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Re: [PATCH] Linux Kernel Markers
- From: Karim Yaghmour <karim at opersys dot com>
- To: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- Cc: Martin Bligh <mbligh at google dot com>, prasanna at in dot ibm dot com, Andrew Morton <akpm at osdl dot org>, "Frank Ch. Eigler" <fche at redhat dot com>, Ingo Molnar <mingo at elte dot hu>, Mathieu Desnoyers <mathieu dot desnoyers at polymtl dot ca>, Paul Mundt <lethal at linux-sh dot org>, linux-kernel <linux-kernel at vger dot kernel dot org>, Jes Sorensen <jes at sgi dot com>, Tom Zanussi <zanussi at us dot ibm dot com>, Richard J Moore <richardj_moore at uk dot ibm dot com>, Michel Dagenais <michel dot dagenais at polymtl dot ca>, Christoph Hellwig <hch at infradead dot org>, Greg Kroah-Hartman <gregkh at suse dot de>, Thomas Gleixner <tglx at linutronix dot de>, William Cohen <wcohen at redhat dot com>, ltt-dev at shafik dot org, systemtap at sources dot redhat dot com, Alan Cox <alan at lxorguk dot ukuu dot org dot uk>
- Date: Wed, 20 Sep 2006 13:21:52 -0400
- Subject: Re: [PATCH] Linux Kernel Markers
- Organization: Opersys inc.
- References: <20060918234502.GA197@Krystal> <20060919081124.GA30394@elte.hu> <451008AC.firstname.lastname@example.org> <20060919154612.GU3951@redhat.com> <4510151B.email@example.com> <firstname.lastname@example.org> <45101DBA.email@example.com> <20060919063821.GB23836@in.ibm.com> <firstname.lastname@example.org> <20060919070516.GD23836@in.ibm.com> <451030A6.email@example.com> <45105B5E.firstname.lastname@example.org> <451141B1.email@example.com>
- Reply-to: karim at opersys dot com
Masami Hiramatsu wrote:
> This method is very similar to the djprobe.
> And I had gotten the same idea to support preemptive kernel.
> This means the below code, doesn't this?
> jmp 1f /* short jump consumes 2 bytes */
Actually this is slightly different (and requires more support
on behalf of the underlying mechanism then what I was suggesting.)
Basically, as was discussed elsewhere, there is some complex
mechanisms required for taking care of the case where you got
an interrupt at, say, the second or third nop. With the
mechanism I'm suggesting (replacing a 5 byte jmp with a 5 byte
jmp), the underlying mechanics do not require having to take
care of the above-mentioned case.
> - Serialize all processor's cache by using IPI and cpuid.
> I think the djprobe can provide most of functionalities which
> your idea requires.
> I'll update the djprobe against for 2.6.17 or later as soon as
> possible. Would you try to use it?
Basically I'm trying to come up with a mechanism that will be
relatively trivial to implement on any architecture. My
understanding is that kprobes/djprobes combo do not necessarily
fit this description. Of course, that's not a justification for
not trying to get it to work, but my understanding is that
Martin's proposal, if it were implemented, would have a number
of advantages over just having kprobes/djprobes.
Though, in fact, djprobes can be used on the x86 (since it
already works on that) for doing exactly what I'm looking
for: replacing a 5 byte jmp with a 5 byte jmp. My understanding
is that djprobes doesn't need any special intelligence (even
on preemptable kernels) here since it shouldn't need to worry
about an IP back anywhere inside a series of nops. IOW, we
should be able to do what Martin suggests fairly easily (if
we agree on a 5-byte "null" jump at the entry of functions
of interest). Right?