linux-kernel - Re: [PATCH] perf symbols: Ignore mapping symbols on riscv

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Message-ID: <Z_hoH0fu_NnEUUfe@google.com>
Date: Thu, 10 Apr 2025 17:53:51 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Haibo Xu <haibo1.xu@...el.com>
Cc: xiaobo55x@...il.com, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	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>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>,
	Stephen Brennan <stephen.s.brennan@...cle.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] perf symbols: Ignore mapping symbols on riscv

Hello,

On Wed, Apr 09, 2025 at 10:51:56AM +0800, Haibo Xu wrote:
> RISCV ELF use mapping symbols with special names $x, $d to
> identify regions of RISCV code or code with different ISAs[1].
> These symbols don't identify functions, so will confuse the
> perf output.
> 
> The patch filters out these symbols at load time, similar to
> "4886f2ca perf symbols: Ignore mapping symbols on aarch64".
> 
> [1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/
>     master/riscv-elf.adoc#mapping-symbol
> 
> Signed-off-by: Haibo Xu <haibo1.xu@...el.com>

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung


> ---
>  tools/perf/util/symbol-elf.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index fbf6d0f73af9..55b1409b0593 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1733,6 +1733,12 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
>  				continue;
>  		}
>  
> +		/* Reject RISCV ELF "mapping symbols" */
> +		if (ehdr.e_machine == EM_RISCV) {
> +			if (elf_name[0] == '$' && strchr("dx", elf_name[1]))
> +				continue;
> +		}
> +
>  		if (runtime_ss->opdsec && sym.st_shndx == runtime_ss->opdidx) {
>  			u32 offset = sym.st_value - syms_ss->opdshdr.sh_addr;
>  			u64 *opd = opddata->d_buf + offset;
> -- 
> 2.43.0
>