On Wed, Jan 13, 2021 at 09:01:28AM +0100, Jiri Slaby wrote:
> With LTO, there are symbols like these:
> /usr/lib/debug/usr/lib64/libantlr4-runtime.so.4.8-4.8-1.4.x86_64.debug
> 10305: 0000000000955fa4 0 NOTYPE LOCAL DEFAULT 29
> Predicate.cpp.2bc410e7
>
> This comes from a runtime/debug split done by the standard way:
> objcopy --only-keep-debug $runtime $debug
> objcopy --add-gnu-debuglink=$debugfn -R .comment -R .GCC.command.line
> --strip-all $runtime
>
> perf currently cannot resolve such symbols (relicts of LTO), as section
> 29 exists only in the debug file (29 is .debug_info). And perf resolves
> symbols only against runtime file. This results in all symbols from such
> a library being unresolved:
> 0.38% main2 libantlr4-runtime.so.4.8 [.] 0x00000000000671e0
>
> So try resolving against the debug file first. And only if it fails (the
> section has NOBITS set), try runtime file. We can do this, as "objcopy
> --only-keep-debug" per documentation preserves all sections, but clears
> data of some of them (the runtime ones) and marks them as NOBITS.
>
> The correct result is now:
> 0.38% main2 libantlr4-runtime.so.4.8 [.]
> antlr4::IntStream::~IntStream
>
> Note that these LTO symbols are properly skipped anyway as they belong
> neither to *text* nor to *data* (is_label && !elf_sec__filter(&shdr,
> secstrs) is true).
>
> Signed-off-by: Jiri Slaby <jsl...@suse.cz>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
> Cc: Mark Rutland <mark.rutl...@arm.com>
> Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
> Cc: Jiri Olsa <jo...@redhat.com>
> Cc: Namhyung Kim <namhy...@kernel.org>
> ---
> tools/perf/util/symbol-elf.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index f3577f7d72fe..a31b716fa61c 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1226,12 +1226,20 @@ int dso__load_sym(struct dso *dso, struct map *map,
> struct symsrc *syms_ss,
> if (sym.st_shndx == SHN_ABS)
> continue;
>
> - sec = elf_getscn(runtime_ss->elf, sym.st_shndx);
> + sec = elf_getscn(syms_ss->elf, sym.st_shndx);
> if (!sec)
> goto out_elf_end;
we iterate symbols from syms_ss, so the fix seems to be correct
to call elf_getscn on syms_ss, not on runtime_ss as we do now
I'd think this worked only when runtime_ss == syms_ss
>
> gelf_getshdr(sec, &shdr);
>
> + if (shdr.sh_type == SHT_NOBITS) {
> + sec = elf_getscn(runtime_ss->elf, sym.st_shndx);
> + if (!sec)
> + goto out_elf_end;
> +
> + gelf_getshdr(sec, &shdr);
> + }
is that fallback necessary? the symbol is from syms_ss
Namhyung, any idea?
thanks,
jirka
