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

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Date: Tue, 13 Feb 2024 14:08:54 -0700
From: Daniel Xu <dxu@...uu.xyz>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org, andrii@...nel.org, 
	olsajiri@...il.com, quentin@...valent.com, alan.maguire@...cle.com
Subject: Re: [PATCH bpf-next v2 0/2] bpf, bpftool: Support dumping kfunc
 prototypes from BTF

On Tue, Feb 13, 2024 at 11:09:29AM -0800, Andrii Nakryiko wrote:
> On Sun, Feb 4, 2024 at 1:06 PM Daniel Xu <dxu@...uu.xyz> wrote:
> >
> > 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
> 
> I've applied patch #1 as it's a good change regardless. Please send v2
> for patch #2.

Ack. Been a bit busy recently - will probably have time to work on this
again next weekend.