when does "init" become usermode process

when does "init" become usermode process

[shenminshi]

Hi,
  I was reading the kernel boot code toward the end where kernel's init thread execve("/sbin/init",x,x). Execve() calls sys_execve() and do_execve(). All the manpage and kernel document told us the init is the first usermode process running in the system. However, when the execve("/sbin/init",x,x) runs in the kernel (init/main.c), I believe we are still in the kernel mode, aren't we? Unless execve() does the trick to turn init into usermode by setting the KU bit in the STATUS register. I checked the execve() code and its not obvious whether it does this or not. I then check the init source code and it does not mess around the KU bit either.

My question is when and how does init turn itself into usermode.


Thanks

sms

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Re: when does "init" become usermode process

[Kip Walker]

shenminshi@netscape.net wrote:
> 
> My question is when and how does init turn itself into usermode.

Look at 'start_thread' in arch/mips/kernel/process.c, which is called
from load_elf_binary in fs/binfmt_elf.c (as a result of the execve
syscall).

Kip