Re: [PATCH RFC/RFT] perf bpf skels: Stop using vmlinux.h generated from BTF, use subset of used structs + CO-RE. was Re: BPF skels in perf .Re: [GIT PULL] perf tools changes for v6.4

[Jiri Olsa]

On Fri, May 05, 2023 at 10:04:47AM -0700, Ian Rogers wrote:
> On Fri, May 5, 2023 at 9:56 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
> >
> > Em Fri, May 05, 2023 at 10:33:15AM -0300, Arnaldo Carvalho de Melo escreveu:
> > > Em Fri, May 05, 2023 at 01:03:14AM +0200, Jiri Olsa escreveu:
> > > That with the preserve_access_index isn't needed, we need just the
> > > fields that we access in the tools, right?
> >
> > I'm now doing build test this in many distro containers, without the two
> > reverts, i.e. BPF skels continue as opt-out as in my pull request, to
> > test build and also for the functionality tests on the tools using such
> > bpf skels, see below, no touching of vmlinux nor BTF data during the
> > build.
> >
> > - Arnaldo
> >
> > From 882adaee50bc27f85374aeb2fbaa5b76bef60d05 Mon Sep 17 00:00:00 2001
> > From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > Date: Thu, 4 May 2023 19:03:51 -0300
> > Subject: [PATCH 1/1] perf bpf skels: Stop using vmlinux.h generated from BTF,
> >  use subset of used structs + CO-RE
> >
> > Linus reported a build break due to using a vmlinux without a BTF elf
> > section to generate the vmlinux.h header with bpftool for use in the BPF
> > tools in tools/perf/util/bpf_skel/*.bpf.c.
> >
> > Instead add a vmlinux.h file with the structs needed with the fields the
> > tools need, marking the structs with __attribute__((preserve_access_index)),
> > so that libbpf's CO-RE code can fixup the struct field offsets.
> >
> > In some cases the vmlinux.h file that was being generated by bpftool
> > from the kernel BTF information was not needed at all, just including
> > linux/bpf.h, sometimes linux/perf_event.h was enough as non-UAPI
> > types were not being used.
> >
> > To keep te patch small, include those UAPI headers from the trimmed down
> > vmlinux.h file, that then provides the tools with just the structs and
> > the subset of its fields needed for them.
> >
> > Testing it:
> >
> >   # perf lock contention -b find / > /dev/null

I tested perf lock con -abv -L rcu_state sleep 1
and needed fix below

jirka


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