perf symbols: Add support for 'variable' symtabs

Example:

{
	u64 addr = strtoull(sym_filter, NULL, 16);
	struct map *map = map_groups__find(kmaps, MAP__VARIABLE, addr);

	if (map == NULL)
		pr_err("couldn't find map!\n");
	else {
		struct symbol *sym = map__find_symbol(map, addr, NULL);
		if (sym == NULL)
			pr_err("couldn't find addr!\n");
		else
			pr_info("addr %#Lx is in %s global var\n", addr, sym->name);
	}
	exit(0);
}

Added just after symbol__init() call in 'perf top', then:

{
        u64 addr = strtoull(sym_filter, NULL, 16);
        struct map *map = map_groups__find(kmaps, MAP__VARIABLE, addr);

        if (map == NULL)
                pr_err("couldn't find map!\n");
        else {
                struct symbol *sym = map__find_symbol(map, addr, NULL);
                if (sym == NULL)
                        pr_err("couldn't find addr!\n");
                else
                        pr_info("addr %#Lx is in %s global var\n", addr, sym->name);
        }
        exit(0);
}

[root@doppio linux-2.6-tip]# grep ' [dD] ' /proc/kallsyms | grep ' sched'
ffffffff817827d8 d sched_nr_latency
ffffffff81782ce0 d sched_domains_mutex
ffffffff8178c070 d schedstr.22423
ffffffff817909a0 d sched_register_mutex
ffffffff81823490 d sched_feat_names
ffffffff81823558 d scheduler_running
ffffffff818235b8 d sched_clock_running
ffffffff818235bc D sched_clock_stable
ffffffff81824f00 d sched_switch_trace
[root@doppio linux-2.6-tip]# perf top -s 0xffffffff817827d9
addr 0xffffffff817827d9 is in sched_nr_latency global var
[root@doppio linux-2.6-tip]# perf top -s ffffffff81782ce0
addr 0xffffffff81782ce0 is in sched_domains_mutex global var
[root@doppio linux-2.6-tip]#
[root@doppio linux-2.6-tip]# perf top -s ffffffff81782ce0 --vmlinux OFF
The file OFF cannot be used, trying to use /proc/kallsyms...addr 0xffffffff81782ce0 is in sched_domains_mutex global var
[root@doppio linux-2.6-tip]# perf top -s ffffffff818235bc --vmlinux OFF
The file OFF cannot be used, trying to use /proc/kallsyms...addr 0xffffffff818235bc is in sched_clock_stable global var
[root@doppio linux-2.6-tip]#

So it works with both /proc/kallsyms and with ELF symtabs, either
the one on the vmlinux explicitely passed via --vmlinux or in one
in the vmlinux_path that matches the buildid for the running kernel
or the one found in the buildid header section in a perf.data file.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1260550239-5372-4-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>