Documentation/process/changes.rst | 4 ++-- lib/Kconfig.debug | 10 ++++++++++ scripts/Makefile.btf | 6 +++++- 3 files changed, 17 insertions(+), 3 deletions(-)
decl_tag_kfuncs was implemented in pahole v1.27 (dwarves commit
72e88f29c6f7 [1]). However, ebb79e96f1ea ("kbuild: bpf: Tell pahole
to DECL_TAG kfuncs") appended it to the list of --btf_features flags
already gated on pahole >= 1.26, making it silently inactive on any
pahole v1.26 build.
Without decl_tag_kfuncs, pahole does not emit DECL_TAG BTF entries for
__bpf_kfunc-annotated functions. resolve_btfids then skips
process_kfunc_with_implicit_args(), so KF_IMPLICIT_ARGS kfuncs keep
their full prototype (including the implicit aux parameter) in vmlinux
BTF. BPF programs loading such kfuncs as weak ksyms fail with:
libbpf: extern (func ksym) 'scx_bpf_create_dsq': func_proto [N]
incompatible with vmlinux [M]
Fix by splitting decl_tag_kfuncs into its own >= 127 line in
Makefile.btf. Add a PAHOLE_HAS_DECL_TAG_KFUNCS Kconfig symbol so
build rules can gate on this feature explicitly. Update
Documentation/process/changes.rst to reflect the corrected minimum
pahole version for KF_IMPLICIT_ARGS support.
[1] https://github.com/acmel/dwarves/commit/72e88f29c6f7e14201756e65bd66157427a61aaf
Fixes: ebb79e96f1ea ("kbuild: bpf: Tell pahole to DECL_TAG kfuncs")
Reported-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Closes: https://lore.kernel.org/bpf/e0ca748d-3204-4160-b37d-0f76cbac8c6c@linux.dev/
Signed-off-by: zhidao su <suzhidao@xiaomi.com>
---
Documentation/process/changes.rst | 4 ++--
lib/Kconfig.debug | 10 ++++++++++
scripts/Makefile.btf | 6 +++++-
3 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
index 02068d72a101..bfe98e38c9c0 100644
--- a/Documentation/process/changes.rst
+++ b/Documentation/process/changes.rst
@@ -38,7 +38,7 @@ bash 4.2 bash --version
binutils 2.30 ld -v
flex 2.5.35 flex --version
bison 2.0 bison --version
-pahole 1.26 pahole --version
+pahole 1.27 pahole --version
util-linux 2.10o mount --version
kmod 13 depmod -V
e2fsprogs 1.41.4 e2fsck -V
@@ -145,7 +145,7 @@ Since Linux 5.2, if CONFIG_DEBUG_INFO_BTF is selected, the build system
generates BTF (BPF Type Format) from DWARF in vmlinux, a bit later from kernel
modules as well. This requires pahole v1.22 or later.
-Since Linux 7.0, kfuncs annotated with KF_IMPLICIT_ARGS require pahole v1.26
+Since Linux 7.0, kfuncs annotated with KF_IMPLICIT_ARGS require pahole v1.27
or later. Without it, such kfuncs will have incorrect BTF prototypes in
vmlinux, causing BPF programs to fail to load with a "func_proto incompatible
with vmlinux" error. Many sched_ext kfuncs are affected.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 93f356d2b3d9..38ef8b6ce98d 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -425,6 +425,16 @@ config PAHOLE_HAS_LANG_EXCLUDE
otherwise it would emit malformed kernel and module binaries when
using DEBUG_INFO_BTF_MODULES.
+config PAHOLE_HAS_DECL_TAG_KFUNCS
+ def_bool PAHOLE_VERSION >= 127
+ help
+ Support for the decl_tag_kfuncs BTF feature, which is required for
+ kfuncs annotated with KF_IMPLICIT_ARGS to receive correct BTF
+ prototypes. Without it, such kfuncs retain their full prototype
+ (including the implicit aux parameter) in vmlinux BTF, causing BPF
+ programs to fail to load with a "func_proto incompatible" error.
+ Implemented in pahole v1.27 (commit 72e88f29c).
+
config DEBUG_INFO_BTF_MODULES
bool "Generate BTF type information for kernel modules"
default y
diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
index 562a04b40e06..c804643c5040 100644
--- a/scripts/Makefile.btf
+++ b/scripts/Makefile.btf
@@ -14,7 +14,11 @@ pahole-flags-$(call test-ge, $(pahole-ver), 125) += --skip_encoding_btf_inconsis
else
# Switch to using --btf_features for v1.26 and later.
-pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j$(JOBS) --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
+pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j$(JOBS) --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func
+
+# decl_tag_kfuncs was implemented in pahole v1.27 (commit 72e88f29c).
+# It was incorrectly gated on >= 126 by ebb79e96f1ea.
+pahole-flags-$(call test-ge, $(pahole-ver), 127) += --btf_features=decl_tag_kfuncs
pahole-flags-$(call test-ge, $(pahole-ver), 130) += --btf_features=attributes
--
2.43.0On 3/26/26 5:24 PM, zhidao su wrote:
> decl_tag_kfuncs was implemented in pahole v1.27 (dwarves commit
> 72e88f29c6f7 [1]). However, ebb79e96f1ea ("kbuild: bpf: Tell pahole
> to DECL_TAG kfuncs") appended it to the list of --btf_features flags
> already gated on pahole >= 1.26, making it silently inactive on any
> pahole v1.26 build.
>
> Without decl_tag_kfuncs, pahole does not emit DECL_TAG BTF entries for
> __bpf_kfunc-annotated functions. resolve_btfids then skips
> process_kfunc_with_implicit_args(), so KF_IMPLICIT_ARGS kfuncs keep
> their full prototype (including the implicit aux parameter) in vmlinux
> BTF. BPF programs loading such kfuncs as weak ksyms fail with:
>
> libbpf: extern (func ksym) 'scx_bpf_create_dsq': func_proto [N]
> incompatible with vmlinux [M]
>
> Fix by splitting decl_tag_kfuncs into its own >= 127 line in
> Makefile.btf. Add a PAHOLE_HAS_DECL_TAG_KFUNCS Kconfig symbol so
> build rules can gate on this feature explicitly. Update
> Documentation/process/changes.rst to reflect the corrected minimum
> pahole version for KF_IMPLICIT_ARGS support.
>
> [1] https://github.com/acmel/dwarves/commit/72e88f29c6f7e14201756e65bd66157427a61aaf
>
> Fixes: ebb79e96f1ea ("kbuild: bpf: Tell pahole to DECL_TAG kfuncs")
> Reported-by: Ihor Solodrai <ihor.solodrai@linux.dev>
> Closes: https://lore.kernel.org/bpf/e0ca748d-3204-4160-b37d-0f76cbac8c6c@linux.dev/
No. Please read the feedback behind this link carefully and check the
patch bumping to v1.22 before submitting a new version.
Hint: you can feed it to your "AI agent" too, it should be able to
figure it out.
We don't need a new kconfig flag to enforce higher minimum pahole version.
pw-bot: cr
> Signed-off-by: zhidao su <suzhidao@xiaomi.com>
> ---
> Documentation/process/changes.rst | 4 ++--
> lib/Kconfig.debug | 10 ++++++++++
> scripts/Makefile.btf | 6 +++++-
> 3 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
> index 02068d72a101..bfe98e38c9c0 100644
> --- a/Documentation/process/changes.rst
> +++ b/Documentation/process/changes.rst
> @@ -38,7 +38,7 @@ bash 4.2 bash --version
> binutils 2.30 ld -v
> flex 2.5.35 flex --version
> bison 2.0 bison --version
> -pahole 1.26 pahole --version
> +pahole 1.27 pahole --version
> util-linux 2.10o mount --version
> kmod 13 depmod -V
> e2fsprogs 1.41.4 e2fsck -V
> @@ -145,7 +145,7 @@ Since Linux 5.2, if CONFIG_DEBUG_INFO_BTF is selected, the build system
> generates BTF (BPF Type Format) from DWARF in vmlinux, a bit later from kernel
> modules as well. This requires pahole v1.22 or later.
>
> -Since Linux 7.0, kfuncs annotated with KF_IMPLICIT_ARGS require pahole v1.26
> +Since Linux 7.0, kfuncs annotated with KF_IMPLICIT_ARGS require pahole v1.27
> or later. Without it, such kfuncs will have incorrect BTF prototypes in
> vmlinux, causing BPF programs to fail to load with a "func_proto incompatible
> with vmlinux" error. Many sched_ext kfuncs are affected.
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 93f356d2b3d9..38ef8b6ce98d 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -425,6 +425,16 @@ config PAHOLE_HAS_LANG_EXCLUDE
> otherwise it would emit malformed kernel and module binaries when
> using DEBUG_INFO_BTF_MODULES.
>
> +config PAHOLE_HAS_DECL_TAG_KFUNCS
> + def_bool PAHOLE_VERSION >= 127
> + help
> + Support for the decl_tag_kfuncs BTF feature, which is required for
> + kfuncs annotated with KF_IMPLICIT_ARGS to receive correct BTF
> + prototypes. Without it, such kfuncs retain their full prototype
> + (including the implicit aux parameter) in vmlinux BTF, causing BPF
> + programs to fail to load with a "func_proto incompatible" error.
> + Implemented in pahole v1.27 (commit 72e88f29c).
> +
> config DEBUG_INFO_BTF_MODULES
> bool "Generate BTF type information for kernel modules"
> default y
> diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
> index 562a04b40e06..c804643c5040 100644
> --- a/scripts/Makefile.btf
> +++ b/scripts/Makefile.btf
> @@ -14,7 +14,11 @@ pahole-flags-$(call test-ge, $(pahole-ver), 125) += --skip_encoding_btf_inconsis
> else
>
> # Switch to using --btf_features for v1.26 and later.
> -pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j$(JOBS) --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
> +pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j$(JOBS) --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func
> +
> +# decl_tag_kfuncs was implemented in pahole v1.27 (commit 72e88f29c).
> +# It was incorrectly gated on >= 126 by ebb79e96f1ea.
> +pahole-flags-$(call test-ge, $(pahole-ver), 127) += --btf_features=decl_tag_kfuncs
>
> pahole-flags-$(call test-ge, $(pahole-ver), 130) += --btf_features=attributes
>
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