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    SubjectRe: [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@gmail.com> wrote:
    >
    > On Wed, Feb 2, 2022 at 5:53 AM Jiri Olsa <jolsa@redhat.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@kernel.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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