On Fri, Nov 23, 2018 at 02:25:26AM -0800, Eric Saint-Etienne wrote: > When the kernel is compiled with -ffunction-sections and perf uses the > kernel debuginfo, perf fails the very first symbol lookup and ends up with > an hex offset inside [kernel.vmlinux]. It's due to how perf loads the maps. > > Indeed only .text gets loaded by map_groups__find() into al->map. > Consequently al->map address range encompass the whole code. > But map__load() has just loaded many function maps by splitting al->map, > which reduced al->map range drastically. Very likely the target address is > now in one of those newly created function maps, so we need to lookup the > map again to find that new map. > > This issue is not specific to the kernel but to how the image is linked. > For the kernel, when we're not using the kernel debuginfo, perf will > fallback to using kallsyms and then the first lookup will work. > > This patch makes sure that the event address we're looking-up is indeed > within the map we've found, otherwise we lookup another map again. > Only one extra lookup at most is required for the proper map to be found, > if it exists. > > Signed-off-by: Eric Saint-Etienne <eric.saint.etie...@oracle.com> > Reviewed-by: Darren Kenny <darren.ke...@oracle.com> > --- > tools/perf/util/event.c | 23 ++++++++++++++++++++++- > 1 file changed, 22 insertions(+), 1 deletion(-) > > diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c > index e9c108a..a69ef52 100644 > --- a/tools/perf/util/event.c > +++ b/tools/perf/util/event.c > @@ -1571,7 +1571,28 @@ struct map *thread__find_map(struct thread *thread, u8 > cpumode, u64 addr, > */ > if (load_map) > map__load(al->map); > - al->addr = al->map->map_ip(al->map, al->addr); > + > + /* > + * When using -ffunction-sections, only .text gets loaded by > + * map_groups__find() into al->map. Consequently al->map address > + * range encompass the whole code. > + * > + * But map__load() has just loaded many function maps by > + * splitting al->map, which reduced al->map range drastically. > + * Very likely the target address is now in one of those newly > + * created function maps, so we need to lookup the map again > + * to find that new map. > + */
hum, so map__load actualy can split the map to create new maps? cold you please point me to that code? I haven't touch this area for some time and I can't find it thanks, jirka > + if (al->addr < al->map->start || al->addr >= al->map->end) > + al->map = map_groups__find(mg, al->addr); > + > + /* > + * The new map *ought* to exist because the initial al->map > + * contained that address and subsequently has been split into > + * many *contiguous* maps. > + */ > + if (al->map != NULL) > + al->addr = al->map->map_ip(al->map, al->addr); > } > > return al->map; > -- > 1.8.3.1 >
