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 <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Jiri Olsa <[email protected]>
---
[v2] added a comment
tools/perf/util/symbol-elf.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index f3577f7d72fe..ecc05aa8399d 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1226,12 +1226,26 @@ 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;
gelf_getshdr(sec, &shdr);
+ /*
+ * We have to fallback to runtime when syms' section header has
+ * NOBITS set. NOBITS results in file offset (sh_offset) not
+ * being incremented. So sh_offset used below has different
+ * values for syms (invalid) and runtime (valid).
+ */
+ 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);
+ }
+
if (is_label && !elf_sec__filter(&shdr, secstrs))
continue;
--
2.30.1
Em Wed, Feb 17, 2021 at 01:21:25PM +0100, Jiri Slaby escreveu:
> 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 <[email protected]>
> Acked-by: Namhyung Kim <[email protected]>
Thanks, applied.
- Arnaldo
> Cc: Peter Zijlstra <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Arnaldo Carvalho de Melo <[email protected]>
> Cc: Mark Rutland <[email protected]>
> Cc: Alexander Shishkin <[email protected]>
> Cc: Jiri Olsa <[email protected]>
> ---
> [v2] added a comment
>
> tools/perf/util/symbol-elf.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index f3577f7d72fe..ecc05aa8399d 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1226,12 +1226,26 @@ 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;
>
> gelf_getshdr(sec, &shdr);
>
> + /*
> + * We have to fallback to runtime when syms' section header has
> + * NOBITS set. NOBITS results in file offset (sh_offset) not
> + * being incremented. So sh_offset used below has different
> + * values for syms (invalid) and runtime (valid).
> + */
> + 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);
> + }
> +
> if (is_label && !elf_sec__filter(&shdr, secstrs))
> continue;
>
> --
> 2.30.1
>
--
- Arnaldo