Re: [PATCH] perf symbols: Cannot disassemble some routines when debuginfo present

Arnaldo Carvalho de Melo
2018-11-27T12:36:00Z

Em Mon, Nov 26, 2018 at 09:39:17AM +0100, Jiri Olsa escreveu:
> On Fri, Nov 23, 2018 at 10:24:21AM -0800, Eric Saint Etienne wrote:
> > > > + /*
> > > > + * 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
> >
> > The split happens in dso_process_kernel_symbol() in symbol-elf.c where we
> > call map_groups__find_by_name() to find an existing map, but with
> > -ffunction-sections and a symbol belonging to new (function) map, such map
> > doesn't exist yet so we end up creating one and adjusting existing maps
> > accordingly because adjust_kernel_syms is set. Makes sense?
> >
> > As of 4.20-rc3 the call chain is as follows:
> > event:c:1573 map__load()
> > map.c:315 dso__load()
> > symobl.c:1528 dso__load_kernel_sym()
> > symbol.c:1896 dso__load_vmlinux_path()
> > (or we directly call dso__load_vmlinux() at line 1892)
> > symbol.c:1744 dso__load_vmlinux()
> > symbol.c:1719 dso__load_sym()
> > symbol-elf.c:1090 dso_process_kernel_symbol()
>
> i see, thank for the pointers.. could you please mention
> this in your comment and changelog as well?
>
> also to document in the code that it's related to map__load
> could you put it to the if contidion, like:
>
> + if (load_map && (al->addr < al->map->start || al->addr >= al->map->end))
>

Eric, please address Jiri's comments and send a v2, ok?

- Arnaldo