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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Mon, May 25, 2026 at 09:04:11PM -0500, Namhyung Kim wrote:
> 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, applied to perf-tools-next, for v7.2.

- Arnaldo