linux-kernel - Re: [PATCH v2] perf symbol: remove Rust symbol workarounds

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Message-ID: <aV4TkNE_hAyByISq@google.com>
Date: Wed, 7 Jan 2026 00:04:32 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Gary Guo <gary@...yguo.net>, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	James Clark <james.clark@...aro.org>,
	Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>,
	Stephen Brennan <stephen.s.brennan@...cle.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v2] perf symbol: remove Rust symbol workarounds

Hello,

On Mon, Jan 05, 2026 at 12:50:15PM -0300, Arnaldo Carvalho de Melo wrote:
> On Mon, Jan 05, 2026 at 03:00:57PM +0000, Gary Guo wrote:
> > From: Gary Guo <gary@...yguo.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,
  
I'm afraid there may be some outdated kernels which don't have the fix
yet.  Maybe make sense to wait some more time for them to disappear?

Thanks,
Namhyung


> > 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@...hat.com>
> > Acked-by: Miguel Ojeda <ojeda@...nel.org>
> > Signed-off-by: Gary Guo <gary@...yguo.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