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From: Jiri Olsa <jolsa@redhat.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <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>
Subject: Re: [PATCH bpf-next 06/29] bpf: Add bpf_arg/bpf_ret_value helpers for tracing programs
Date: Sun, 28 Nov 2021 19:07:05 +0100	[thread overview]
Message-ID: <YaPFSesoR0uiU9DU@krava> (raw)
In-Reply-To: <CAADnVQLx_-GuCeE5S3KV5g+YsDfQaFS_BZ8qDCN72gYFLXjj6A@mail.gmail.com>

On Thu, Nov 25, 2021 at 09:14:15AM -0700, Alexei Starovoitov wrote:
> On Wed, Nov 24, 2021 at 2:43 PM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> > > +               /* Implement bpf_arg inline. */
> > > +               if (prog_type == BPF_PROG_TYPE_TRACING &&
> > > +                   insn->imm == BPF_FUNC_arg) {
> > > +                       /* Load nr_args from ctx - 8 */
> > > +                       insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
> > > +                       insn_buf[1] = BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 4);
> > > +                       insn_buf[2] = BPF_ALU64_IMM(BPF_MUL, BPF_REG_2, 8);
> > > +                       insn_buf[3] = BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1);
> > > +                       insn_buf[4] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 0);
> > > +                       insn_buf[5] = BPF_JMP_A(1);
> > > +                       insn_buf[6] = BPF_MOV64_IMM(BPF_REG_0, 0);
> > > +
> > > +                       new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 7);
> > > +                       if (!new_prog)
> > > +                               return -ENOMEM;
> > > +
> > > +                       delta    += 6;
> > > +                       env->prog = prog = new_prog;
> > > +                       insn      = new_prog->insnsi + i + delta;
> > > +                       continue;
> >
> > nit: this whole sequence of steps and calculations seems like
> > something that might be abstracted and hidden behind a macro or helper
> > func? Not related to your change, though. But wouldn't it be easier to
> > understand if it was just written as:
> >
> > PATCH_INSNS(
> >     BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
> >     BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 4);
> >     BPF_ALU64_IMM(BPF_MUL, BPF_REG_2, 8);
> >     BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1);
> >     BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 0);
> >     BPF_JMP_A(1);
> >     BPF_MOV64_IMM(BPF_REG_0, 0));
> 
> Daniel and myself tried to do similar macro magic in the past,
> but it suffers unnecessary stack increase and extra copies.
> So eventually we got rid of it.
> I suggest staying with Jiri's approach.
> 
> Independent from anything else...
> Just noticed BPF_MUL in the above...
> Please use BPF_LSH instead. JITs don't optimize such things.
> It's a job of gcc/llvm to do so. JITs assume that all
> normal optimizations were done by the compiler.
> 

will change

thanks,
jirka


  reply	other threads:[~2021-11-28 18:09 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-18 11:24 [RFC bpf-next v5 00/29] bpf: Add batch support for attaching trampolines Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 01/29] ftrace: Use direct_ops hash in unregister_ftrace_direct Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 02/29] ftrace: Add cleanup to unregister_ftrace_direct_multi Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 03/29] ftrace: Add ftrace_set_filter_ips function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 04/29] bpf: Factor bpf_check_attach_target function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 05/29] bpf: Add bpf_check_attach_model function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 06/29] bpf: Add bpf_arg/bpf_ret_value helpers for tracing programs Jiri Olsa
2021-11-24 21:43   ` Andrii Nakryiko
2021-11-25 16:14     ` Alexei Starovoitov
2021-11-28 18:07       ` Jiri Olsa [this message]
2021-11-28 18:06     ` Jiri Olsa
2021-12-01  7:13       ` Andrii Nakryiko
2021-12-01 17:37         ` Alexei Starovoitov
2021-12-01 17:59           ` Andrii Nakryiko
2021-12-01 20:36             ` Alexei Starovoitov
2021-12-01 21:16             ` Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 07/29] bpf, x64: Allow to use caller address from stack Jiri Olsa
2021-11-19  4:14   ` Alexei Starovoitov
2021-11-19 21:46     ` Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 08/29] bpf: Keep active attached trampoline in bpf_prog Jiri Olsa
2021-11-24 21:48   ` Andrii Nakryiko
2021-11-28 17:24     ` Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 09/29] bpf: Add support to load multi func tracing program Jiri Olsa
2021-11-19  4:11   ` Alexei Starovoitov
2021-11-22 20:15     ` Jiri Olsa
2021-11-24 21:51       ` Andrii Nakryiko
2021-11-28 17:41         ` Jiri Olsa
2021-12-01  7:17           ` Andrii Nakryiko
2021-12-01 21:20             ` Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 10/29] bpf: Add bpf_trampoline_id object Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 11/29] bpf: Add addr to " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 12/29] bpf: Add struct bpf_tramp_node layer Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 13/29] bpf: Add bpf_tramp_attach layer for trampoline attachment Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 14/29] bpf: Add support to store multiple ids in bpf_tramp_id object Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 15/29] bpf: Add support to store multiple addrs " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 16/29] bpf: Add bpf_tramp_id_single function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 17/29] bpf: Resolve id in bpf_tramp_id_single Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 18/29] bpf: Add refcount_t to struct bpf_tramp_id Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 19/29] bpf: Add support to attach trampolines with multiple IDs Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 20/29] bpf: Add support for tracing multi link Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 21/29] libbpf: Add btf__find_by_glob_kind function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 22/29] libbpf: Add support to link multi func tracing program Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 23/29] selftests/bpf: Add bpf_arg/bpf_ret_value test Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 24/29] selftests/bpf: Add fentry multi func test Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 25/29] selftests/bpf: Add fexit " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 26/29] selftests/bpf: Add fentry/fexit " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 27/29] selftests/bpf: Add mixed " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 28/29] selftests/bpf: Add ret_mod " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 29/29] selftests/bpf: Add attach " Jiri Olsa

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