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Date: Mon, 7 Feb 2022 13:01:29 -0800 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Andrii Nakryiko <andrii.nakryiko@...il.com> Cc: Jiri Olsa <jolsa@...hat.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>, Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...omium.org>, Steven Rostedt <rostedt@...dmis.org>, Jiri Olsa <olsajiri@...il.com> Subject: Re: [PATCH 2/8] bpf: Add bpf_get_func_ip kprobe helper for fprobe link On Mon, Feb 7, 2022 at 10:59 AM Andrii Nakryiko <andrii.nakryiko@...il.com> wrote: > > On Wed, Feb 2, 2022 at 5:53 AM Jiri Olsa <jolsa@...hat.com> wrote: > > > > Adding support to call get_func_ip_fprobe helper from kprobe > > programs attached by fprobe link. > > > > Also adding support to inline it, because it's single load > > instruction. > > > > Signed-off-by: Jiri Olsa <jolsa@...nel.org> > > --- > > kernel/bpf/verifier.c | 19 ++++++++++++++++++- > > kernel/trace/bpf_trace.c | 16 +++++++++++++++- > > 2 files changed, 33 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index 1ae41d0cf96c..a745ded00635 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -13625,7 +13625,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env) > > continue; > > } > > > > - /* Implement bpf_get_func_ip inline. */ > > + /* Implement tracing bpf_get_func_ip inline. */ > > if (prog_type == BPF_PROG_TYPE_TRACING && > > insn->imm == BPF_FUNC_get_func_ip) { > > /* Load IP address from ctx - 16 */ > > @@ -13640,6 +13640,23 @@ static int do_misc_fixups(struct bpf_verifier_env *env) > > continue; > > } > > > > + /* Implement kprobe/fprobe bpf_get_func_ip inline. */ > > + if (prog_type == BPF_PROG_TYPE_KPROBE && > > + eatype == BPF_TRACE_FPROBE && > > + insn->imm == BPF_FUNC_get_func_ip) { > > + /* Load IP address from ctx (struct pt_regs) ip */ > > + insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, > > + offsetof(struct pt_regs, ip)); > > Isn't this architecture-specific? I'm starting to dislike this > inlining whole more and more. It's just a complication in verifier > without clear real-world benefits. We are clearly prematurely > optimizing here. In practice you'll just call bpf_get_func_ip() once > and that's it. Function call overhead will be negligible compare to > other *userful* work you'll be doing in your BPF program. We should be doing inlining when we can. Every bit of performance matters.
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