linux-kernel - Re: [PATCH 4/4] perf tools: Add support for breakpoint events in perf tools

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Date:	Mon, 23 Nov 2009 22:25:01 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 4/4] perf tools: Add support for breakpoint events in
 perf tools


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> > Using just /proc/kallsyms all we can do is find the size of a 
> > variable by looking at its address and the address of the next one.
> > 
> > - Arnaldo
> 
> Hmm, but I worry a bit about alignment which would return us the wrong 
> size.
> 
> May be can we first try to get the address from /proc/kallsyms, and if 
> we have dwarf, get the size from it, otherwise try some magic with 
> /proc/kallsysms...

Can we extend /proc/kallsyms (or add /proc/kallsyms) to include a size 
field?

Perhaps can we generate some sort of DSO-alike thing in /proc/vmlinux 
(via a default-off debug option in .config), that perf could just 
interpret the usual ELF way - which happens to be the symbol table of 
the kernel? It would use up some RAM, but it would also be quite useful 
for debugging purposes.

	Ingo
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