What Run First

Form Arm-Linux Mailing list, posted by Russell King
http://lists.arm.linux.org.uk/lurker/message/20011005.154003.5d698445.html

What runs first depends on what type of kernel you start running.

Compressed kernel (aka zImage):

1. the startup code in arch/arm/boot/compressed/head.S (start label)
   (and maybe some other architecture specific code in other head-*.S files in that directory).
   
2. Decompressor proper (via decompress_kernel) in arch/arm/boot/compressed/misc.c which gunzips the kernel.
   
3. We then relocate the kernel if required, and call it.
   

Uncompressed kernel (aka Image):
This is where we join the uncompressed kernel startup.

4. arch/arm/kernel/head-armv.S (Edit head.S and head-*.S ) describes this, and includes such things as:
   page table initialization and processor cache initialization
   (via support stuff in arch/arm/mm/proc-*.S).
5. We then proceed to start_kernel in init/main.c, and everything follows from that point on.
   
6. The only other thing to note is that the various drivers are initialized via a table built by the linker from the __initcall() and module_init() statements scattered throughout the kernel source. The code which calls them can be found in init/main.c: do_initcalls().