Re: [PATCH v2] perf symbol: remove Rust symbol workarounds

Arnaldo Carvalho de Melo
2026-01-05T15:50:20Z

On Mon, Jan 05, 2026 at 03:00:57PM +0000, Gary Guo wrote:
> From: Gary Guo <gary@garyguo.net>
>
> Due to an off-by-one error introduced in commit 73bbb94466fd ("kallsyms:
> support "big" kernel symbols"), long symbols (which are currently only
> produced by Rust) can have their symbol type being wrongly parsed by
> kernel/kallsyms.c.

Looks sane, applied to perf-tools-next,

- Arnaldo

> This has been fixed in commit f3f9f42232dee5 ("kallsyms: Fix wrong "big"
> kernel symbol type read from procfs"), and these symbols are now
> reported correctly.
>
> Drop the workaround in perf symbol that filter out these symbol types.
>
> Specifically, '1' and 'l' can never be generated by nm -- 'u' does
> indicate GNU unique, however such symbols are only generated by G++ for
> C++ templates, and are never generated by LLVM (LLVM generates weak
> symbols in such cases instead). 'N' can appear if symbols exist inside
> debug sections, and 'n' may appear for symbols inside note sections,
> however these sections do not typically have symbol (and they're
> explicitly filtered out by kallsyms).
>
> Therefore, the previous occurrence of these symbols types must be due to
> the off-by-one error and can be safely removed.
>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Acked-by: Miguel Ojeda <ojeda@kernel.org>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> ---
> v2:
> - Removed the "__" change as suggested by Miguel
> - Expanded the commit message to mention why "N" and "n" cannot appear
> - Link to v1: https://lore.kernel.org/rust-for-linux/20251223175216.1353814-1-gary@kernel.org/#t
> ---
> tools/perf/util/symbol.c | 19 ++++---------------
> 1 file changed, 4 insertions(+), 15 deletions(-)
>
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 814f960fa8f8d..8662001e1e25b 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -104,21 +104,10 @@ static enum dso_binary_type binary_type_symtab[] = {
>
> #define DSO_BINARY_TYPE__SYMTAB_CNT ARRAY_SIZE(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
> - // Ditto for '1':
> - // root@x1:~# grep ' 1 ' /proc/kallsyms
> - // ffffffffb098bc00 1 __pfx__RNCINvNtNtNtCsfwaGRd4cjqE_4core4iter8adapters3map12map_try_foldjNtCskFudTml27HW_12drm_panic_qr7VersionuINtNtNtBa_3ops12control_flow11ControlFlowB10_ENcB10_0NCINvNvNtNtNtB8_6traits8iterator8Iterator4find5checkB10_NCNvMB12_B10_13from_segments0E0E0B12_
> - // ffffffffb098bc10 1 _RNCINvNtNtNtCsfwaGRd4cjqE_4core4iter8adapters3map12map_try_foldjNtCskFudTml27HW_12drm_panic_qr7VersionuINtNtNtBa_3ops12control_flow11ControlFlowB10_ENcB10_0NCINvNvNtNtNtB8_6traits8iterator8Iterator4find5checkB10_NCNvMB12_B10_13from_segments0E0E0B12_
> - 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 == 'N' || __symbol_type == '1';
> +static bool symbol_type__filter(char symbol_type)
> +{
> + symbol_type = toupper(symbol_type);
> + return symbol_type == 'T' || symbol_type == 'W' || symbol_type == 'D' || symbol_type == 'B';
> }
>
> static int prefix_underscores_count(const char *str)
>
> base-commit: 3609fa95fb0f2c1b099e69e56634edb8fc03f87c
> --
> 2.51.2