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: <Z_zk4kg_qQviauLE@krava>
Date: Mon, 14 Apr 2025 12:35:14 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: KaFai Wan <mannkafai@...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 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) */\
	...

thanks,
jirka


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