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Re: [PATCH] Linux Kernel Markers
- From: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
- To: Vara Prasad <prasadav at us dot ibm 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>, 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: Tue, 19 Sep 2006 15:16:52 -0400
- Subject: Re: [PATCH] Linux Kernel Markers
- References: <20060918234502.GA197@Krystal> <20060919081124.GA30394@elte.hu> <451008AC.6030006@google.com> <20060919154612.GU3951@redhat.com> <4510151B.5070304@google.com> <20060919093935.4ddcefc3.akpm@osdl.org> <45101DBA.7000901@google.com> <20060919063821.GB23836@in.ibm.com> <45102641.7000101@google.com> <4510413F.2030200@us.ibm.com>
* Vara Prasad (prasadav@us.ibm.com) wrote:
> Martin Bligh wrote:
>
> >[...]
> >Depends what we're trying to fix. I was trying to fix two things:
> >
> >1. Flexibility - kprobes seem unable to access all local variables etc
> >easily, and go anywhere inside the function. Plus keeping low overhead
> >for doing things like keeping counters in a function (see previous
> >example I mentioned for counting pages in shrink_list).
> >
> Using tools like systemtap on can consult DWARF information and put
> probes in the middle of the function and access local variables as well,
> that is not the real problem. The issue here is compiler doesn't seem to
> generate required DWARF information in some cases due to optimizations.
> The other related problem is when there exists debug information, the
> way to specify the breakpoint location is using line number which is not
> maintainable, having a marker solves this problem as well. Your proposal
> still doesn't solve the need for markers if i understood correctly.
>
His implementation makes a heavy use of a marker mechanism : this is exactly
what permits to create the instrumented objects from the same source code, but
with different #defines.
Mathieu
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