[PATCH next 1/1] perf symbols: Handle 'N' symbols in /proc/kallsyms

[Arnaldo Carvalho de Melo <acme@kernel.org>]

I started seeing this in recent Fedora 42 kernels:

  # uname -a
  Linux number 6.16.3-200.fc42.x86_64 #1 SMP PREEMPT_DYNAMIC Sat Aug 23 17:02:17 UTC 2025 x86_64 GNU/Linux
  #
  # perf test vmlinux
    1: vmlinux symtab matches kallsyms                  : FAILED!
  #

Rust is enabled and these were the symbols causing the above failure,
i.e. found in vmlinux but not in /proc/kallsyms:

  $ grep -w N /proc/kallsyms
  0000000000000000 N __pfx__RNCINvNtNtNtCsbDUBuN8AbD4_4core4iter8adapters3map12map_try_foldjNtCs6vVzKs5jPr6_12drm_panic_qr7VersionuINtNtNtBa_3ops12control_flow11ControlFlowB10_ENcB10_0NCINvNvNtNtNtB8_6traits8iterator8Iterator4find5checkB10_NCNvMB12_B10_13from_segments0E0E0B12_
  0000000000000000 N _RNCINvNtNtNtCsbDUBuN8AbD4_4core4iter8adapters3map12map_try_foldjNtCs6vVzKs5jPr6_12drm_panic_qr7VersionuINtNtNtBa_3ops12control_flow11ControlFlowB10_ENcB10_0NCINvNvNtNtNtB8_6traits8iterator8Iterator4find5checkB10_NCNvMB12_B10_13from_segments0E0E0B12_
  $

So accept those 'N' symbols as well.

About them, from 'man nm':

           "N" The symbol is a debugging symbol.

           "n" The symbol is in a non-data, non-code, non-debug read-only section.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/symbol.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 3fed54de54016227..3d04382687d17d22 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -107,9 +107,14 @@ static enum dso_binary_type binary_type_symtab[] = {
 static bool symbol_type__filter(char __symbol_type)
 {
 	// Since 'U' == undefined and 'u' == unique global symbol, we can't use toupper there
+	// 'N' is for debugging symbols, 'n' is a non-data, non-code, non-debug read-only section.
+	// According to 'man nm'.
+	// 'N' first seen in:
+	// ffffffff9b35d130 N __pfx__RNCINvNtNtNtCsbDUBuN8AbD4_4core4iter8adapters3map12map_try_foldjNtCs6vVzKs5jPr6_12drm_panic_qr7VersionuINtNtNtBa_3ops12control_flow11ControlFlowB10_ENcB10_0NCINvNvNtNtNtB8_6traits8iterator8Iterator4find5checkB10_NCNvMB12_B10_13from_segments0E0E0B12_
+	// a seemingly Rust mangled name
 	char symbol_type = toupper(__symbol_type);
 	return symbol_type == 'T' || symbol_type == 'W' || symbol_type == 'D' || symbol_type == 'B' ||
-	       __symbol_type == 'u' || __symbol_type == 'l';
+	       __symbol_type == 'u' || __symbol_type == 'l' || __symbol_type == 'N';
 }
 
 static int prefix_underscores_count(const char *str)
-- 
2.51.0