 1 root root 42 Oct 3 01:58 source -> /usr/src/linux-headers-4.12.0-kali2-common
[email protected]:~$ ls /usr/src/linux-headers-4.12.0-kali2-common
arch include Makefile scripts
[email protected]:~$ ls /usr/src/linux-headers-4.12.0-kali2-amd64/
arch include Makefile Module.symvers scripts
[email protected]:~$ find /lib/modules/4.12.0-kali2-amd64/kernel/ -type f | wc -l
3403

/usr/src Directory

[email protected]:~$ ls /usr/src
aufs-4.12+20170904 linux-kbuild-4.12
linux-headers-4.12.0-kali2-amd64 volatility-tools
linux-headers-4.12.0-kali2-common

Mainline

[email protected]:~/linux$ ls
arch CREDITS firmware ipc lib net security virt
block crypto fs Kbuild MAINTAINERS README sound
certs Documentation include Kconfig Makefile samples tools
COPYING drivers init kernel mm scripts usr

Configuration Setup

[email protected]:~/linux$ cp /boot/config-4.12.0-kali2-amd64 .config
[email protected]:~/linux$ make oldconfig
<You will be asked configuration questions not answered, for now hit Enter for all of them>
DesignWare Cores SATA support (SATA_DWC) [N/m/?] (NEW)
...
#
# configuration written to .config
#

Compilation Kernel and Modules

[email protected]:~/linux$ make
[email protected]:~/linux$ ls
arch crypto include kernel modules.builtin scripts virt
block Documentation init lib modules.order security
certs drivers ipc MAINTAINERS net sound
COPYING firmware Kbuild Makefile README tools
CREDITS fs Kconfig mm samples usr

Installation Modules

[email protected]:~/linux# make modules_install

Installation Kernel

[email protected]:~/linux# make install

Uname

Reboot your workstation and confirm the new version has been installed, print the Kernel Release
[email protected]:~$ uname -a
Linux kali config-4.15.0-rc4+ #1 SMP Debian 4.12.13-1kali2 (2017-10-03) x86_64 GNU/Linux