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Re: [RFC][PATCH 0/4][kprobe](djprobe) Direct jump optimized kprobes
- From: Satoshi Oshima <soshima at redhat dot com>
- To: "Frank Ch. Eigler" <fche at redhat dot com>, Ingo Molnar <mingo at redhat dot com>
- Cc: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, "Keshavamurthy, Anil S" <anil dot s dot keshavamurthy at intel dot com>, SystemTAP <systemtap at sources dot redhat dot com>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Prasanna S Panchamukhi <prasanna at in dot ibm dot com>, Hideo Aoki <haoki at redhat dot com>, Yumiko Sugita <yumiko dot sugita dot yf at hitachi dot com>, Jim Keniston <jkenisto at us dot ibm dot com>, Martin Bligh <mbligh at google dot com>, Greg Kroah-Hartman <gregkh at suse dot de>
- Date: Mon, 27 Nov 2006 19:05:31 -0500
- Subject: Re: [RFC][PATCH 0/4][kprobe](djprobe) Direct jump optimized kprobes
- References: <4562A150.2030606@hitachi.com> <1164632388.22536.109.camel@earth> <y0my7pwplqf.fsf@ton.toronto.redhat.com>
Frank Ch. Eigler wrote:
> mingo wrote:
>
>> [...] I'm wondering whether it could be made a 100% transparent
>> speedup to kprobes: how hard would it be to do a simplified
>> disassembly of the target address to automate the 'this kprobe can
>> safely be turned into a djprobe transparently' step [...]
>
> The entire criterion is not easy to check at the binary point. In
> particular, it is hard to tell whether some part of the overlaid
> instruction sequence is the possible target of a branch elsewhere.
Yes. This is the problem. We couldn't find anything good way to
ensure the safety of branch target without debuginfo.
Now we are developing safety check tool that bases on
elfutils.
And during this safety check process, userspace tool must count
the length of replaced instructions. So we chose the length as
a trigger to enable djprobes. It is not the problem to count
the length of instructions inside kernel.
If you have any suggestion on this, we appreciate them.
Satoshi