linux-kernel - Re: [tip:perf/urgent] perf symbols: Allow lookups by symbol name too

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Message-ID: <20091215021201.GB6048@nowhere>
Date:	Tue, 15 Dec 2009 03:12:03 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	mingo@...hat.com, hpa@...or.com, acme@...hat.com, paulus@...ba.org,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	efault@....de, tglx@...utronix.de, mhiramat@...hat.com,
	mingo@...e.hu
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf symbols: Allow lookups by symbol name
	too

On Sat, Dec 12, 2009 at 07:22:03AM +0000, tip-bot for Arnaldo Carvalho de Melo wrote:
> Commit-ID:  79406cd789f745ac6aa9d597895f904a98a14007
> Gitweb:     http://git.kernel.org/tip/79406cd789f745ac6aa9d597895f904a98a14007
> Author:     Arnaldo Carvalho de Melo <acme@...hat.com>
> AuthorDate: Fri, 11 Dec 2009 18:50:22 -0200
> Committer:  Ingo Molnar <mingo@...e.hu>
> CommitDate: Sat, 12 Dec 2009 07:42:11 +0100
> 
> perf symbols: Allow lookups by symbol name too
> 
> Configurable via symbol_conf.sort_by_name, so that the cost of an
> extra rb_node on all 'struct symbol' instances is not paid by tools
> that only want to decode addresses.
> 
> How to use it:
> 
> 	symbol_conf.sort_by_name = true;
> 	symbol_init(&symbol_conf);
> 
> 	struct map *map = map_groups__find_by_name(kmaps, MAP__VARIABLE, "[kernel.kallsyms]");
> 
> 	if (map == NULL) {
> 		pr_err("couldn't find map!\n");
> 		kernel_maps__fprintf(stdout);
> 	} else {
> 		struct symbol *sym = map__find_symbol_by_name(map, sym_filter, NULL);
> 		if (sym == NULL)
> 			pr_err("couldn't find symbol %s!\n", sym_filter);
> 		else
> 			pr_info("symbol %s: %#Lx-%#Lx \n", sym_filter, sym->start, sym->end);
> 	}
> 
> Looking over the vmlinux/kallsyms is common enough that I'll add a
> variable to the upcoming struct perf_session to avoid the need to
> use map_groups__find_by_name to get the main vmlinux/kallsyms map.
> 
> The above example looks on the 'variable' symtab, but it is just
> like that for the functions one.
> 
> Also the sort operation is done when we first use
> map__find_symbol_by_name, in a lazy way.



It would be nice to also have a kernel symbol resolution
helper independant of any session.

The problem is that I need to resolve a kernel variable symbol
very early, when we parse record options. We don't have any
session at this time so I can't retrieve the kmaps.

I'm not sure what's the proper way to handle that.

Thanks.

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