linux-kernel - Re: [PATCH V2 8/9] perf tools: Adjust kallsyms for relocated kernel

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Date:	Wed, 29 Jan 2014 16:08:50 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH V2 8/9] perf tools: Adjust kallsyms for relocated kernel

Em Wed, Jan 29, 2014 at 04:14:43PM +0200, Adrian Hunter escreveu:
> If the kernel is relocated at boot time, kallsyms
> will not match data recorded previously.  That
> does not matter for modules because they are
> corrected anyway.  It also does not matter if
> vmlinux is being used for symbols. But if perf
> tools has only kallsyms then the symbols will not
> match.  Fix by applying the delta gained by
> comparing the old and current addresses of the
> relocation reference symbol.

Don't we have map->reloc? Can't we use it here, i.e. be consistent and
have the unrelocated address + the relocation, and then, when using
map->{map,unmap} take that into account, as you did to the objdump
variants, no?

I applied the others, testing now.

- Arnaldo
 
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
>  tools/perf/util/symbol.c | 40 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 4ac1f87..a9d758a 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -627,7 +627,7 @@ static int dso__split_kallsyms_for_kcore(struct dso *dso, struct map *map,
>   * kernel range is broken in several maps, named [kernel].N, as we don't have
>   * the original ELF section names vmlinux have.
>   */
> -static int dso__split_kallsyms(struct dso *dso, struct map *map,
> +static int dso__split_kallsyms(struct dso *dso, struct map *map, u64 delta,
>  			       symbol_filter_t filter)
>  {
>  	struct map_groups *kmaps = map__kmap(map)->kmaps;
> @@ -692,6 +692,12 @@ static int dso__split_kallsyms(struct dso *dso, struct map *map,
>  			char dso_name[PATH_MAX];
>  			struct dso *ndso;
>  
> +			if (delta) {
> +				/* Kernel was relocated at boot time */
> +				pos->start -= delta;
> +				pos->end -= delta;
> +			}
> +
>  			if (count == 0) {
>  				curr_map = map;
>  				goto filter_symbol;
> @@ -721,6 +727,10 @@ static int dso__split_kallsyms(struct dso *dso, struct map *map,
>  			curr_map->map_ip = curr_map->unmap_ip = identity__map_ip;
>  			map_groups__insert(kmaps, curr_map);
>  			++kernel_range;
> +		} else if (delta) {
> +			/* Kernel was relocated at boot time */
> +			pos->start -= delta;
> +			pos->end -= delta;
>  		}
>  filter_symbol:
>  		if (filter && filter(curr_map, pos)) {
> @@ -1130,15 +1140,41 @@ out_err:
>  	return -EINVAL;
>  }
>  
> +/*
> + * If the kernel is relocated at boot time, kallsyms won't match.  Compute the
> + * delta based on the relocation reference symbol.
> + */
> +static int kallsyms__delta(struct map *map, const char *filename, u64 *delta)
> +{
> +	struct kmap *kmap = map__kmap(map);
> +	u64 addr;
> +
> +	if (!kmap->ref_reloc_sym || !kmap->ref_reloc_sym->name)
> +		return 0;
> +
> +	addr = kallsyms__get_function_start(filename,
> +					    kmap->ref_reloc_sym->name);
> +	if (!addr)
> +		return -1;
> +
> +	*delta = addr - kmap->ref_reloc_sym->addr;
> +	return 0;
> +}
> +
>  int dso__load_kallsyms(struct dso *dso, const char *filename,
>  		       struct map *map, symbol_filter_t filter)
>  {
> +	u64 delta = 0;
> +
>  	if (symbol__restricted_filename(filename, "/proc/kallsyms"))
>  		return -1;
>  
>  	if (dso__load_all_kallsyms(dso, filename, map) < 0)
>  		return -1;
>  
> +	if (kallsyms__delta(map, filename, &delta))
> +		return -1;
> +
>  	symbols__fixup_duplicate(&dso->symbols[map->type]);
>  	symbols__fixup_end(&dso->symbols[map->type]);
>  
> @@ -1150,7 +1186,7 @@ int dso__load_kallsyms(struct dso *dso, const char *filename,
>  	if (!dso__load_kcore(dso, map, filename))
>  		return dso__split_kallsyms_for_kcore(dso, map, filter);
>  	else
> -		return dso__split_kallsyms(dso, map, filter);
> +		return dso__split_kallsyms(dso, map, delta, filter);
>  }
>  
>  static int dso__load_perf_map(struct dso *dso, struct map *map,
> -- 
> 1.7.11.7
--
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