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

Eric Saint Etienne
2018-11-23T18:24:49Z

> > + /*
> > + * 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()

-eric