[PATCH v3] perf: Add is_mapping_symbol() helper for kernel mapping symbol filtering

[PATCH v3] perf: Add is_mapping_symbol() helper for kernel mapping symbol filtering

[Rui Qi]

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 is fragile: adding support for a new architecture or adjusting
which prefixes are considered mapping symbols requires touching
multiple places, and it is easy for the checks to diverge. It also
does not match the kernel's own is_mapping_symbol() logic, which
additionally covers x86 local symbols (".L*" and "L0*").

Introduce a single is_mapping_symbol() inline helper in symbol.h and
convert all kernel symbol handling 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.

Signed-off-by: Rui Qi <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/
---
 tools/perf/util/machine.c    | 12 +++++++++++-
 tools/perf/util/symbol-elf.c |  8 ++++++++
 tools/perf/util/symbol.c     |  4 ++--
 tools/perf/util/symbol.h     | 15 +++++++++++++++
 4 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index e76f8c86e62a..4e33ba06111d 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -729,9 +729,15 @@ static int machine__process_ksymbol_register(struct machine *machine,
 {
 	struct symbol *sym;
 	struct dso *dso = NULL;
-	struct map *map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
+	struct map *map;
 	int err = 0;
 
+	/* Ignore mapping symbols in ksymbol events - check early before any state mutation */
+	if (is_mapping_symbol(event->ksymbol.name))
+		return 0;
+
+	map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
+
 	if (!map) {
 		dso = dso__new(event->ksymbol.name);
 
@@ -790,6 +796,10 @@ static int machine__process_ksymbol_unregister(struct machine *machine,
 	struct symbol *sym;
 	struct map *map;
 
+	/* Ignore mapping symbols in ksymbol events */
+	if (is_mapping_symbol(event->ksymbol.name))
+		return 0;
+
 	map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
 	if (!map)
 		return 0;
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 7afa8a117139..6b12508ea58d 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1607,6 +1607,14 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 				continue;
 		}
 
+		/*
+		 * For kernel modules, also reject x86 local symbols (.L* and L0*)
+		 * to match the kernel's is_mapping_symbol() logic and kallsyms
+		 * parsing behavior.
+		 */
+		if (kmodule && is_mapping_symbol(elf_name))
+			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;
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index fcaeeddbbb6b..af03b16c17c6 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -770,8 +770,8 @@ static int map__process_kallsym_symbol(void *arg, const char *name,
 	if (!symbol_type__filter(type))
 		return 0;
 
-	/* Ignore local symbols for ARM modules */
-	if (name[0] == '$')
+	/* Ignore mapping symbols in kallsyms */
+	if (is_mapping_symbol(name))
 		return 0;
 
 	/*
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index bd6eb90c8668..27fa1b43e6f1 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -28,6 +28,21 @@ struct maps;
 struct option;
 struct build_id;
 
+/*
+ * Ignore kernel mapping symbols, matching kernel is_mapping_symbol() logic.
+ * This checks for '$' prefix (used by ARM, AArch64, RISC-V) and
+ * x86 local symbol prefixes (.L* and L0*).
+ * Only use this for kernel symbols (kallsyms, ksymbol events).
+ */
+static inline bool is_mapping_symbol(const char *str)
+{
+	if (str[0] == '.' && str[1] == 'L')
+		return true;
+	if (str[0] == 'L' && str[1] == '0')
+		return true;
+	return str[0] == '$';
+}
+
 /*
  * libelf 0.8.x and earlier do not support ELF_C_READ_MMAP;
  * for newer versions we can use mmap to reduce memory usage:
-- 
2.20.1

Re: [PATCH v3] perf: Add is_mapping_symbol() helper for kernel mapping symbol filtering

[Ian Rogers]

On Thu, May 7, 2026 at 12:11 AM Rui Qi <qirui.001@bytedance.com> 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 is fragile: adding support for a new architecture or adjusting
> which prefixes are considered mapping symbols requires touching
> multiple places, and it is easy for the checks to diverge. It also
> does not match the kernel's own is_mapping_symbol() logic, which
> additionally covers x86 local symbols (".L*" and "L0*").
>
> Introduce a single is_mapping_symbol() inline helper in symbol.h and
> convert all kernel symbol handling to use it. The helper covers the
> existing "$" prefix used by ARM, AArch64 and RISC-V, and also adds
> the x86 local symbol prefixes so that perf stays consistent with
> the kernel.
>
> Signed-off-by: Rui Qi <qirui.001@bytedance.com>
> ---
> Changes in v3:
>   - Add is_mapping_symbol() check for kernel modules in dso__load_sym_internal()
>   - Add is_mapping_symbol() check in machine__process_ksymbol_unregister()
>
> Link (v2): https://lore.kernel.org/all/20260506073820.2419087-1-qirui.001@bytedance.com/
>
> Changes in v2:
>   - Only apply is_mapping_symbol() filtering to kernel symbols (kallsyms
>     and ksymbol events), not to user-space symbols from ELF files,
>     BFD libraries, or perf map files.  This avoids incorrectly
>     discarding valid user-space function names that start with '$',
>     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/
> ---
>  tools/perf/util/machine.c    | 12 +++++++++++-
>  tools/perf/util/symbol-elf.c |  8 ++++++++
>  tools/perf/util/symbol.c     |  4 ++--
>  tools/perf/util/symbol.h     | 15 +++++++++++++++
>  4 files changed, 36 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index e76f8c86e62a..4e33ba06111d 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -729,9 +729,15 @@ static int machine__process_ksymbol_register(struct machine *machine,
>  {
>         struct symbol *sym;
>         struct dso *dso = NULL;
> -       struct map *map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
> +       struct map *map;
>         int err = 0;
>
> +       /* Ignore mapping symbols in ksymbol events - check early before any state mutation */
> +       if (is_mapping_symbol(event->ksymbol.name))
> +               return 0;
> +
> +       map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
> +
>         if (!map) {
>                 dso = dso__new(event->ksymbol.name);
>
> @@ -790,6 +796,10 @@ static int machine__process_ksymbol_unregister(struct machine *machine,
>         struct symbol *sym;
>         struct map *map;
>
> +       /* Ignore mapping symbols in ksymbol events */
> +       if (is_mapping_symbol(event->ksymbol.name))
> +               return 0;
> +
>         map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
>         if (!map)
>                 return 0;
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 7afa8a117139..6b12508ea58d 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1607,6 +1607,14 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
>                                 continue;
>                 }
>
> +               /*
> +                * For kernel modules, also reject x86 local symbols (.L* and L0*)
> +                * to match the kernel's is_mapping_symbol() logic and kallsyms
> +                * parsing behavior.
> +                */
> +               if (kmodule && is_mapping_symbol(elf_name))
> +                       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;
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index fcaeeddbbb6b..af03b16c17c6 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -770,8 +770,8 @@ static int map__process_kallsym_symbol(void *arg, const char *name,
>         if (!symbol_type__filter(type))
>                 return 0;
>
> -       /* Ignore local symbols for ARM modules */
> -       if (name[0] == '$')
> +       /* Ignore mapping symbols in kallsyms */
> +       if (is_mapping_symbol(name))
>                 return 0;
>
>         /*
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index bd6eb90c8668..27fa1b43e6f1 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -28,6 +28,21 @@ struct maps;
>  struct option;
>  struct build_id;
>
> +/*
> + * Ignore kernel mapping symbols, matching kernel is_mapping_symbol() logic.
> + * This checks for '$' prefix (used by ARM, AArch64, RISC-V) and
> + * x86 local symbol prefixes (.L* and L0*).
> + * Only use this for kernel symbols (kallsyms, ksymbol events).
> + */
> +static inline bool is_mapping_symbol(const char *str)

Is there a good reference for what is meant by "mapping symbol" ?
Would "local symbol" be more appropriate for x86? On ARM it seems the
term is well defined:
https://developer.arm.com/documentation/dui0803/a/Accessing-and-managing-symbols-with-armlink/About-mapping-symbols
I'm wondering if we can make this more intention-revealing. I'm
wondering also if we should make the check dependent on the e_machine,
so perhaps:
```
static inline is_ignored_kernel_symbol(const char *name, uint16_t e_machine)
{
  if (e_machine == EM_386 || e_machine == EM_X86_64) {
    /* Local symbols on x86 may start .L or L0. */
   return(str[0] == '.' && str[1] == 'L')  || (str[0] == 'L' && str[1] == '0';
  }
  /* All other machine types. Assume symbols starting $ are mapping
symbols used to denote transitions between different sections of data
and code. */
  return str[0] == '$';
}
```
I think you can use something like `dso__e_machine` at all call sites
to get the ELF machine type for the binary or kernel, but maybe this
is overkill.

Thanks,
Ian

> +{
> +       if (str[0] == '.' && str[1] == 'L')
> +               return true;
> +       if (str[0] == 'L' && str[1] == '0')
> +               return true;
> +       return str[0] == '$';
> +}
> +
>  /*
>   * libelf 0.8.x and earlier do not support ELF_C_READ_MMAP;
>   * for newer versions we can use mmap to reduce memory usage:
> --
> 2.20.1

Re: [PATCH v3] perf: Add is_mapping_symbol() helper for kernel mapping symbol filtering

[Rui Qi]

On 5/7/26 11:23 PM, Ian Rogers wrote:
> On Thu, May 7, 2026 at 12:11 AM Rui Qi <qirui.001@bytedance.com> 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 is fragile: adding support for a new architecture or adjusting
>> which prefixes are considered mapping symbols requires touching
>> multiple places, and it is easy for the checks to diverge. It also
>> does not match the kernel's own is_mapping_symbol() logic, which
>> additionally covers x86 local symbols (".L*" and "L0*").
>>
>> Introduce a single is_mapping_symbol() inline helper in symbol.h and
>> convert all kernel symbol handling to use it. The helper covers the
>> existing "$" prefix used by ARM, AArch64 and RISC-V, and also adds
>> the x86 local symbol prefixes so that perf stays consistent with
>> the kernel.
>>
>> Signed-off-by: Rui Qi <qirui.001@bytedance.com>
>> ---
>> Changes in v3:
>>   - Add is_mapping_symbol() check for kernel modules in dso__load_sym_internal()
>>   - Add is_mapping_symbol() check in machine__process_ksymbol_unregister()
>>
>> Link (v2): https://lore.kernel.org/all/20260506073820.2419087-1-qirui.001@bytedance.com/
>>
>> Changes in v2:
>>   - Only apply is_mapping_symbol() filtering to kernel symbols (kallsyms
>>     and ksymbol events), not to user-space symbols from ELF files,
>>     BFD libraries, or perf map files.  This avoids incorrectly
>>     discarding valid user-space function names that start with '$',
>>     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/
>> ---
>>  tools/perf/util/machine.c    | 12 +++++++++++-
>>  tools/perf/util/symbol-elf.c |  8 ++++++++
>>  tools/perf/util/symbol.c     |  4 ++--
>>  tools/perf/util/symbol.h     | 15 +++++++++++++++
>>  4 files changed, 36 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
>> index e76f8c86e62a..4e33ba06111d 100644
>> --- a/tools/perf/util/machine.c
>> +++ b/tools/perf/util/machine.c
>> @@ -729,9 +729,15 @@ static int machine__process_ksymbol_register(struct machine *machine,
>>  {
>>         struct symbol *sym;
>>         struct dso *dso = NULL;
>> -       struct map *map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
>> +       struct map *map;
>>         int err = 0;
>>
>> +       /* Ignore mapping symbols in ksymbol events - check early before any state mutation */
>> +       if (is_mapping_symbol(event->ksymbol.name))
>> +               return 0;
>> +
>> +       map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
>> +
>>         if (!map) {
>>                 dso = dso__new(event->ksymbol.name);
>>
>> @@ -790,6 +796,10 @@ static int machine__process_ksymbol_unregister(struct machine *machine,
>>         struct symbol *sym;
>>         struct map *map;
>>
>> +       /* Ignore mapping symbols in ksymbol events */
>> +       if (is_mapping_symbol(event->ksymbol.name))
>> +               return 0;
>> +
>>         map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
>>         if (!map)
>>                 return 0;
>> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
>> index 7afa8a117139..6b12508ea58d 100644
>> --- a/tools/perf/util/symbol-elf.c
>> +++ b/tools/perf/util/symbol-elf.c
>> @@ -1607,6 +1607,14 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
>>                                 continue;
>>                 }
>>
>> +               /*
>> +                * For kernel modules, also reject x86 local symbols (.L* and L0*)
>> +                * to match the kernel's is_mapping_symbol() logic and kallsyms
>> +                * parsing behavior.
>> +                */
>> +               if (kmodule && is_mapping_symbol(elf_name))
>> +                       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;
>> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
>> index fcaeeddbbb6b..af03b16c17c6 100644
>> --- a/tools/perf/util/symbol.c
>> +++ b/tools/perf/util/symbol.c
>> @@ -770,8 +770,8 @@ static int map__process_kallsym_symbol(void *arg, const char *name,
>>         if (!symbol_type__filter(type))
>>                 return 0;
>>
>> -       /* Ignore local symbols for ARM modules */
>> -       if (name[0] == '$')
>> +       /* Ignore mapping symbols in kallsyms */
>> +       if (is_mapping_symbol(name))
>>                 return 0;
>>
>>         /*
>> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
>> index bd6eb90c8668..27fa1b43e6f1 100644
>> --- a/tools/perf/util/symbol.h
>> +++ b/tools/perf/util/symbol.h
>> @@ -28,6 +28,21 @@ struct maps;
>>  struct option;
>>  struct build_id;
>>
>> +/*
>> + * Ignore kernel mapping symbols, matching kernel is_mapping_symbol() logic.
>> + * This checks for '$' prefix (used by ARM, AArch64, RISC-V) and
>> + * x86 local symbol prefixes (.L* and L0*).
>> + * Only use this for kernel symbols (kallsyms, ksymbol events).
>> + */
>> +static inline bool is_mapping_symbol(const char *str)
> 
> Is there a good reference for what is meant by "mapping symbol" ?
> Would "local symbol" be more appropriate for x86? On ARM it seems the
> term is well defined:
> https://developer.arm.com/documentation/dui0803/a/Accessing-and-managing-symbols-with-armlink/About-mapping-symbols

Good point. The term "mapping symbol" is indeed well-defined for ARM [1]
and RISC-V [2] — both psabi specifications use "$" prefix symbols to
mark boundaries between code and data regions, and both explicitly call
them "mapping symbols".

However, the ".L*" and "L0*" patterns on x86 are local labels, not
mapping symbols in the same sense. Grouping them under "mapping symbol"
is imprecise.

That said, this naming comes from the existing is_mapping_symbol() in
include/linux/module_symbol.h, which predates this patch. I just
mirrored the kernel-side function into tools/ with an expanded comment.
The terminology question applies to the kernel-side function as well.

I think the comment in my patch should at least not conflate the two.
How about something like:

  /*
   * Ignore symbols that should be skipped in kallsyms output.
   * Matches kernel is_mapping_symbol() logic in module_symbol.h.
   *
   * '$' prefix: ARM/RISC-V mapping symbols ($a, $t, $d, $x, etc.)
   *   See ARM ABI [1] and RISC-V psabi [2].
   * '.L*' and 'L0*': x86 local labels (not mapping symbols per se,
   *   but filtered the same way by the kernel).
   */

A separate cleanup to rename is_mapping_symbol() to something more
accurate (e.g. is_ignorable_symbol()) across the kernel could be done
later, but that's outside the scope of this bugfix.

[1]
https://developer.arm.com/documentation/dui0803/a/Accessing-and-managing-symbols-with-armlink/About-mapping-symbols
[2]
https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#mapping-symbol


> I'm wondering if we can make this more intention-revealing. I'm
> wondering also if we should make the check dependent on the e_machine,
> so perhaps:
> ```
> static inline is_ignored_kernel_symbol(const char *name, uint16_t e_machine)
> {
>   if (e_machine == EM_386 || e_machine == EM_X86_64) {
>     /* Local symbols on x86 may start .L or L0. */
>    return(str[0] == '.' && str[1] == 'L')  || (str[0] == 'L' && str[1] == '0';
>   }
>   /* All other machine types. Assume symbols starting $ are mapping
> symbols used to denote transitions between different sections of data
> and code. */
>   return str[0] == '$';
> }
> ```
> I think you can use something like `dso__e_machine` at all call sites
> to get the ELF machine type for the binary or kernel, but maybe this
> is overkill.
> 
> Thanks,
> Ian
> 

Yes, it's overkill.

The current unconditional checks don't produce false positives across
architectures:

Checking .L / L0 on ARM: ARM assemblers never generate these symbols, so
the check never matches -- it's a no-op.
Checking $ on x86: x86 ELF symbols essentially never start with $, same
story.
The function is functionally correct as-is. Checking for a pattern that
doesn't exist in a given architecture is harmless.

The cost of introducing e_machine is real:

API break: every callsite (kernel/module/kallsyms.c,
scripts/mod/modpost.h) must now pass in architecture info.
e_machine retrieval is non-trivial: the kernel side and modpost side get
ELF headers through different paths, each needing separate adaptation.
Test matrix explosion: one codepath serving all architectures becomes
per-architecture branches, each needing independent verification.
The one thing worth fixing is the function name. is_mapping_symbol
is genuinely misleading -- .L/L0 are local labels, not mapping
symbols. But fixing the name doesn't require an e_machine parameter.
A simple rename to is_ignored_symbol would do.

>> +{
>> +       if (str[0] == '.' && str[1] == 'L')
>> +               return true;
>> +       if (str[0] == 'L' && str[1] == '0')
>> +               return true;
>> +       return str[0] == '$';
>> +}
>> +
>>  /*
>>   * libelf 0.8.x and earlier do not support ELF_C_READ_MMAP;
>>   * for newer versions we can use mmap to reduce memory usage:
>> --
>> 2.20.1

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

[Rui Qi]

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

 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

[PATCH v4 1/2] perf: Extract is_ignored_kernel_symbol() for kernel mapping symbol filtering

[Rui Qi]

Mapping symbol filtering is scattered across multiple files with
inconsistent checks.  The kernel's own is_mapping_symbol() covers
x86 local symbols ('.L*' and 'L0*') on top of the '$' prefix used
by ARM/AArch64/RISC-V, but the perf tool only checks '$'.

Extract is_ignored_kernel_symbol() into symbol.h matching the kernel
definition, and convert the kallsyms and ksymbol event paths to
use it.  Add ksymbol event name validation and early mapping symbol
filtering before any state mutation.

Signed-off-by: Rui Qi <qirui.001@bytedance.com>
---
 tools/perf/util/machine.c | 18 +++++++++++++++++-
 tools/perf/util/symbol.c  |  4 ++--
 tools/perf/util/symbol.h  | 15 +++++++++++++++
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index e76f8c86e62a..07e4ad56d757 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -4,6 +4,7 @@
 #include <inttypes.h>
 #include <regex.h>
 #include <stdlib.h>
+#include <string.h>
 #include "callchain.h"
 #include "debug.h"
 #include "dso.h"
@@ -729,9 +730,15 @@ static int machine__process_ksymbol_register(struct machine *machine,
 {
 	struct symbol *sym;
 	struct dso *dso = NULL;
-	struct map *map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
+	struct map *map;
 	int err = 0;
 
+	/* Ignore mapping symbols in ksymbol events - check early before any state mutation */
+	if (is_ignored_kernel_symbol(event->ksymbol.name))
+		return 0;
+
+	map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
+
 	if (!map) {
 		dso = dso__new(event->ksymbol.name);
 
@@ -790,6 +797,10 @@ static int machine__process_ksymbol_unregister(struct machine *machine,
 	struct symbol *sym;
 	struct map *map;
 
+	/* Ignore mapping symbols in ksymbol events */
+	if (is_ignored_kernel_symbol(event->ksymbol.name))
+		return 0;
+
 	map = maps__find(machine__kernel_maps(machine), event->ksymbol.addr);
 	if (!map)
 		return 0;
@@ -814,6 +825,11 @@ int machine__process_ksymbol(struct machine *machine __maybe_unused,
 	if (dump_trace)
 		perf_event__fprintf_ksymbol(event, stdout);
 
+	if (event->header.size < offsetof(struct perf_record_ksymbol, name) + 2 ||
+	    !memchr(event->ksymbol.name, '\0',
+		    event->header.size - offsetof(struct perf_record_ksymbol, name)))
+		return -EINVAL;
+
 	/* no need to process non-JIT BPF as it cannot get samples */
 	if (event->ksymbol.len == 0)
 		return 0;
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index fcaeeddbbb6b..714b6e6048fa 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -770,8 +770,8 @@ static int map__process_kallsym_symbol(void *arg, const char *name,
 	if (!symbol_type__filter(type))
 		return 0;
 
-	/* Ignore local symbols for ARM modules */
-	if (name[0] == '$')
+	/* Ignore mapping symbols in kallsyms */
+	if (is_ignored_kernel_symbol(name))
 		return 0;
 
 	/*
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index bd6eb90c8668..95592779eb77 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -28,6 +28,21 @@ struct maps;
 struct option;
 struct build_id;
 
+/*
+ * Ignore kernel mapping symbols, matching kernel is_mapping_symbol() logic.
+ * This checks for '$' prefix (used by ARM, AArch64, RISC-V) and
+ * x86 local symbol prefixes (.L* and L0*).
+ * Only use this for kernel symbols (kallsyms, ksymbol events, kernel ELF DSOs).
+ */
+static inline bool is_ignored_kernel_symbol(const char *str)
+{
+	if (str[0] == '.' && str[1] == 'L')
+		return true;
+	if (str[0] == 'L' && str[1] == '0')
+		return true;
+	return str[0] == '$';
+}
+
 /*
  * libelf 0.8.x and earlier do not support ELF_C_READ_MMAP;
  * for newer versions we can use mmap to reduce memory usage:
-- 
2.20.1

[PATCH v4 2/2] perf: Apply is_ignored_kernel_symbol() filter in ELF loading path for kernel DSOs

[Rui Qi]

dso__load_sym_internal() had no filtering for .L* and L0* mapping
symbols while the kallsyms path already filters them via
is_ignored_kernel_symbol().  Add the same check gated by dso__kernel()
so that kernel ELF objects (vmlinux, .ko) have mapping symbols filtered
across all architectures, but userspace ELF objects are unaffected --
'$' is a valid prefix in languages like Java and Scala.

The existing ARM/AArch64 and RISC-V architecture-specific mapping
symbol checks are preserved; the new is_ignored_kernel_symbol() check
adds x86 local symbol (.L*, L0*) filtering and provides unified
cross-architecture coverage for kernel DSOs.

Signed-off-by: Rui Qi <qirui.001@bytedance.com>
---
 tools/perf/util/symbol-elf.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 7afa8a117139..77e6dcba8fda 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1592,9 +1592,11 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 		if (!is_label && !elf_sym__filter(&sym))
 			continue;
 
-		/* Reject ARM ELF "mapping symbols": these aren't unique and
+		/*
+		 * Reject ARM ELF "mapping symbols": these aren't unique and
 		 * don't identify functions, so will confuse the profile
-		 * output: */
+		 * output:
+		 */
 		if (ehdr.e_machine == EM_ARM || ehdr.e_machine == EM_AARCH64) {
 			if (elf_name[0] == '$' && strchr("adtx", elf_name[1])
 			    && (elf_name[2] == '\0' || elf_name[2] == '.'))
@@ -1607,6 +1609,10 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 				continue;
 		}
 
+		/* Reject kernel mapping symbols for kernel DSOs only */
+		if (dso__kernel(dso) && is_ignored_kernel_symbol(elf_name))
+			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;
-- 
2.20.1

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

[Namhyung Kim]

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

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

[Arnaldo Carvalho de Melo]

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