Re: [RFC bpf-next 0/5] bpf, x86: Add bpf_get_func_ip helper

From: Alan Maguire <alan.maguire@oracle.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andriin@fb.com>,
	netdev@vger.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>,
	Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [RFC bpf-next 0/5] bpf, x86: Add bpf_get_func_ip helper
Date: Thu, 1 Jul 2021 18:22:45 +0100 (IST)	[thread overview]
Message-ID: <alpine.LRH.2.23.451.2107011819160.27594@localhost> (raw)
In-Reply-To: <20210629192945.1071862-1-jolsa@kernel.org>

On Tue, 29 Jun 2021, Jiri Olsa wrote:

> hi,
> adding bpf_get_func_ip helper that returns IP address of the
> caller function for trampoline and krobe programs.
> 
> There're 2 specific implementation of the bpf_get_func_ip
> helper, one for trampoline progs and one for kprobe/kretprobe
> progs.
> 
> The trampoline helper call is replaced/inlined by verifier
> with simple move instruction. The kprobe/kretprobe is actual
> helper call that returns prepared caller address.
> 
> The trampoline extra 3 instructions for storing IP address
> is now optional, which I'm not completely sure is necessary,
> so I plan to do some benchmarks, if it's noticeable, hence
> the RFC. I'm also not completely sure about the kprobe/kretprobe
> implementation.
> 
> Also available at:
>   https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   bpf/get_func_ip
> 
> thanks,
> jirka
> 
>

This is great Jiri! Feel free to add for the series:

Tested-by: Alan Maguire <alan.maguire@oracle.com>

BTW I also verified that if we extend bpf_program__attach_kprobe() to
support the function+offset format in the func_name argument for kprobes, 
the following test will pass too:

__u64 test5_result = 0;
SEC("kprobe/bpf_fentry_test5+0x6")
int test5(struct pt_regs *ctx)
{
        __u64 addr = bpf_get_func_ip(ctx);

        test5_result = (const void *) addr == (&bpf_fentry_test5 + 0x6);
        return 0;
}

Thanks!

Alan

> ---
> Jiri Olsa (5):
>       bpf, x86: Store caller's ip in trampoline stack
>       bpf: Enable BPF_TRAMP_F_IP_ARG for trampolines with call_get_func_ip
>       bpf: Add bpf_get_func_ip helper for tracing programs
>       bpf: Add bpf_get_func_ip helper for kprobe programs
>       selftests/bpf: Add test for bpf_get_func_ip helper
> 
>  arch/x86/net/bpf_jit_comp.c                               | 19 +++++++++++++++++++
>  include/linux/bpf.h                                       |  5 +++++
>  include/linux/filter.h                                    |  3 ++-
>  include/uapi/linux/bpf.h                                  |  7 +++++++
>  kernel/bpf/trampoline.c                                   | 12 +++++++++---
>  kernel/bpf/verifier.c                                     | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  kernel/trace/bpf_trace.c                                  | 29 +++++++++++++++++++++++++++++
>  kernel/trace/trace_kprobe.c                               | 20 ++++++++++++++++++--
>  kernel/trace/trace_probe.h                                |  5 +++++
>  tools/include/uapi/linux/bpf.h                            |  7 +++++++
>  tools/testing/selftests/bpf/prog_tests/get_func_ip_test.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  tools/testing/selftests/bpf/progs/get_func_ip_test.c      | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  12 files changed, 260 insertions(+), 6 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/get_func_ip_test.c
>  create mode 100644 tools/testing/selftests/bpf/progs/get_func_ip_test.c
> 
> 