Re: [PATCH v4 0/2] perf: Add is_ignored_kernel_symbol() for kernel symbol filtering

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Fri, May 22, 2026 at 04:26:02PM +0800, Rui Qi wrote:
> The perf tool currently has ad-hoc logic to filter out ELF mapping
> symbols scattered across multiple files. ARM, AArch64 and RISC-V each
> have their own inline checks in dso__load_sym_internal(), and kallsym
> processing has yet another check for ARM module symbols.
> 
> This patch series introduces a single is_ignored_kernel_symbol() inline
> helper in symbol.h and converts the kernel symbol handling paths to use it.
> The helper covers the existing "$" prefix used by ARM, AArch64 and RISC-V,
> and also adds the x86 local symbol prefixes so that perf stays consistent
> with the kernel's own is_mapping_symbol() logic.
> 
> Changes in v4:
>   - Rename the helper from is_mapping_symbol() to is_ignored_kernel_symbol()
>     to make its purpose clearer.
>   - Split the single patch into two logical patches:
>     - Patch 1 introduces the helper and applies it to kallsyms and ksymbol events.
>     - Patch 2 applies the helper to the ELF loading path for kernel DSOs.
> 
> Link (v3): https://lore.kernel.org/all/20260507071103.2772577-1-qirui.001@bytedance.com/
> 
> Changes in v3:
>   - Add is_mapping_symbol() check for kernel modules in dso__load_sym_internal()
>   - Add is_mapping_symbol() check in machine__process_ksymbol_unregister()
> 
> Link (v2): https://lore.kernel.org/all/20260506073820.2419087-1-qirui.001@bytedance.com/
> 
> Changes in v2:
>   - Only apply is_mapping_symbol() filtering to kernel symbols (kallsyms
>     and ksymbol events), not to user-space symbols from ELF files,
>     BFD libraries, or perf map files.  This avoids incorrectly
>     discarding valid user-space function names that start with '$',
>     which is a legal character in identifiers for many languages
>     (e.g., Java, Scala) and compilers (GCC).
>   - Move the mapping symbol check in machine__process_ksymbol_register()
>     to the beginning of the function, before any map/dso allocation
>     or insertion, to avoid leaving empty maps in the kernel map tree.
> 
> Link (v1): https://lore.kernel.org/all/20260504090609.1801880-1-qirui.001@bytedance.com/
> 
> Rui Qi (2):
>   perf: Extract is_ignored_kernel_symbol() for kernel mapping symbol
>     filtering
>   perf: Apply is_ignored_kernel_symbol() filter in ELF loading path for
>     kernel DSOs

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

Thanks,
Namhyung

> 
>  tools/perf/util/machine.c    | 18 +++++++++++++++++-
>  tools/perf/util/symbol-elf.c | 10 ++++++++--
>  tools/perf/util/symbol.c     |  4 ++--
>  tools/perf/util/symbol.h     | 15 +++++++++++++++
>  4 files changed, 42 insertions(+), 5 deletions(-)
> 
> -- 
> 2.20.1