[PATCH v4 0/3] Ignore local labels and mapping symbols during module load

[PATCH v4 0/3] Ignore local labels and mapping symbols during module load

[Tiezhu Yang]

This series prevents compiler generated local labels and mapping symbols
from leaking into /proc/kallsyms for loaded modules. This ensures tracing
tools like bpftrace can resolve accurate kernel stacks on architectures
like LoongArch.

Based on the latest modules-next tree:
https://git.kernel.org/pub/scm/linux/kernel/git/modules/linux.git/log/?h=modules-next

There are many discussions in the previous version, here is the link:
https://lore.kernel.org/loongarch/20260812032807.15034-1-yangtiezhu@loongson.cn/

v4:
  (1) Use is_ignored_kernel_symbol() and update
      tools/perf/util/symbol.h in patch #1
  (2) Keep using is_core_symbol() in patch #2
  (3) Update commit messages of the three patches

Cc the maintainers of the updated non-module files:
  (1) Josh Poimboeuf <jpoimboe@kernel.org> -- scripts/faddr2line
  (2) Nathan Chancellor <nathan@kernel.org> -- scripts/mod/modpost.h
  (3) Namhyung Kim <namhyung@kernel.org> -- tools/perf/util/symbol.h

Tiezhu Yang (3):
  module/kallsyms: Rename is_mapping_symbol() to
    is_ignored_kernel_symbol()
  module/kallsyms: Refactor current symbol filtering into
    is_core_symbol()
  module/kallsyms: Ignore local labels and mapping symbols during module
    load

 include/linux/module_symbol.h |  7 +++--
 kernel/module/kallsyms.c      | 59 ++++++++++++++++++-----------------
 scripts/faddr2line            |  2 +-
 scripts/mod/modpost.h         |  2 +-
 tools/perf/util/symbol.h      |  4 +--
 5 files changed, 39 insertions(+), 35 deletions(-)

-- 
2.42.0

[PATCH v4 1/3] module/kallsyms: Rename is_mapping_symbol() to is_ignored_kernel_symbol()

[Tiezhu Yang]

The helper function is_mapping_symbol() historically checks for both
local labels prefixed with ".L" or "L0" and mapping symbols prefixed
with "$".

Rename it to is_ignored_kernel_symbol() to better reflect this actual
behavior and scope, preventing conceptual confusion.

While at it, update the related non-module files, no functional changes.

Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
---
 include/linux/module_symbol.h | 7 +++++--
 kernel/module/kallsyms.c      | 2 +-
 scripts/faddr2line            | 2 +-
 scripts/mod/modpost.h         | 2 +-
 tools/perf/util/symbol.h      | 4 +---
 5 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/linux/module_symbol.h b/include/linux/module_symbol.h
index 574609aced99..698d3db2b37e 100644
--- a/include/linux/module_symbol.h
+++ b/include/linux/module_symbol.h
@@ -7,8 +7,11 @@ enum ksym_flags {
 	KSYM_FLAG_GPL_ONLY	= 1 << 0,
 };
 
-/* This ignores the intensely annoying "mapping symbols" found in ELF files. */
-static inline bool is_mapping_symbol(const char *str)
+/*
+ * Ignore local labels (.L*, L0*) and mapping symbols ($*). These symbols are
+ * not useful for the kernel, for example, they should not appear in kallsyms.
+ */
+static inline bool is_ignored_kernel_symbol(const char *str)
 {
 	if (str[0] == '.' && str[1] == 'L')
 		return true;
diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index f23126d804b2..a52942fd0e07 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -294,7 +294,7 @@ static const char *find_kallsyms_symbol(struct module *mod,
 		 * and inserted at a whim.
 		 */
 		if (*kallsyms_symbol_name(kallsyms, i) == '\0' ||
-		    is_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
+		    is_ignored_kernel_symbol(kallsyms_symbol_name(kallsyms, i)))
 			continue;
 
 		if (thisval <= addr && thisval > bestval) {
diff --git a/scripts/faddr2line b/scripts/faddr2line
index 622875396bcf..3aca197d513f 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -243,7 +243,7 @@ __faddr2line() {
 			local cur_sym_elf_size=${fields[2]}
 			local cur_sym_name=${fields[7]:-}
 
-			# is_mapping_symbol(cur_sym_name)
+			# is_ignored_kernel_symbol(cur_sym_name)
 			if [[ ${cur_sym_name} =~ ^(\.L|L0|\$) ]]; then
 				continue
 			fi
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 2aecb8f25c87..d9c21d479dd8 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -198,7 +198,7 @@ static inline bool is_valid_name(struct elf_info *elf, Elf_Sym *sym)
 
 	if (!name || !strlen(name))
 		return false;
-	return !is_mapping_symbol(name);
+	return !is_ignored_kernel_symbol(name);
 }
 
 /* symsearch.c */
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index a71525335703..8b0780046938 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -31,9 +31,7 @@ struct build_id;
 struct perf_env;
 
 /*
- * 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*).
+ * Ignore local labels and mapping symbols, matching kernel is_ignored_kernel_symbol() logic.
  * Only use this for kernel symbols (kallsyms, ksymbol events, kernel ELF DSOs).
  */
 static inline bool is_ignored_kernel_symbol(const char *str)
-- 
2.42.0

Re: [PATCH v4 1/3] module/kallsyms: Rename is_mapping_symbol() to is_ignored_kernel_symbol()

[Huacai Chen]

Hi, Tiezhu,

On Thu, Aug 20, 2026 at 8:50 PM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> The helper function is_mapping_symbol() historically checks for both
> local labels prefixed with ".L" or "L0" and mapping symbols prefixed
> with "$".
>
> Rename it to is_ignored_kernel_symbol() to better reflect this actual
> behavior and scope, preventing conceptual confusion.
I think is_ignored_symbol() is enough, no "kernel" needed.

Huacai

>
> While at it, update the related non-module files, no functional changes.
>
> Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
> ---
>  include/linux/module_symbol.h | 7 +++++--
>  kernel/module/kallsyms.c      | 2 +-
>  scripts/faddr2line            | 2 +-
>  scripts/mod/modpost.h         | 2 +-
>  tools/perf/util/symbol.h      | 4 +---
>  5 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/module_symbol.h b/include/linux/module_symbol.h
> index 574609aced99..698d3db2b37e 100644
> --- a/include/linux/module_symbol.h
> +++ b/include/linux/module_symbol.h
> @@ -7,8 +7,11 @@ enum ksym_flags {
>         KSYM_FLAG_GPL_ONLY      = 1 << 0,
>  };
>
> -/* This ignores the intensely annoying "mapping symbols" found in ELF files. */
> -static inline bool is_mapping_symbol(const char *str)
> +/*
> + * Ignore local labels (.L*, L0*) and mapping symbols ($*). These symbols are
> + * not useful for the kernel, for example, they should not appear in kallsyms.
> + */
> +static inline bool is_ignored_kernel_symbol(const char *str)
>  {
>         if (str[0] == '.' && str[1] == 'L')
>                 return true;
> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
> index f23126d804b2..a52942fd0e07 100644
> --- a/kernel/module/kallsyms.c
> +++ b/kernel/module/kallsyms.c
> @@ -294,7 +294,7 @@ static const char *find_kallsyms_symbol(struct module *mod,
>                  * and inserted at a whim.
>                  */
>                 if (*kallsyms_symbol_name(kallsyms, i) == '\0' ||
> -                   is_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
> +                   is_ignored_kernel_symbol(kallsyms_symbol_name(kallsyms, i)))
>                         continue;
>
>                 if (thisval <= addr && thisval > bestval) {
> diff --git a/scripts/faddr2line b/scripts/faddr2line
> index 622875396bcf..3aca197d513f 100755
> --- a/scripts/faddr2line
> +++ b/scripts/faddr2line
> @@ -243,7 +243,7 @@ __faddr2line() {
>                         local cur_sym_elf_size=${fields[2]}
>                         local cur_sym_name=${fields[7]:-}
>
> -                       # is_mapping_symbol(cur_sym_name)
> +                       # is_ignored_kernel_symbol(cur_sym_name)
>                         if [[ ${cur_sym_name} =~ ^(\.L|L0|\$) ]]; then
>                                 continue
>                         fi
> diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
> index 2aecb8f25c87..d9c21d479dd8 100644
> --- a/scripts/mod/modpost.h
> +++ b/scripts/mod/modpost.h
> @@ -198,7 +198,7 @@ static inline bool is_valid_name(struct elf_info *elf, Elf_Sym *sym)
>
>         if (!name || !strlen(name))
>                 return false;
> -       return !is_mapping_symbol(name);
> +       return !is_ignored_kernel_symbol(name);
>  }
>
>  /* symsearch.c */
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index a71525335703..8b0780046938 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -31,9 +31,7 @@ struct build_id;
>  struct perf_env;
>
>  /*
> - * Ignore kernel mapping symbols, matching kernel is_mapping_symbol() logic.
> - * This checks for '$' prefix (used by ARM, AArch64, RISC-V) and
> - * x86 local symbol prefixes (.L* and L0*).
> + * Ignore local labels and mapping symbols, matching kernel is_ignored_kernel_symbol() logic.
>   * Only use this for kernel symbols (kallsyms, ksymbol events, kernel ELF DSOs).
>   */
>  static inline bool is_ignored_kernel_symbol(const char *str)
> --
> 2.42.0
>
>

Re: [PATCH v4 1/3] module/kallsyms: Rename is_mapping_symbol() to is_ignored_kernel_symbol()

[Tiezhu Yang]

On 2026/8/24 下午4:45, Huacai Chen wrote:
> Hi, Tiezhu,
> 
> On Thu, Aug 20, 2026 at 8:50 PM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>>
>> The helper function is_mapping_symbol() historically checks for both
>> local labels prefixed with ".L" or "L0" and mapping symbols prefixed
>> with "$".
>>
>> Rename it to is_ignored_kernel_symbol() to better reflect this actual
>> behavior and scope, preventing conceptual confusion.
> I think is_ignored_symbol() is enough, no "kernel" needed.

Hi Huacai,

Using is_ignored_kernel_symbol() was suggested by Petr [1] to maintain
consistency with the existing naming convention in tools/perf.

For me, either is_ignored_kernel_symbol() or is_ignored_symbol() is
fine. I will leave it to Petr to make the final call on this.

[1] 
https://lore.kernel.org/loongarch/96b0e23b-165d-4026-bdfe-f8cd8ceb36ba@suse.com/

Thanks,
Tiezhu

Re: [PATCH v4 1/3] module/kallsyms: Rename is_mapping_symbol() to is_ignored_kernel_symbol()

[Petr Pavlu]

On 8/20/26 2:50 PM, Tiezhu Yang wrote:
> The helper function is_mapping_symbol() historically checks for both
> local labels prefixed with ".L" or "L0" and mapping symbols prefixed
> with "$".
> 
> Rename it to is_ignored_kernel_symbol() to better reflect this actual
> behavior and scope, preventing conceptual confusion.
> 
> While at it, update the related non-module files, no functional changes.
> 
> Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>

Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>

-- 
Thanks,
Petr

[PATCH v4 2/3] module/kallsyms: Refactor current symbol filtering into is_core_symbol()

[Tiezhu Yang]

Currently, the loops in layout_symtab() and add_kallsyms() duplicate the
exact same checks (i == 0 || is_livepatch_module() || is_core_symbol())
to determine whether a symbol should be preserved in the module's core
symbol table.

Move the entire checking logic inside is_core_symbol(), including the
special handlers for the first symbol and livepatch modules.

No functional changes.

Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
---
 kernel/module/kallsyms.c | 54 ++++++++++++++++++++--------------------
 1 file changed, 27 insertions(+), 27 deletions(-)

diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index a52942fd0e07..d75c9f60d360 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -75,23 +75,26 @@ static char elf_type(const Elf_Sym *sym, const struct load_info *info)
 	return '?';
 }
 
-static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,
-			   unsigned int shnum, unsigned int pcpundx)
+static bool is_core_symbol(struct module *mod, const struct load_info *info,
+			   unsigned int symnum, const Elf_Sym *src)
 {
 	const Elf_Shdr *sec;
 	enum mod_mem_type type;
 
+	if (symnum == 0 || is_livepatch_module(mod))
+		return true;
+
 	if (src->st_shndx == SHN_UNDEF ||
-	    src->st_shndx >= shnum ||
+	    src->st_shndx >= info->hdr->e_shnum ||
 	    !src->st_name)
 		return false;
 
 #ifdef CONFIG_KALLSYMS_ALL
-	if (src->st_shndx == pcpundx)
+	if (src->st_shndx == info->index.pcpu)
 		return true;
 #endif
 
-	sec = sechdrs + src->st_shndx;
+	sec = info->sechdrs + src->st_shndx;
 	type = sec->sh_entsize >> SH_ENTSIZE_TYPE_SHIFT;
 	if (!(sec->sh_flags & SHF_ALLOC)
 #ifndef CONFIG_KALLSYMS_ALL
@@ -130,12 +133,11 @@ void layout_symtab(struct module *mod, struct load_info *info)
 
 	/* Compute total space required for the core symbols' strtab. */
 	for (ndst = i = 0; i < nsrc; i++) {
-		if (i == 0 || is_livepatch_module(mod) ||
-		    is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
-				   info->index.pcpu)) {
-			strtab_size += strlen(&info->strtab[src[i].st_name]) + 1;
-			ndst++;
-		}
+		if (!is_core_symbol(mod, info, i, src + i))
+			continue;
+
+		strtab_size += strlen(&info->strtab[src[i].st_name]) + 1;
+		ndst++;
 	}
 
 	/* Append room for core symbols at end of core part. */
@@ -197,23 +199,21 @@ void add_kallsyms(struct module *mod, const struct load_info *info)
 	strtab_size = info->core_typeoffs - info->stroffs;
 	src = kallsyms->symtab;
 	for (ndst = i = 0; i < kallsyms->num_symtab; i++) {
+		ssize_t ret;
+
 		kallsyms->typetab[i] = elf_type(src + i, info);
-		if (i == 0 || is_livepatch_module(mod) ||
-		    is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
-				   info->index.pcpu)) {
-			ssize_t ret;
-
-			mod->core_kallsyms.typetab[ndst] =
-				kallsyms->typetab[i];
-			dst[ndst] = src[i];
-			dst[ndst++].st_name = s - mod->core_kallsyms.strtab;
-			ret = strscpy(s, &kallsyms->strtab[src[i].st_name],
-				      strtab_size);
-			if (ret < 0)
-				break;
-			s += ret + 1;
-			strtab_size -= ret + 1;
-		}
+
+		if (!is_core_symbol(mod, info, i, src + i))
+			continue;
+
+		mod->core_kallsyms.typetab[ndst] = kallsyms->typetab[i];
+		dst[ndst] = src[i];
+		dst[ndst++].st_name = s - mod->core_kallsyms.strtab;
+		ret = strscpy(s, &kallsyms->strtab[src[i].st_name], strtab_size);
+		if (ret < 0)
+			break;
+		s += ret + 1;
+		strtab_size -= ret + 1;
 	}
 
 	/* Set up to point into init section. */
-- 
2.42.0

[PATCH v4 3/3] module/kallsyms: Ignore local labels and mapping symbols during module load

[Tiezhu Yang]

The compiler toolchains may generate local labels and mapping symbols on
certain architectures like LoongArch for optimizations and relocations.

While these local labels and mapping symbols are already ignored during
runtime lookups via find_kallsyms_symbol(), they still leak into kallsyms
for loaded modules because layout_symtab() and add_kallsyms() don't ignore
them during load time.

Consequently, tracing tools like bpftrace (which do not perform internal
filtering, unlike perf) resolve identical addresses into confusing local
labels instead of actual clear C function names.

Fix this by integrating the is_ignored_kernel_symbol() check directly into
is_core_symbol(). This ensures these unneeded symbols are stripped during
module load time, keeping /proc/kallsyms clean and resulting in accurate
call stacks.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
---
 kernel/module/kallsyms.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index d75c9f60d360..1ff8ce857d92 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -89,6 +89,9 @@ static bool is_core_symbol(struct module *mod, const struct load_info *info,
 	    !src->st_name)
 		return false;
 
+	if (is_ignored_kernel_symbol(&info->strtab[src->st_name]))
+		return false;
+
 #ifdef CONFIG_KALLSYMS_ALL
 	if (src->st_shndx == info->index.pcpu)
 		return true;
-- 
2.42.0