Messages in this thread Patch in this message | | | From | Jiri Slaby <> | Subject | [PATCH v2] perf tools: Resolve symbols against debug file first | Date | Wed, 17 Feb 2021 13:21:25 +0100 |
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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 <jslaby@suse.cz> Acked-by: Namhyung Kim <namhyung@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> --- [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
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