Re: [PATCH/RFC 6/9] perf symbols: Use already loaded module dso when loading kcore

[Namhyung Kim]

On Fri, Jun 23, 2017 at 10:55:47AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Jun 23, 2017 at 02:48:24PM +0900, Namhyung Kim escreveu:
> > Even every module has loaded onto same addresses, some modules can be
> > changed and reloaded.
> 
> Can you rephrase the above statement?
> 
> You mean even if a module is reloaded at the same address it can have a
> different symtab and thus misresolve symbols if we get a sample for one
> module version and try to resolve symbols using a symtab for another
> module version?

Right, as I said in other thread, the module can be unloaded, modified
and reloaded between "perf record" and "perf report".


> 
> > In that case it needs to access to the old module
> > in the build-id cache.
> 
> Right, we need to make sure that during a 'perf record' session a mÃdule
> isn't reloaded, because at 'perf record' exit we will record that module
> build-id in a perf.data header and grab a copy (or a hardlink, if
> possible) into the ~/.debug build-id cache, then, at 'perf report' time
> we will read that build-id perf.data table and lookup in the build-id
> cache to get the matching symtab (and full elf .ko file to do things
> like annotation).

That's the desired behavior.  But "perf report" didn't use modules in
the build-id cache when it used kcore (and kallsyms).

Thanks,
Namhyung


>  
> > Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> > Cc: Wang Nan <wangnan0@xxxxxxxxxx>
> > Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> > ---
> >  tools/perf/util/symbol.c | 45 +++++++++++++++++++++++----------------------
> >  1 file changed, 23 insertions(+), 22 deletions(-)
> > 
> > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> > index ce79a51f25bf..fe46eb782297 100644
> > --- a/tools/perf/util/symbol.c
> > +++ b/tools/perf/util/symbol.c
> > @@ -1155,6 +1155,7 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
> >  	int err, fd;
> >  	char kcore_filename[PATH_MAX];
> >  	struct symbol *sym;
> > +	struct map_groups old_mg;
> >  
> >  	if (!kmaps)
> >  		return -EINVAL;
> > @@ -1196,15 +1197,8 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
> >  		goto out_err;
> >  	}
> >  
> > -	/* Remove old maps */
> > -	old_map = map_groups__first(kmaps, map->type);
> > -	while (old_map) {
> > -		struct map *next = map_groups__next(old_map);
> > -
> > -		if (old_map != map)
> > -			map_groups__remove(kmaps, old_map);
> > -		old_map = next;
> > -	}
> > +	old_mg = *kmaps;
> > +	kmaps->maps[map->type].entries = RB_ROOT;
> >  
> >  	/* Find the kernel map using the first symbol */
> >  	sym = dso__first_symbol(dso, map->type);
> > @@ -1223,24 +1217,31 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
> >  	while (!list_empty(&md.maps)) {
> >  		new_map = list_entry(md.maps.next, struct map, node);
> >  		list_del_init(&new_map->node);
> > -		if (new_map == replacement_map) {
> > -			map->start	= new_map->start;
> > -			map->end	= new_map->end;
> > -			map->pgoff	= new_map->pgoff;
> > -			map->map_ip	= new_map->map_ip;
> > -			map->unmap_ip	= new_map->unmap_ip;
> > -			/* Ensure maps are correctly ordered */
> > -			map__get(map);
> > -			map_groups__remove(kmaps, map);
> > -			map_groups__insert(kmaps, map);
> > -			map__put(map);
> > -		} else {
> > -			map_groups__insert(kmaps, new_map);
> > +
> > +		map_groups__insert(kmaps, new_map);
> > +
> > +		if (new_map != replacement_map) {
> > +			old_map = map_groups__find(&old_mg, new_map->type, new_map->start);
> > +			if (old_map && dso__loaded(old_map->dso, old_map->type)) {
> > +				new_map->pgoff = old_map->pgoff;
> > +
> > +				dso__put(new_map->dso);
> > +				new_map->dso = dso__get(old_map->dso);
> > +			}
> >  		}
> >  
> >  		map__put(new_map);
> >  	}
> >  
> > +	/* Remove old maps */
> > +	old_map = map_groups__first(&old_mg, map->type);
> > +	while (old_map) {
> > +		struct map *next = map_groups__next(old_map);
> > +
> > +		map_groups__remove(&old_mg, old_map);
> > +		old_map = next;
> > +	}
> > +
> >  	/*
> >  	 * Set the data type and long name so that kcore can be read via
> >  	 * dso__data_read_addr().
> > -- 
> > 2.13.1