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Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)
- From: Karim Yaghmour <karim at opersys dot com>
- To: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
- Cc: Ingo Molnar <mingo at elte dot hu>, Martin Bligh <mbligh at google dot com>, "Frank Ch. Eigler" <fche at redhat dot com>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, prasanna at in dot ibm dot com, Andrew Morton <akpm at osdl dot org>, 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: Fri, 22 Sep 2006 13:03:21 -0400
- Subject: Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)
- Organization: Opersys inc.
- References: <20060921160009.GA30115@Krystal> <20060921160656.GA24774@elte.hu> <20060921214248.GA10097@Krystal> <20060922070714.GB4167@elte.hu> <20060922150810.GB20839@Krystal> <45140E33.9030509@opersys.com> <20060922161353.GA1569@Krystal>
- Reply-to: karim at opersys dot com
Mathieu Desnoyers wrote:
> First of all, I think that specific architecture-specific optimisations can and
> should be integrated in a more generic portable framework.
No disagreement there. If Ingo would care to comment, I think it might
be an acceptable compromise to have x86 fully use kprobes/djprobes
immediately, and the other archs could walk there at their rate.
Practically, some stuff in include/asm-i386/markers.h and
include/asm-x86_64/markers.h would contain the binary modifiable stuff
and include/asm-generic/markers.h could contain a platform-independent
fallback.
> Hrm, your comment makes me think of an interesting idea :
>
> .align
> jump_address:
> near jump to end
> setup_stack_address:
> setup stack
> call empty function
> end:
>
> So, instead of putting nops in the target area, we fill it with a useful
> function call. Near jump being 2 bytes, it might be much easier to modify.
> If necessary, making sure the instruction is aligned would help to change it
> atomically. If we mark the jump address, the setup stack address and the end
> tag address with symbols, we can easily calculate (portably) the offset of the
> near jump to activate either the setup_stack_address or end tags.
That's another possibility. It seems more C friendly than the simple
short-jump+3bytes.
Ingo?
Karim
--
President / Opersys Inc.
Embedded Linux Training and Expertise
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