[PATCH v2] perf symbol: remove Rust symbol workarounds

Gary Guo
2026-01-05T15:01:16Z

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.

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