Thuc notes - Linux kernel boot process
Part of series osdev |
- BIOS loads Linux Kernel to memory and split to 2 parts:
- Real-mode kernel: Below 640K of memory
- Proctected-mode kernel: Start from 1MB of memory
Real-mode kernel:
http://lxr.linux.no/#linux+v2.6.25.6/arch/x86/boot/header.S#L110
- Real-mode kernel will be start by BIOS at
_start:
- It will jump directly to
start_of_setup:
- Real-mode kernel will be start by BIOS at
http://lxr.linux.no/#linux+v2.6.25.6/arch/x86/boot/header.S#L229
_start
jumps tostart_of_setup:
- Reset disk controller
- Setup stack
- Zero bss (https://en.wikipedia.org/wiki/.bss)
- Call to a C
main()
http://lxr.linux.no/#linux+v2.6.25.6/arch/x86/boot/main.c#L122
start_of_setup:
callsmain()
- Prepare/copy boot parameters
- Initilize memory heap
- Detect memory layout
- Query MCA
- Set video mode
- Invoke method
go_to_protected_mode()
http://lxr.linux.no/#linux+v2.6.25.6/arch/x86/boot/pm.c#L153
main()
callsgo_to_protected_mode()
- The method purpose is used to prepare steps before switch to protected mode
- Switch hook
- Move compressed kernel to correct place
- Resejt co-processors
- Setup IDT https://en.wikipedia.org/wiki/Interrupt_descriptor_table
- Setup GDT https://en.wikipedia.org/wiki/Global_Descriptor_Table
- Jump to
protected_mode_jump:
Protected-mode:
http://lxr.linux.no/#linux+v2.6.25.6/arch/x86/boot/pmjump.S#L31
go_to_protected_mode()
callsprotected_mode_jump:
- Prepare/copy boot parameters
- Enable protected mode
- Disable paging https://en.wikipedia.org/wiki/Memory_paging
- Jump to
startup_32:
http://lxr.linux.no/#linux+v2.6.25.6/arch/x86/boot/compressed/head_32.S#L35
protected_mode_jump:
jumps tostartup_32:
- Doing some stuffs
- Call to
decompress_kernel()
- Clears the bss segment
- Setup final GDT https://en.wikipedia.org/wiki/Global_Descriptor_Table
- Enables paging https://en.wikipedia.org/wiki/Memory_paging
- Initializes a stack
- Setup final IDT https://en.wikipedia.org/wiki/Interrupt_descriptor_table
- Call to
start_kernel()
http://lxr.linux.no/#linux+v2.6.25.6/arch/x86/boot/compressed/misc.c#L368
startup_32:
calls todecompress_kernel()
- Uncompressed kernel will replace at place of existed compressed kernel. Start at 1MB
http://lxr.linux.no/#linux+v2.6.25.6/init/main.c#L507
startup_32:
calls tostart_kernel()
- Set PID = 0
- Initialize stuffs, such as: scheduler, memory zones, time keeping, cpu, cgroup
- Call to
rest_init()
http://lxr.linux.no/#linux+v2.6.25.6/init/main.c#L432
start_kernel()
calls torest_init()
- Create another thread to call
kernel_init()
- Create scheduling
- Sleep by call
cpu_idle()
http://lxr.linux.no/linux+v2.6.25.6/init/main.c#L808
start_kernel()
create thread and call tokernel_init()
- Set PID = 1
- Init the remaining CPUs
- Init work queue
- Init user mode
- Init driver
- Call to
init_post()
http://lxr.linux.no/#linux+v2.6.25.6/init/main.c#L769
kernel_init()
calls toinit_post()
- Execute /sbin/init, /etc/init, /bin/init, and /bin/sh in order