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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Jiong Wang <jiong.wang@netronome.com>
Cc: daniel@iogearbox.net, bpf@vger.kernel.org,
	netdev@vger.kernel.org, oss-drivers@netronome.com
Subject: Re: [PATCH v6 bpf-next 04/17] bpf: introduce new alu insn BPF_ZEXT for explicit zero extension
Date: Mon, 6 May 2019 08:57:06 -0700	[thread overview]
Message-ID: <20190506155704.4t7xy3mqer4eps3y@ast-mbp> (raw)
In-Reply-To: <1556880164-10689-5-git-send-email-jiong.wang@netronome.com>

On Fri, May 03, 2019 at 11:42:31AM +0100, Jiong Wang wrote:
> This patch introduce new alu32 insn BPF_ZEXT, and allocate the unused
> opcode 0xe0 to it.
> 
> Compared with the other alu32 insns, zero extension on low 32-bit is the
> only semantics for this instruction. It also allows various JIT back-ends
> to do optimal zero extension code-gen.
> 
> BPF_ZEXT is supposed to be encoded with BPF_ALU only, and is supposed to be
> generated by the latter 32-bit optimization code inside verifier for those
> arches that do not support hardware implicit zero extension only.
> 
> It is not supposed to be used in user's program directly at the moment.
> Therefore, no need to recognize it inside generic verification code. It
> just need to be supported for execution on interpreter or related JIT
> back-ends.

uapi and the doc define it, but "it is not supposed to be used" ?!

> Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
> ---
>  Documentation/networking/filter.txt | 10 ++++++++++
>  include/uapi/linux/bpf.h            |  3 +++
>  kernel/bpf/core.c                   |  4 ++++
>  tools/include/uapi/linux/bpf.h      |  3 +++
>  4 files changed, 20 insertions(+)
> 
> diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
> index 319e5e0..1cb3e42 100644
> --- a/Documentation/networking/filter.txt
> +++ b/Documentation/networking/filter.txt
> @@ -903,6 +903,16 @@ If BPF_CLASS(code) == BPF_ALU or BPF_ALU64 [ in eBPF ], BPF_OP(code) is one of:
>    BPF_MOV   0xb0  /* eBPF only: mov reg to reg */
>    BPF_ARSH  0xc0  /* eBPF only: sign extending shift right */
>    BPF_END   0xd0  /* eBPF only: endianness conversion */
> +  BPF_ZEXT  0xe0  /* eBPF BPF_ALU only: zero-extends low 32-bit */
> +
> +Compared with BPF_ALU | BPF_MOV which zero-extends low 32-bit implicitly,
> +BPF_ALU | BPF_ZEXT zero-extends low 32-bit explicitly. Such zero extension is

wait. that's an excellent observation. alu|mov is exactly it.
we do not need another insn.
we probably can teach the verifier to recognize <<32, >>32 and replace with mov32


  reply	other threads:[~2019-05-06 15:57 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-03 10:42 [PATCH v6 bpf-next 00/17] bpf: eliminate zero extensions for sub-register writes Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 01/17] bpf: verifier: offer more accurate helper function arg and return type Jiong Wang
2019-05-06 13:57   ` Daniel Borkmann
2019-05-06 22:25     ` Jiong Wang
2019-05-08 11:12       ` Jiong Wang
2019-05-06 15:50   ` Alexei Starovoitov
2019-05-08 14:45     ` Jiong Wang
2019-05-08 17:51       ` Alexei Starovoitov
2019-05-09 12:32         ` Jiong Wang
2019-05-09 17:31           ` Jiong Wang
2019-05-10  1:53           ` Alexei Starovoitov
2019-05-10  8:30             ` Jiong Wang
2019-05-10 20:10               ` Alexei Starovoitov
2019-05-10 21:59                 ` Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 02/17] bpf: verifier: mark verified-insn with sub-register zext flag Jiong Wang
2019-05-06 13:49   ` Daniel Borkmann
2019-05-06 14:49     ` Daniel Borkmann
2019-05-06 22:14     ` Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 03/17] bpf: verifier: mark patched-insn " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 04/17] bpf: introduce new alu insn BPF_ZEXT for explicit zero extension Jiong Wang
2019-05-06 15:57   ` Alexei Starovoitov [this message]
2019-05-06 23:19     ` Jiong Wang
2019-05-07  4:29       ` Jiong Wang
2019-05-07  4:40         ` Alexei Starovoitov
2019-05-03 10:42 ` [PATCH v6 bpf-next 05/17] bpf: verifier: insert BPF_ZEXT according to zext analysis result Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 06/17] bpf: introduce new bpf prog load flags "BPF_F_TEST_RND_HI32" Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 07/17] bpf: verifier: randomize high 32-bit when BPF_F_TEST_RND_HI32 is set Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 08/17] libbpf: add "prog_flags" to bpf_program/bpf_prog_load_attr/bpf_load_program_attr Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 09/17] selftests: bpf: adjust several test_verifier helpers for insn insertion Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 10/17] selftests: bpf: enable hi32 randomization for all tests Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 11/17] arm: bpf: eliminate zero extension code-gen Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 12/17] powerpc: " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 13/17] s390: " Jiong Wang
2019-05-03 13:41   ` Heiko Carstens
2019-05-03 13:50     ` Eric Dumazet
2019-05-03 14:09     ` Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 14/17] sparc: " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 15/17] x32: " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 16/17] riscv: " Jiong Wang
2019-05-03 10:42 ` [PATCH v6 bpf-next 17/17] nfp: " Jiong Wang

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