Linux Kernel boot sequence

http://elmurod.net/en/index.php/archives/625

Execution in Assembly

Entry point for Kernel uncompressed – arch/arm/kernel/head.S
Read processor ID in coprocessor and obtain proc_info_list pointer
Lookup machine type based on mach-id passed by bootloader (R1), get the mach_desc pointer and save mach-id
Determine vailidity of ATAGS pointer (R2) and save
Setup minimal pagetable to get Kernel running on virtual address, also setup one-to-one mapping for the page that turns on MMU
Initialize TLB, caches, setup MMU to be turned on
Turn on MMUBranch to start_kernel

Execution in C

C entry point – start_kernel() init/main.c
Disable IRQ local_irq_disable()
Print Linux banner
Arch specific setup setup_arch() (arch/arm/kernel/setup.c)
Using mach-id, get pointer to machine_desc (defined in board file)
Using ATAG physical pointer, obtain virtual address
Invoke machine specific fixup
Save & parse ATAGS parse_atags() (arch/arm/kernel/setup.c)
Parse early params parse_early_params
arm_memblock_init (arch/arm/mm/init.c)
Invoke machine specific reserve

Setup pagetables paging_init (arch/arm/mm/mmu.c)
prepare_pagetable
Map memory banks
Map machine vectors devicemaps_init
Invoke machine specific map_io
Allocate zero page
bootmem_init (arch/arm/mm/init.c)

Install vectors early_trap_init (arch/arm/kernel/traps.c)
Invoke machine specific init_early

Build memory zone list build_all_zonelists() (mm/pagealloc.c)
Print Kernel command line
Parse early params
Parse commandline args parse_args (kernel/params.c)
pid hashtable initialization
Setup Kernel memory allocators mm_init
Mark free areas in memory & print memory details
Initialize page cache
Initialize vmalloc

Initialize scheduler sched_init
Disable preemption
Initialize RCU, radix tree
early_irq_init (kernel/irq/irqdesc.c)
Invoke machine specific init_irq
Initialize software timers, soft irq init_timers (kernel/timer.c), softirq_init (kernel/softirq.c)
Initialize clocksource & common timekeeping values timekeeping_init (kernel/time/timekeeping.c)
time_init (arch/arm/kernel/time.c)
Get machine specific timer
Invoke machine specific timer->init
sched_clock post init

Enable IRQ
Initialize console device (if console_initcall) console_init (drivers/tty/tty_io.c)
kmem_leak_init (mm/kmemleak.c)
Allocate per_cpu pagesets setup_per_cpu_pageset (mm/pagealloc.c)
Initialize NUMA policy numa_policy_init (mm/mempolicy.c)
calibrate_delay (init/calibrate.c)
Initialize pid map pidmap_init (kernel/pid.c)
Initialize anonymous vma anon_vma_init (mm/rmap.c)
Initialize init process structure fork_init (kernel/fork.c)
Initialize security framework security_init (security/security.c)
Initialize kdb kdb_init (kernel/debug/kdb/kdb_main.c)
Initialize caches for VFS vfs_caches_init (fs/dcache.c)
Initialize proc FS proc_root_init (fs/proc/root.c)
Initialize ftrace ftrace_init (kernel/trace/ftrace.c)
rest_init (in non-init section)
Spawn init process
Spawn kthreadd
Wait till kthreadd is setup
Enable preemption
schedule schedule (kernel/sched.c)
Disable preemption
cpu_idle (arch/arm/kernel/process.c)

process – 1 (init process) kernel_init (init/main.c)
Wait till kthreadd is setup
do_basic_setup
Create usermode helper wq usermodehelper_init (kernel/kmod.c)
Initialize tmpfs init_tmpfs (mm/shmem.c)
Initialize driver model driver_init (drivers/base/init)
Call initcalls as per the order (machine specific init_machine would get called due to this) do_initcalls

prepare_namespace (init/do_mounts.c)
Load initrd initrd_load (init/do_mounts_initrd.c)
Identify decompressor method identify_ramdisk_image (init/do_mounts_initrd.c)
Create memory for uncompressed FS
Decompress FS and copy crd_load (init/do_mounts_rd)

Mount root FS mount_root (init/do_mounts.c)

init_post (in non-init section)
Free memory in init section free_initmem (arch/arm/mm/init.c)
Replace process – 1 (a kernel thread) with userspace init process, by exec in kernel run_init_process

Credit : Suresh Thiagarajan