linux-kernel - Re: [PATCH bpf-next 2/2] selftests/bpf: Add test to access const void pointer argument in tracing program

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Message-ID: <CALqUS-7Jh2MpBTjQ9GNfRZKjUqg1t3n-OT_GYQqH=0TmkXoc0A@mail.gmail.com>
Date: Tue, 15 Apr 2025 22:31:46 +0800
From: Kafai Wan <mannkafai@...il.com>
To: Jiri Olsa <olsajiri@...il.com>
Cc: martin.lau@...ux.dev, ast@...nel.org, daniel@...earbox.net, 
	andrii@...nel.org, eddyz87@...il.com, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, mykolal@...com, shuah@...nel.org, 
	memxor@...il.com, bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, kafai.wan@...mail.com, leon.hwang@...ux.dev
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: Add test to access const void
 pointer argument in tracing program

On Mon, Apr 14, 2025 at 6:35 PM Jiri Olsa <olsajiri@...il.com> wrote:
>
> On Sun, Apr 13, 2025 at 01:06:26AM +0800, KaFai Wan wrote:
> > Adding verifier test for accessing const void pointer argument in
> > tracing programs.
> >
> > The test program loads 2nd argument of kfree tp_btf which is
> > const void pointer and checks that verifier allows that.
> >
> > Signed-off-by: KaFai Wan <kafai.wan@...mail.com>
> > ---
> >  .../selftests/bpf/progs/verifier_btf_ctx_access.c        | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/tools/testing/selftests/bpf/progs/verifier_btf_ctx_access.c b/tools/testing/selftests/bpf/progs/verifier_btf_ctx_access.c
> > index 28b939572cda..a6cec7f73dcd 100644
> > --- a/tools/testing/selftests/bpf/progs/verifier_btf_ctx_access.c
> > +++ b/tools/testing/selftests/bpf/progs/verifier_btf_ctx_access.c
> > @@ -65,4 +65,13 @@ __naked void ctx_access_u32_pointer_reject_8(void)
> >  "    ::: __clobber_all);
> >  }
> >
> > +SEC("tp_btf/kfree")
> > +__description("btf_ctx_access const void pointer accept")
> > +int ctx_access_const_void_pointer_accept(void)
> > +{
> > +     /* load 2nd argument value (const void pointer) */
> > +     asm volatile ("r2 = *(u64 *)(r1 + 8); ");
>
> I think we should follow formatting of other tests in the file,
> a do smth like:
>
>         asm volatile ("                         \
>         r2 = *(u64 *)(r1 + 8); ");   /* load 2nd argument value (const void pointer) */\
>         ...

I will fix it. and I find out the kernel does not support test_run of tp_btf, I
will change to fentry.

>
> thanks,
> jirka
>
>
> > +     return 0;
> > +}
> > +
> >  char _license[] SEC("license") = "GPL";
> > --
> > 2.43.0
> >

thanks,
kafai