[PATCH bpf-next v2 0/2] bpf, bpftool: Support dumping kfunc prototypes from BTF

[Daniel Xu <dxu@dxuuu.xyz>]

This patchset enables dumping kfunc prototypes from bpftool. This is
useful b/c with this patchset, end users will no longer have to manually
define kfunc prototypes. For the kernel tree, this also means we can
drop kfunc prototypes from:

        tools/testing/selftests/bpf/bpf_kfuncs.h
        tools/testing/selftests/bpf/bpf_experimental.h

Example usage:

        $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux

        $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
        extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
        extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
        extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;

Note that this patchset is only effective after the enabling pahole [0]
change is merged and the resulting feature enabled with
--btf_features=decl_tag_kfuncs.

[0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/

=== Changelog ===

From v1:
* Add __weak annotation
* Use btf_dump for kfunc prototypes
* Update kernel bpf_rdonly_cast() signature

Daniel Xu (2):
  bpf: Have bpf_rdonly_cast() take a const pointer
  bpftool: Support dumping kfunc prototypes from BTF

 kernel/bpf/helpers.c    |  4 ++--
 tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 2 deletions(-)

-- 
2.42.1