linux-kernel - Re: [PATCH] Add kernel support for oprofile callgraphs on AVR32

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Message-ID: <20080903130224.251cd97c@hskinnemo-gx745.norway.atmel.com>
Date:	Wed, 3 Sep 2008 13:02:24 +0200
From:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
To:	"Voss, Nikolaus" <N.Voss@...nmann.de>
Cc:	<kernel@...32linux.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add kernel support for oprofile callgraphs on AVR32

"Voss, Nikolaus" <N.Voss@...nmann.de> wrote:
> Hi,
> 
> > Hmm. This appears to be the third backtracer added to avr32, the first
> > two being dump_stack() and friends in arch/avr32/kernel/process.c, and
> > save_stack_trace() in arch/avr32/kernel/stacktrace.c.
> > 
> > Would be nice if some of this could be consolidated.
> 
> I considered using one of them, in fact I also have a version with an
> extended stacktrace.c. But due to the small size of the kernel stacktracer
> (only a few lines), I found it cleaner to create a separate version. The
> overall size is smaller and it cannot potentially mess up other things.
> Cf. e.g. the x86 tracer which is of the generic type, but comparatively big
> and hard to follow through the places.

Good point.

> > > +		/* Assume we have frame pointers in user mode process */
> > 
> > What happens if we don't? I assume it will stop when it detects that
> > the frame pointer isn't monotonically increasing or when it gets a
> > fault?
> 
> Right. This might lead to false information in oprofile, this case is
> described in the oprofile docs. 

Ok.

I've applied it to the avr32 tree along with a couple of trivial
checkpatch fixes. There's one remaining warning:

WARNING: externs should be avoided in .c files
#125: FILE: arch/avr32/oprofile/op_model_avr32.c:25:
+void avr32_backtrace(struct pt_regs * const regs, unsigned int depth);

total: 0 errors, 1 warnings, 102 lines checked

We should probably add a header file somewhere, but I'm too lazy to do
it right now.

Haavard
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