linux-kernel - Re: [PATCH] bpf: mark get_entry_ip as __maybe

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Date:   Thu, 3 Nov 2022 16:32:47 +0100
From:   Jonas Rabenstein <rabenstein@...fau.de>
To:     stable@...r.kernel.org
Cc:     Jiri Olsa <jolsa@...nel.org>, Song Liu <song@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: mark get_entry_ip as __maybe_unused

Hi again,
after sending this out, I noticed this is only a problem in the stable
versions (starting from v6.0.3), as c09eb2e578eb1668bbc has been applied (as
03f148c159a250dd454) but not 0e253f7e558a3e250902 ("bpf: Return value in kprobe
get_func_ip only for entry address") which makes always use of get_entry_ip.
I therefore think, 0e253f7e558a3e250902 needs to be added to the stable v6.0
series as well as otherwise it can't be compiled with -Werror if
CONFIG_X6_KERNEL_IBT is set but CONFIG_FPROBE isn't.

- Jonas

On Thu, Nov 03, 2022 at 04:03:03PM +0100, Jonas Rabenstein wrote:
> Commit c09eb2e578eb1668bbc ("bpf: Adjust kprobe_multi entry_ip
> for CONFIG_X86_KERNEL_IBT") introduced the get_entry_ip() function.
> Depending on CONFIG_X86_KERNEL_IBT it is a static function or only
> a macro definition. The only user of this symbol so far is in
> kprobe_multi_link_handler() if CONFIG_FPROBE is enabled.
> If CONFIG_FROBE is not set, the symbol is not used and - depending
> on CONFIG_X86_KERNEL_IBT - a warning for get_entry_ip() is emitted.
> To solve this, the function should be marked as __maybe_unused.
> 
> Signed-off-by: Jonas Rabenstein <rabenstein@...fau.de>
> ---
>  kernel/trace/bpf_trace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index f2d8d070d024..19131aae0bc3 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1032,7 +1032,7 @@ static const struct bpf_func_proto bpf_get_func_ip_proto_tracing = {
>  };
>  
>  #ifdef CONFIG_X86_KERNEL_IBT
> -static unsigned long get_entry_ip(unsigned long fentry_ip)
> +static unsigned long __maybe_unused get_entry_ip(unsigned long fentry_ip)
>  {
>  	u32 instr;
>  
> -- 
> 2.37.4
>