* What's the value of %cs before jump in pm32 on booting? @ 2011-08-11 11:18 jiangtao.jit 2011-08-11 14:53 ` Mulyadi Santosa 0 siblings, 1 reply; 3+ messages in thread From: jiangtao.jit @ 2011-08-11 11:18 UTC (permalink / raw) To: kernelnewbies Hi all: on booting of x86 top of file arch/x86/boot/pmjump.S there is code ------------------- GLOBAL(protected_mode_jump) movl %edx, %esi xorl %ebx, %ebx movw %cs, %bx shll $4, %ebx addl %ebx, 2f ... ------------------- what's the value of %cs here? how was it loaded? i would really appreciate if someone provide me some references thank you very much 2011-08-11 jiangtao.jit ^ permalink raw reply [flat|nested] 3+ messages in thread
* What's the value of %cs before jump in pm32 on booting? 2011-08-11 11:18 What's the value of %cs before jump in pm32 on booting? jiangtao.jit @ 2011-08-11 14:53 ` Mulyadi Santosa 2011-08-11 16:29 ` Jonathan Neuschäfer 0 siblings, 1 reply; 3+ messages in thread From: Mulyadi Santosa @ 2011-08-11 14:53 UTC (permalink / raw) To: kernelnewbies On Thu, Aug 11, 2011 at 18:18, jiangtao.jit <jiangtao.jit@gmail.com> wrote: > Hi all: > > on booting of x86 > top of file arch/x86/boot/pmjump.S > there is code > ------------------- > GLOBAL(protected_mode_jump) > ? ? ? ?movl ? ?%edx, %esi > ? ? ? ?xorl ? ?%ebx, %ebx i think it's zeroing bx (l--> low I suppose) > ? ? ? ?movw ? ?%cs, %bx then, it should zero the content of cs. Quite likely, it means to jump to cpu ring level 0 and do something there.. -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com ^ permalink raw reply [flat|nested] 3+ messages in thread
* What's the value of %cs before jump in pm32 on booting? 2011-08-11 14:53 ` Mulyadi Santosa @ 2011-08-11 16:29 ` Jonathan Neuschäfer 0 siblings, 0 replies; 3+ messages in thread From: Jonathan Neuschäfer @ 2011-08-11 16:29 UTC (permalink / raw) To: kernelnewbies On Thu, Aug 11, 2011 at 09:53:10PM +0700, Mulyadi Santosa wrote: > On Thu, Aug 11, 2011 at 18:18, jiangtao.jit <jiangtao.jit@gmail.com> wrote: > > Hi all: > > > > on booting of x86 > > top of file arch/x86/boot/pmjump.S > > there is code > > ------------------- > > GLOBAL(protected_mode_jump) > > ? ? ? ?movl ? ?%edx, %esi > > ? ? ? ?xorl ? ?%ebx, %ebx > > i think it's zeroing bx (l--> low I suppose) Long, actually, i.e. 32-bit. > > > ? ? ? ?movw ? ?%cs, %bx > > then, it should zero the content of cs. Quite likely, it means to jump > to cpu ring level 0 and do something there.. No, this is written in AT&T syntax, where the source comes first, and then the destination. IOW, the code means: Copy the 16 bit register CS into the lower 16 bit of EBX (which is BX). CMIIW, Jonathan Neusch?fer ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2011-08-11 16:29 UTC | newest] Thread overview: 3+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2011-08-11 11:18 What's the value of %cs before jump in pm32 on booting? jiangtao.jit 2011-08-11 14:53 ` Mulyadi Santosa 2011-08-11 16:29 ` Jonathan Neuschäfer
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