http://gicl.cs.drexel.edu/people/sevy/linux/ARM_Linux_boot_sequence.html
ARM Linux Boot Sequence
The following traces the Linux boot sequence for ARM-based systems in
the 2.6.18 kernel. It looks at just the earliest stages of the boot
process, until the generic non-processor-specific start_kernel function
is called. The line numbers of each statement are in parenthese at the
end of the line; the kernel source itself can be conveniently browsed on
the Linux Cross-Reference website.
zImage decompression
* arch/arm/boot/compressed/head.S: start (108)
* First code executed, jumped to by the bootloader, at
label "start" (108)
* save contents of registers r1 and r2 in r7 and r8 to
save off architecture ID and atags pointer passed in by
bootloader (118)
* execute arch-specific code (inserted at 146)
* arch/arm/boot/compressed/head-xscale.S or other
arch-specific code file
* added to build in
arch/arm/boot/compressed/Makefile
* linked into head.S by linker section
declaration: .section "start"
* flush cache, turn off cache and MMU
* load registers with stored parameters (152)
* sp = stack pointer for decompression code (152)
* r4 = zreladdr = kernel entry point physical
address
* check if running at link address, and fix up global
offset table if not (196)
* zero decompression bss (205)
* call cache_on to turn on cache (218)
* defined at arch/arm/boot/compressed/head.S (320)
* call call_cache_fn to turn on cache as
appropriate for processor variant
* defined at
arch/arm/boot/compressed/head.S (505)
* walk through proc_types list (530) until
find corresponding processor
* call cache-on function in list item
corresponding to processor (511)
* for ARMv5tej core, cache_on
function is __armv4_mmu_cache_on
(417)
* call setup_mmu to set up
initial page tables
since MMU must be on for
cache to be on (419)
* turn on cache and MMU
(426)
* check to make sure won't overwrite image during
decompression; assume not for this trace (232)
* call decompress_kernel to decompress kernel to RAM (277)
* branch to call_kernel (278)
* call cache_clean_flush to flush cache contents
to RAM (484)
* call cache_off to turn cache off as expected by
kernel initialization routines (485)
* jump to start of kernel in RAM (489)
* jump to address in r4 = zreladdr from
previous load
* zreladdr = ZRELADDR = zreladdr-y
* zreladdr-y specified in
arch/arm/mach-vx115/Makefile.boot
ARM-specific kernel code
* arch/arm/kernel/head.S: stext (72)
* call __lookup_processor_type (76)
* defined in arch/arm/kernel/head-common.S (146)
* search list of supported processor types
__proc_info_begin (176)
* kernel may be built to support more than
one processor type
* list of proc_info_list structs
* defined in
arch/arm/mm/proc-arm926.S (467)
and other corresponding proc-*.S
files
* linked into list by section
declaration: .section
".proc.info.init"
* return pointer to proc_info_list struct
corresponding to processor if found, or loop in
error if not
* call __lookup_machine_type (79)
* defined in arch/arm/kernel/head-common.S (194)
* search list of supported machines (boards)
* kernel may be built to support more than
one board
* list of machine_desc structs
* machine_desc struct for boards
defined in board-specific file
vx115_vep.c
* linked into list by section
declaration that's part of
MACHINE_DESC macro
* return pointer to machine_desc struct
corresponding to machine (board)
* call __create_page_tables to set up initial MMU tables
(82)
* set lr to __enable_mmu, r13 to address of __switch_data
(91, 93)
* lr and r13 used for jumps after the following
calls
* __switch_data defined in
arch/arm/kernel/head-common.S (15)
* call the __cpu_flush function pointer in the previously
returned proc_info_list struct (94)
* offset is #PROCINFO_INITFUNC into struct
* this function is __arm926_setup for the ARM
926EJ-S, defined in arch/arm/mm/proc-arm926.S
(392)
* initialize caches, writebuffer
* jump to lr, previously set to address of
__enable_mmu
* __enable_mmu (147)
* set page table pointer (TTB) in MMU hardware so
it knows where to start page-table walks (167)
* enable MMU so running with virtual addresses
(185)
* jump to r13, previously set to address of
__switch_data, whose first field is address of
__mmap_switched
* __switch_data defined in
arch/arm/kernel/head-common.S (15)
* arch/arm/kernel/head-common.S: __mmap_switched (35)
* copy data segment to RAM (39)
* zero BSS (45)
* branch to start_kernel (55)
Processor-independent kernel code
* init/main.c: start_kernel (456)
--
Regards,
Peter Teoh
