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Re: Hitachi djprobe mechanism
- From: Masami Hiramatsu <masami dot hiramatsu at gmail dot com>
- To: karim at opersys dot com
- Cc: "Keshavamurthy, Anil S" <anil dot s dot keshavamurthy at intel dot com>, Masami Hiramatsu <hiramatu at sdl dot hitachi dot co dot jp>, Roland McGrath <roland at redhat dot com>, Richard J Moore <richardj_moore at uk dot ibm dot com>, SystemTAP <systemtap at sources dot redhat dot com>, sugita at sdl dot hitachi dot co dot jp, Satoshi Oshima <soshima at redhat dot com>
- Date: Fri, 29 Jul 2005 01:22:46 +0900
- Subject: Re: Hitachi djprobe mechanism
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- References: <44BDAFB888F59F408FAE3CC35AB4704101E506F6@orsmsx409> <42E83895.6070602@opersys.com> <42E83CEC.8040702@opersys.com>
- Reply-to: Masami Hiramatsu <masami dot hiramatsu at gmail dot com>
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 (collectively,
> > the springboard heap) to be conveniently sprinkled throughout the kernel,
> > 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 architectures
> (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 (x86)."
>
> To the best of my understanding, the latter seems to imply that springboards
> 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