perf symbol: Skip symbols if SHF_ALLOC flag is not set

Some symbols are observed with the 'st_value' field zeroed.  E.g.
libc.so.6 in Ubuntu contains a symbol '__evoke_link_warning_getwd' which
resides in the '.gnu.warning.getwd' section.

Unlike normal sections, such kind of sections are used for linker
warning when a file calls deprecated functions, but they are not part of
memory images, the symbols in these sections should be dropped.

This patch checks the section attribute SHF_ALLOC bit, if the bit is not
set, it skips symbols to avoid spurious ones.

Suggested-by: Fangrui Song <maskray@google.com>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Chang Rui <changruinj@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220724060013.171050-3-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index ef6ced5..b3be5b1 100644 (file)
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1255,6 +1255,17 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 
                gelf_getshdr(sec, &shdr);
 
+               /*
+                * If the attribute bit SHF_ALLOC is not set, the section
+                * doesn't occupy memory during process execution.
+                * E.g. ".gnu.warning.*" section is used by linker to generate
+                * warnings when calling deprecated functions, the symbols in
+                * the section aren't loaded to memory during process execution,
+                * so skip them.
+                */
+               if (!(shdr.sh_flags & SHF_ALLOC))
+                       continue;
+
                secstrs = secstrs_sym;
 
                /*