linux-kernel - Re: [PATCH next 1/1] perf symbols: Handle 'N' symbols in /proc/kallsyms

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Message-ID: <CAP-5=fUYfZyvOpH2rTzMfoz0_uqmHRucwP=tgNB6=pigrowR1g@mail.gmail.com>
Date: Mon, 8 Sep 2025 14:50:55 -0700
From: Ian Rogers <irogers@...gle.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	Miguel Ojeda <ojeda@...nel.org>, James Clark <james.clark@...aro.org>, Jiri Olsa <jolsa@...nel.org>, 
	Kan Liang <kan.liang@...ux.intel.com>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH next 1/1] perf symbols: Handle 'N' symbols in /proc/kallsyms

On Mon, Sep 8, 2025 at 1:54 PM Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>
> 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@...el.com>
> Cc: Ian Rogers <irogers@...gle.com>
> Cc: Miguel Ojeda <ojeda@...nel.org>
> Cc: James Clark <james.clark@...aro.org>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>

Reviewed-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  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
>