Re: [PATCH bpf-next v3 0/3] Annotate kfuncs in .BTF_ids section

From: Jiri Olsa <olsajiri@gmail.com>
To: Daniel Xu <dxu@dxuuu.xyz>
Cc: Jiri Olsa <olsajiri@gmail.com>,
	linux-input@vger.kernel.org, coreteam@netfilter.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org,
	linux-kselftest@vger.kernel.org,
	linux-trace-kernel@vger.kernel.org, fsverity@lists.linux.dev,
	bpf@vger.kernel.org, netdev@vger.kernel.org,
	linux-stm32@st-md-mailman.stormreply.com,
	cgroups@vger.kernel.org, alexei.starovoitov@gmail.com,
	quentin@isovalent.com, alan.maguire@oracle.com, memxor@gmail.com
Subject: Re: [PATCH bpf-next v3 0/3] Annotate kfuncs in .BTF_ids section
Date: Sat, 13 Jan 2024 14:57:40 +0100	[thread overview]
Message-ID: <ZaKW1AghwUnVz_c4@krava> (raw)
In-Reply-To: <2dhmwvfnnqnlrui2qcr5fob54gdsuse5caievct42trvvia6qe@p24nymz3uttv>

On Fri, Jan 12, 2024 at 01:03:59PM -0700, Daniel Xu wrote:
> On Fri, Jan 12, 2024 at 05:20:39PM +0100, Jiri Olsa wrote:
> > On Sat, Jan 06, 2024 at 11:24:07AM -0700, Daniel Xu wrote:
> > > === Description ===
> > > 
> > > This is a bpf-treewide change that annotates all kfuncs as such inside
> > > .BTF_ids. This annotation eventually allows us to automatically generate
> > > kfunc prototypes from bpftool.
> > > 
> > > We store this metadata inside a yet-unused flags field inside struct
> > > btf_id_set8 (thanks Kumar!). pahole will be taught where to look.
> > > 
> > > More details about the full chain of events are available in commit 3's
> > > description.
> > > 
> > > The accompanying pahole changes (still needs some cleanup) can be viewed
> > > here on this "frozen" branch [0].
> > 
> > so the plan is to have bpftool support to generate header file
> > with detected kfuncs?
> 
> Yep, that's the major use case. But I see other use cases as well like

ok, any chance you could already include it in the patchset?
would be a great way to test this.. maybe we could change
selftests to use that

thanks,
jirka

> precision probing of kfuncs. Rather than guess and check which progs can
> load (in the event of backwards incompatible kfunc changes), programs
> can look at kfunc type signature thru BTF.