From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <olsajiri@gmail.com>
Cc: "Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
bpf@vger.kernel.org, "Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
"John Fastabend" <john.fastabend@gmail.com>,
"KP Singh" <kpsingh@chromium.org>,
"Stanislav Fomichev" <sdf@google.com>,
"Hao Luo" <haoluo@google.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Björn Töpel" <bjorn@kernel.org>,
"Steven Rostedt" <rostedt@goodmis.org>
Subject: Re: [PATCHv2 bpf-next 2/2] bpf: Move bpf_dispatcher function out of ftrace locations
Date: Fri, 2 Sep 2022 19:20:40 +0200 [thread overview]
Message-ID: <YxI7aC4L495CwZWE@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YxI1EtYjkLaooFm8@krava>
On Fri, Sep 02, 2022 at 06:53:38PM +0200, Jiri Olsa wrote:
> > Are you sure you want the notrace x86_64 only?
> >
> > That is, perhaps something like this...
> >
> > +#ifdef CONFIG_X86_64
> > +#define BPF_DISPATCHER_ATTRIBUTES __attribute__((patchable_function_entry(5)))
> > +#else
> > +#define BPF_DISPATCHER_ATTRIBUTES
> > +#endif
> > +
> > #define DEFINE_BPF_DISPATCHER(name) \
> > + notrace BPF_DISPATCHER_ATTRIBUTES \
> > noinline __nocfi unsigned int bpf_dispatcher_##name##_func( \
> >
>
> that's also an option.. but I don't this it's big deal that the function
> is traceable on other arches, because the dispatcher image is generated
> only on x86, so no other arch is touching that function entry, so it's
> safe for ftrace to attach
It just seems like a pointless difference.
From a code-gen POV you don't strictly need the notrace; without it
it'll generate:
bpf_dispatcher_name_func:
nop
nop
nop
nop
nop
call __fentry__
RET
It'll just function 'weird', but it'll 'work'.
next prev parent reply other threads:[~2022-09-02 17:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-01 13:41 [PATCHv2 bpf-next 0/2] bpf,ftrace: bpf dispatcher function fix Jiri Olsa
2022-09-01 13:41 ` [PATCHv2 bpf-next 1/2] ftrace: Add HAVE_DYNAMIC_FTRACE_NO_PATCHABLE Jiri Olsa
2022-09-01 13:41 ` [PATCHv2 bpf-next 2/2] bpf: Move bpf_dispatcher function out of ftrace locations Jiri Olsa
2022-09-02 11:14 ` Peter Zijlstra
2022-09-02 16:53 ` Jiri Olsa
2022-09-02 17:20 ` Peter Zijlstra [this message]
2022-09-03 13:11 ` Jiri Olsa
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