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 <olsajiri@gmail.com>]

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@kernel.org> 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@redhat.com>
> > 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


---
From b12aea55f1171dc09cde2957f9019c84bda7adbb Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Fri, 5 May 2023 13:28:46 +0200
Subject: [PATCH] perf tools: Fix lock_contention bpf program

We need to define empty 'struct rq' so the runqueues gets
resolved properly:

  # ./perf lock con -b
  libbpf: extern (var ksym) 'runqueues': incompatible types, expected [99] fwd rq, but kernel has [19783] struct rq
  libbpf: failed to load object 'lock_contention_bpf'
  libbpf: failed to load BPF skeleton 'lock_contention_bpf': -22
  Failed to load lock-contention BPF skeleton

Also rq__old/rq__new need additional '_' so the suffix is ignored
properly.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/perf/util/bpf_skel/lock_contention.bpf.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
index 8911e2a077d8..c2bf24c68c14 100644
--- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
+++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
@@ -416,13 +416,15 @@ int contention_end(u64 *ctx)
 	return 0;
 }
 
+struct rq {};
+
 extern struct rq runqueues __ksym;
 
-struct rq__old {
+struct rq___old {
 	raw_spinlock_t lock;
 } __attribute__((preserve_access_index));
 
-struct rq__new {
+struct rq___new {
 	raw_spinlock_t __lock;
 } __attribute__((preserve_access_index));
 
@@ -434,8 +436,8 @@ int BPF_PROG(collect_lock_syms)
 
 	for (int i = 0; i < MAX_CPUS; i++) {
 		struct rq *rq = bpf_per_cpu_ptr(&runqueues, i);
-		struct rq__new *rq_new = (void *)rq;
-		struct rq__old *rq_old = (void *)rq;
+		struct rq___new *rq_new = (void *)rq;
+		struct rq___old *rq_old = (void *)rq;
 
 		if (rq == NULL)
 			break;
-- 
2.40.1