[PATCH bpf-next v3] bpftool: Add support for custom BTF path in prog load/loadall

[PATCH bpf-next v3] bpftool: Add support for custom BTF path in prog load/loadall

[Jiayuan Chen]

This patch exposes the btf_custom_path feature to bpftool, allowing users
to specify a custom BTF file when loading BPF programs using prog load or
prog loadall commands.

The argument 'btf_custom_path' in libbpf is used for those kernels that
don't have CONFIG_DEBUG_INFO_BTF enabled but still want to perform CO-RE
relocations.

Suggested-by: Quentin Monnet <qmo@kernel.org>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>

---
V2 -> V3: Optimized document grammar and some prompts
https://lore.kernel.org/bpf/20250515065018.240188-1-jiayuan.chen@linux.dev/
V1 -> V2: Added bash completion and documentation
https://lore.kernel.org/bpf/20250513035853.75820-1-jiayuan.chen@linux.dev/
---
 tools/bpf/bpftool/Documentation/bpftool-prog.rst |  8 +++++++-
 tools/bpf/bpftool/bash-completion/bpftool        |  4 ++--
 tools/bpf/bpftool/prog.c                         | 12 +++++++++++-
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
index d6304e01afe0..4dce43e8e8a3 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
@@ -127,7 +127,7 @@ bpftool prog pin *PROG* *FILE*
     Note: *FILE* must be located in *bpffs* mount. It must not contain a dot
     character ('.'), which is reserved for future extensions of *bpffs*.
 
-bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | name *NAME* } *MAP*] [{ offload_dev | xdpmeta_dev } *NAME*] [pinmaps *MAP_DIR*] [autoattach]
+bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | name *NAME* } *MAP*] [{ offload_dev | xdpmeta_dev } *NAME*] [pinmaps *MAP_DIR*] [autoattach] [kernel_btf *BTF_FILE*]
     Load bpf program(s) from binary *OBJ* and pin as *PATH*. **bpftool prog
     load** pins only the first program from the *OBJ* as *PATH*. **bpftool prog
     loadall** pins all programs from the *OBJ* under *PATH* directory. **type**
@@ -153,6 +153,12 @@ bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | na
     program does not support autoattach, bpftool falls back to regular pinning
     for that program instead.
 
+    The **kernel_btf** option allows specifying an external BTF file to replace
+    the system's own vmlinux BTF file for CO-RE relocations. Note that any
+    other feature relying on BTF (such as fentry/fexit programs, struct_ops)
+    requires the BTF file for the actual kernel running on the host, often
+    exposed at /sys/kernel/btf/vmlinux.
+
     Note: *PATH* must be located in *bpffs* mount. It must not contain a dot
     character ('.'), which is reserved for future extensions of *bpffs*.
 
diff --git a/tools/bpf/bpftool/bash-completion/bpftool b/tools/bpf/bpftool/bash-completion/bpftool
index 1ce409a6cbd9..27512feb5c70 100644
--- a/tools/bpf/bpftool/bash-completion/bpftool
+++ b/tools/bpf/bpftool/bash-completion/bpftool
@@ -505,13 +505,13 @@ _bpftool()
                             _bpftool_get_map_names
                             return 0
                             ;;
-                        pinned|pinmaps)
+                        pinned|pinmaps|kernel_btf)
                             _filedir
                             return 0
                             ;;
                         *)
                             COMPREPLY=( $( compgen -W "map" -- "$cur" ) )
-                            _bpftool_once_attr 'type pinmaps autoattach'
+                            _bpftool_once_attr 'type pinmaps autoattach kernel_btf'
                             _bpftool_one_of_list 'offload_dev xdpmeta_dev'
                             return 0
                             ;;
diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index f010295350be..96eea8a67225 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -1681,8 +1681,17 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 		} else if (is_prefix(*argv, "autoattach")) {
 			auto_attach = true;
 			NEXT_ARG();
+		} else if (is_prefix(*argv, "kernel_btf")) {
+			NEXT_ARG();
+
+			if (!REQ_ARGS(1))
+				goto err_free_reuse_maps;
+
+			open_opts.btf_custom_path = GET_ARG();
 		} else {
-			p_err("expected no more arguments, 'type', 'map' or 'dev', got: '%s'?",
+			p_err("expected no more arguments, "
+			      "'type', 'map', 'offload_dev', 'xdpmeta_dev', 'pinmaps', "
+			      "'autoattach', or 'kernel_btf', got: '%s'?",
 			      *argv);
 			goto err_free_reuse_maps;
 		}
@@ -2474,6 +2483,7 @@ static int do_help(int argc, char **argv)
 		"                         [map { idx IDX | name NAME } MAP]\\\n"
 		"                         [pinmaps MAP_DIR]\n"
 		"                         [autoattach]\n"
+		"                         [kernel_btf BTF_FILE]\n"
 		"       %1$s %2$s attach PROG ATTACH_TYPE [MAP]\n"
 		"       %1$s %2$s detach PROG ATTACH_TYPE [MAP]\n"
 		"       %1$s %2$s run PROG \\\n"
-- 
2.47.1

Re: [PATCH bpf-next v3] bpftool: Add support for custom BTF path in prog load/loadall

[Quentin Monnet]

2025-05-16 11:23 UTC+0800 ~ Jiayuan Chen <jiayuan.chen@linux.dev>
> This patch exposes the btf_custom_path feature to bpftool, allowing users
> to specify a custom BTF file when loading BPF programs using prog load or
> prog loadall commands.
> 
> The argument 'btf_custom_path' in libbpf is used for those kernels that
> don't have CONFIG_DEBUG_INFO_BTF enabled but still want to perform CO-RE
> relocations.
> 
> Suggested-by: Quentin Monnet <qmo@kernel.org>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
> 
> ---
> V2 -> V3: Optimized document grammar and some prompts
> https://lore.kernel.org/bpf/20250515065018.240188-1-jiayuan.chen@linux.dev/
> V1 -> V2: Added bash completion and documentation
> https://lore.kernel.org/bpf/20250513035853.75820-1-jiayuan.chen@linux.dev/
> ---
>  tools/bpf/bpftool/Documentation/bpftool-prog.rst |  8 +++++++-
>  tools/bpf/bpftool/bash-completion/bpftool        |  4 ++--
>  tools/bpf/bpftool/prog.c                         | 12 +++++++++++-
>  3 files changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
> index d6304e01afe0..4dce43e8e8a3 100644
> --- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
> +++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
> @@ -127,7 +127,7 @@ bpftool prog pin *PROG* *FILE*
>      Note: *FILE* must be located in *bpffs* mount. It must not contain a dot
>      character ('.'), which is reserved for future extensions of *bpffs*.
>  
> -bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | name *NAME* } *MAP*] [{ offload_dev | xdpmeta_dev } *NAME*] [pinmaps *MAP_DIR*] [autoattach]
> +bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | name *NAME* } *MAP*] [{ offload_dev | xdpmeta_dev } *NAME*] [pinmaps *MAP_DIR*] [autoattach] [kernel_btf *BTF_FILE*]

Woops, I just realised we also need to add kernel_btf to the command
summary at the top of the document (line 34), sorry for missing it
during the previous pass. Please add it, and mark v4 as:

    Reviewed-by: Quentin Monnet <qmo@kernel.org>

Thanks!

Re: [PATCH bpf-next v3] bpftool: Add support for custom BTF path in prog load/loadall

[Jiayuan Chen]

May 16, 2025 at 18:18, "Quentin Monnet" <qmo@kernel.org> wrote:

> 
> 2025-05-16 11:23 UTC+0800 ~ Jiayuan Chen <jiayuan.chen@linux.dev>
> 
> > 
> > This patch exposes the btf_custom_path feature to bpftool, allowing users
> > 
> >  to specify a custom BTF file when loading BPF programs using prog load or
> > 
> >  prog loadall commands.
> > 
> >  
> > 
> >  The argument 'btf_custom_path' in libbpf is used for those kernels that
> > 
> >  don't have CONFIG_DEBUG_INFO_BTF enabled but still want to perform CO-RE
> > 
> >  relocations.
> > 
> >  
> > 
> >  Suggested-by: Quentin Monnet <qmo@kernel.org>
> > 
> >  Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
> > 
> >  
> > 
> >  ---
> > 
> >  V2 -> V3: Optimized document grammar and some prompts
> > 
> >  https://lore.kernel.org/bpf/20250515065018.240188-1-jiayuan.chen@linux.dev/
> > 
> >  V1 -> V2: Added bash completion and documentation
> > 
> >  https://lore.kernel.org/bpf/20250513035853.75820-1-jiayuan.chen@linux.dev/
> > 
> >  ---
> > 
> >  tools/bpf/bpftool/Documentation/bpftool-prog.rst | 8 +++++++-
> > 
> >  tools/bpf/bpftool/bash-completion/bpftool | 4 ++--
> > 
> >  tools/bpf/bpftool/prog.c | 12 +++++++++++-
> > 
> >  3 files changed, 20 insertions(+), 4 deletions(-)
> > 
> >  
> > 
> >  diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
> > 
> >  index d6304e01afe0..4dce43e8e8a3 100644
> > 
> >  --- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
> > 
> >  +++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
> > 
> >  @@ -127,7 +127,7 @@ bpftool prog pin *PROG* *FILE*
> > 
> >  Note: *FILE* must be located in *bpffs* mount. It must not contain a dot
> > 
> >  character ('.'), which is reserved for future extensions of *bpffs*.
> > 
> >  
> > 
> >  -bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | name *NAME* } *MAP*] [{ offload_dev | xdpmeta_dev } *NAME*] [pinmaps *MAP_DIR*] [autoattach]
> > 
> >  +bpftool prog { load | loadall } *OBJ* *PATH* [type *TYPE*] [map { idx *IDX* | name *NAME* } *MAP*] [{ offload_dev | xdpmeta_dev } *NAME*] [pinmaps *MAP_DIR*] [autoattach] [kernel_btf *BTF_FILE*]
> > 
> 
> Woops, I just realised we also need to add kernel_btf to the command
> 
> summary at the top of the document (line 34), sorry for missing it

It was my mistake to miss that part. I'll prepare an updated version soon. :)

Thanks.
> during the previous pass. Please add it, and mark v4 as:
> 
>  Reviewed-by: Quentin Monnet <qmo@kernel.org>
> 
> Thanks!
>