[PATCH v3] bpf, libbpf: use valid btf in bpf_program__set_attach_target

[PATCH v3] bpf, libbpf: use valid btf in bpf_program__set_attach_target

[Luigi Rizzo]

bpf_program__set_attach_target(prog, fd, ...) will always fail when
fd = 0 (attach to a kernel symbol) because obj->btf_vmlinux is NULL
and there is no way to set it (at the moment btf_vmlinux is meant
to be temporary storage for use in bpf_object__load_xattr()).

Fix this by using libbpf_find_vmlinux_btf_id().

At some point we may want to opportunistically cache btf_vmlinux
so it can be reused with multiple programs.

Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Luigi Rizzo <lrizzo@google.com>
---
 tools/lib/bpf/libbpf.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a4f55f8a460d..33bf102259dd 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10353,9 +10353,8 @@ int bpf_program__set_attach_target(struct bpf_program *prog,
 		btf_id = libbpf_find_prog_btf_id(attach_func_name,
 						 attach_prog_fd);
 	else
-		btf_id = __find_vmlinux_btf_id(prog->obj->btf_vmlinux,
-					       attach_func_name,
-					       prog->expected_attach_type);
+		btf_id = libbpf_find_vmlinux_btf_id(attach_func_name,
+						    prog->expected_attach_type);
 
 	if (btf_id < 0)
 		return btf_id;
-- 
2.28.0.806.g8561365e88-goog

Re: [PATCH v3] bpf, libbpf: use valid btf in bpf_program__set_attach_target

[Petar Penkov]

On Mon, Oct 5, 2020 at 3:45 PM Luigi Rizzo <lrizzo@google.com> wrote:
>
> bpf_program__set_attach_target(prog, fd, ...) will always fail when
> fd = 0 (attach to a kernel symbol) because obj->btf_vmlinux is NULL
> and there is no way to set it (at the moment btf_vmlinux is meant
> to be temporary storage for use in bpf_object__load_xattr()).
>
> Fix this by using libbpf_find_vmlinux_btf_id().
>
> At some point we may want to opportunistically cache btf_vmlinux
> so it can be reused with multiple programs.
>
> Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Petar Penkov <ppenkov@google.com>
> Signed-off-by: Luigi Rizzo <lrizzo@google.com>
> ---
>  tools/lib/bpf/libbpf.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index a4f55f8a460d..33bf102259dd 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -10353,9 +10353,8 @@ int bpf_program__set_attach_target(struct bpf_program *prog,
>                 btf_id = libbpf_find_prog_btf_id(attach_func_name,
>                                                  attach_prog_fd);
>         else
> -               btf_id = __find_vmlinux_btf_id(prog->obj->btf_vmlinux,
> -                                              attach_func_name,
> -                                              prog->expected_attach_type);
> +               btf_id = libbpf_find_vmlinux_btf_id(attach_func_name,
> +                                                   prog->expected_attach_type);
>
>         if (btf_id < 0)
>                 return btf_id;
> --
> 2.28.0.806.g8561365e88-goog
>

Re: [PATCH v3] bpf, libbpf: use valid btf in bpf_program__set_attach_target

[patchwork-bot+bpf]

Hello:

This patch was applied to bpf/bpf-next.git (refs/heads/master):

On Mon,  5 Oct 2020 15:45:28 -0700 you wrote:
> bpf_program__set_attach_target(prog, fd, ...) will always fail when
> fd = 0 (attach to a kernel symbol) because obj->btf_vmlinux is NULL
> and there is no way to set it (at the moment btf_vmlinux is meant
> to be temporary storage for use in bpf_object__load_xattr()).
> 
> Fix this by using libbpf_find_vmlinux_btf_id().
> 
> [...]

Here is the summary with links:
  - [v3] bpf, libbpf: use valid btf in bpf_program__set_attach_target
    https://git.kernel.org/bpf/bpf-next/c/8cee9107e72c

You are awesome, thank you!
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