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Message-ID: <f86b20530507280922819d927@mail.gmail.com>
Date: Thu, 28 Jul 2005 16:23:00 -0000
From: Masami Hiramatsu <masami.hiramatsu@gmail.com>
Reply-To: Masami Hiramatsu <masami.hiramatsu@gmail.com>
To: karim@opersys.com
Subject: Re: Hitachi djprobe mechanism
Cc: "Keshavamurthy, Anil S" <anil.s.keshavamurthy@intel.com>, 
	Masami Hiramatsu <hiramatu@sdl.hitachi.co.jp>, 
	Roland McGrath <roland@redhat.com>, 
	Richard J Moore <richardj_moore@uk.ibm.com>, 
	SystemTAP <systemtap@sources.redhat.com>, sugita@sdl.hitachi.co.jp, 
	Satoshi Oshima <soshima@redhat.com>
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	 <42E83895.6070602@opersys.com> <42E83CEC.8040702@opersys.com>
X-SW-Source: 2005-q3/txt/msg00145.txt.bz2

Hi,

2005/7/28, Karim Yaghmour <karim@opersys.com>:
> Karim Yaghmour wrote:
> >From the article's text:
> > "The springboard approach requires chunks of scratch space (collectivel=
y,
> > the springboard heap) to be conveniently sprinkled throughout the kerne=
l,
> > so that every kernel instruction can reach some chunk when using one of
> > the suitable instructions ..."
>
> Also, there's this bit I missed from the figure the text refers to as
> containing the list of instructions that can be used for various architec=
tures
> (figure 4.6):
>
> "None of the architectures has an ideal splicing instruction; either
> displacement is insufficient (RISC architectures), or there is no
> guarantee that only a single instruction is overwritten when splicing (x8=
6)."
>
> To the best of my understanding, the latter seems to imply that springboa=
rds
> have the very same limitations mentioned earlier for djprobe.

I think so. the size of smallest jmp instruction is 2 bytes on i386,
but the smallest instruction is 1byte on i386 (ex. pushl %esi).
I will try to add safety check routine in sched() and do_IRQ().

--
Masami Hiramatsu
mailto:masami.hiramatsu@gmail.com