RE: [PATCH bpf-next 1/2] libbpf: stop enforcing kern_version, populate it for users

[John Fastabend <john.fastabend@gmail.com>]

Andrii Nakryiko wrote:
> Kernel version enforcement for kprobes/kretprobes was removed from
> 5.0 kernel in 6c4fc209fcf9 ("bpf: remove useless version check for prog load").
> Since then, BPF programs were specifying SEC("version") just to please
> libbpf. We should stop enforcing this in libbpf, if even kernel doesn't
> care. Furthermore, libbpf now will pre-populate current kernel version
> of the host system, in case we are still running on old kernel.
> 
> This patch also removes __bpf_object__open_xattr from libbpf.h, as
> nothing in libbpf is relying on having it in that header. That function
> was never exported as LIBBPF_API and even name suggests its internal
> version. So this should be safe to remove, as it doesn't break ABI.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> ---
>  tools/lib/bpf/libbpf.c                        | 79 ++++++-------------
>  tools/lib/bpf/libbpf.h                        |  2 -
>  .../selftests/bpf/progs/test_attach_probe.c   |  1 -
>  .../bpf/progs/test_get_stack_rawtp.c          |  1 -
>  .../selftests/bpf/progs/test_perf_buffer.c    |  1 -
>  .../selftests/bpf/progs/test_stacktrace_map.c |  1 -
>  6 files changed, 22 insertions(+), 63 deletions(-)

[...]

>  static struct bpf_object *
> -__bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz,
> -		   bool needs_kver, int flags)
> +__bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
> +		   int flags)
>  {
>  	struct bpf_object *obj;
>  	int err;
> @@ -3617,7 +3585,6 @@ __bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz,
>  	CHECK_ERR(bpf_object__probe_caps(obj), err, out);
>  	CHECK_ERR(bpf_object__elf_collect(obj, flags), err, out);

If we are not going to validate the section should we also skip collect'ing it?

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e0276520171b..22a458cd602c 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1567,12 +1567,6 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
                                                       data->d_size);
                        if (err)
                                return err;
-               } else if (strcmp(name, "version") == 0) {
-                       err = bpf_object__init_kversion(obj,
-                                                       data->d_buf,
-                                                       data->d_size);
-                       if (err)
-                               return err;
                } else if (strcmp(name, "maps") == 0) {
                        obj->efile.maps_shndx = idx;
                } else if (strcmp(name, MAPS_ELF_SEC) == 0) {


>  	CHECK_ERR(bpf_object__collect_reloc(obj), err, out);
> -	CHECK_ERR(bpf_object__validate(obj, needs_kver), err, out);
>  
>  	bpf_object__elf_finish(obj);
>  	return obj;
> @@ -3626,8 +3593,8 @@ __bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz,
>  	return ERR_PTR(err);
>  }