From dthaler1968@googlemail.com Fri Jan 26 14:27:19 2024 Return-Path: X-Original-To: bpf@ietfa.amsl.com Delivered-To: bpf@ietfa.amsl.com Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id E7238C14F705 for ; Fri, 26 Jan 2024 14:27:19 -0800 (PST) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -6.856 X-Spam-Level: X-Spam-Status: No, score=-6.856 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_HI=-5, RCVD_IN_ZEN_BLOCKED_OPENDNS=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01, URIBL_DBL_BLOCKED_OPENDNS=0.001, URIBL_ZEN_BLOCKED_OPENDNS=0.001] autolearn=ham autolearn_force=no Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=googlemail.com Received: from mail.ietf.org ([50.223.129.194]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 6yYOXJ5Gyu3V for ; Fri, 26 Jan 2024 14:27:16 -0800 (PST) Received: from mail-pg1-x52c.google.com (mail-pg1-x52c.google.com [IPv6:2607:f8b0:4864:20::52c]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 1CC27C14F704 for ; Fri, 26 Jan 2024 14:27:16 -0800 (PST) Received: by mail-pg1-x52c.google.com with SMTP id 41be03b00d2f7-5ce2aada130so601287a12.1 for ; Fri, 26 Jan 2024 14:27:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=20230601; t=1706308035; x=1706912835; darn=ietf.org; h=content-language:thread-index:content-transfer-encoding :mime-version:message-id:date:subject:in-reply-to:references:cc:to :from:from:to:cc:subject:date:message-id:reply-to; bh=jUtFzxEXad4F85Weuilo5A/gdxKABzI+tPFWTtBxOPQ=; b=EiLffAHXAqQ5qA92EDkW2/f1jvsHYJl1b06SkTvuaOvyFy79dsG08BSNWINam3HLee siHix99EJBwgWcbokgnmxyL631mV64KOy1e4n7gubHOHseC+6EFnUdLeVBFlvcBiZQm9 /Pk/Kgq4TUpCb4gLR2WtP3BR0s6A6bs1fjiVbBdOxwnyw/ot2NYEQKUzmoHa6tTa1Bvi mo5BAMNtlM4GHbgQjRQaUyEb3KoIh5y/yZ9sL74xpn24kW/jAUnEJ+Fu5hJPORG0VSLx XCOTWKhRz3WI3QshqPUXrBP0IsrHJzxDVOI9FMuSqPyV7kSfpMVloOMXMyYUQ83GB/l6 B4Pw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1706308035; x=1706912835; h=content-language:thread-index:content-transfer-encoding :mime-version:message-id:date:subject:in-reply-to:references:cc:to :from:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=jUtFzxEXad4F85Weuilo5A/gdxKABzI+tPFWTtBxOPQ=; b=n2kSiAO3FowXs70GsPbrvNw46IiY8AlNKCc7vZCjGTVeHjrYHqwTsBd/LIQlm3E6v3 FpG6GgkZcUEHGHkV4NjKN84tuFCMdcPfr281QRm7ncqx8uj9JWJEk9g3OUHkTQDZFbOv BzLOdno0uHMtgfNRYNyF/GTnVvK6AcBZZHPzhpDUnTGmPUET3XujlbxSmcNa/TXqznqz e8wfX3J9zmGqxNGwHsLTo9H4yh7+ZRUsH1jAgboHwuBk5W7bBytSAWc+53Hd3sGp5s+Z LzpUJR6buB4mMQ48sUGw7cDi5Ul5MTgMBoc3WTuuTu46SsGu+OryG7VIY7paSMZbvTjP CrHw== X-Gm-Message-State: AOJu0Yz7uvEVcXnMWwdS6yBin0uBCCKjLftXVFz/j/SSVcD2HxsgMmnB BCcnDKOhoA2/z/jEd2qqMskRU5A/kLpr/TzkZFrhj5uhK01uRkxSNuh1YvuKIKg= X-Google-Smtp-Source: AGHT+IGQVfPtPOMLv9m7WEb+mB6I/8QNfvyBUXlevIiFsSKZADnKJVPY/lx1aavFbXx8t0dFHuH3CQ== X-Received: by 2002:a17:90a:1fcc:b0:290:1464:e994 with SMTP id z12-20020a17090a1fcc00b002901464e994mr509579pjz.46.1706308035092; Fri, 26 Jan 2024 14:27:15 -0800 (PST) Received: from ArmidaleLaptop (c-67-170-74-237.hsd1.wa.comcast.net. [67.170.74.237]) by smtp.gmail.com with ESMTPSA id c92-20020a17090a496500b0029102d936casm4034619pjh.47.2024.01.26.14.27.14 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Jan 2024 14:27:14 -0800 (PST) From: dthaler1968@googlemail.com X-Google-Original-From: To: "'Yonghong Song'" Cc: , References: <085f01da48bb$fe0c3cb0$fa24b610$@gmail.com> <08ab01da48be$603541a0$209fc4e0$@gmail.com> <829aa552-b04e-4f08-9874-b3f929741852@linux.dev> <095f01da48e8$611687d0$23439770$@gmail.com> <4dfb0d6a-aa48-4d96-82f0-09a960b1012f@linux.dev> <1fc001da4e6a$2848cad0$78da6070$@gmail.com> <9d077ed4-6a30-49db-8160-83d8c525ff3e@linux.dev> <259a01da4ff4$adfe9c50$09fbd4f0$@gmail.com> In-Reply-To: Date: Fri, 26 Jan 2024 14:27:10 -0800 Message-ID: <294f01da50a6$ce3d0670$6ab71350$@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook 16.0 Thread-Index: AQGkwaT1bS2nmU/D6EzqCIA6r6THFAGlkngPAiWOVp0CBJjXigIgg/ivAZjEuOEC/rKUjQJO4XhxARE1PEaw2ImpwA== Content-Language: en-us Archived-At: Subject: Re: [Bpf] 64-bit immediate instructions clarification X-BeenThere: bpf@ietf.org X-Mailman-Version: 2.1.39 Precedence: list List-Id: Discussion of BPF/eBPF standardization efforts within the IETF List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 26 Jan 2024 22:27:20 -0000 Yonghong Song wrote:=20 > On 1/25/24 5:12 PM, dthaler1968@googlemail.com wrote: > > The spec defines: > >> As discussed below in `64-bit immediate instructions`_, a 64-bit > >> immediate instruction uses a 64-bit immediate value that is = constructed as > follows. > >> The 64 bits following the basic instruction contain a pseudo > >> instruction using the same format but with opcode, dst_reg, = src_reg, > >> and offset all set to zero, and imm containing the high 32 bits of = the > immediate value. > > [...] > >> imm64 =3D (next_imm << 32) | imm > > The 64-bit immediate instructions section then says: > >> Instructions with the ``BPF_IMM`` 'mode' modifier use the wide > >> instruction encoding defined in `Instruction encoding`_, and use = the > >> 'src' field of the basic instruction to hold an opcode subtype. > > Some instructions then nicely state how to use the full 64 bit > > immediate value, such as > >> BPF_IMM | BPF_DW | BPF_LD 0x18 0x0 dst =3D imm64 > integer integer > >> BPF_IMM | BPF_DW | BPF_LD 0x18 0x2 dst =3D = map_val(map_by_fd(imm)) > + next_imm map fd data pointer > >> BPF_IMM | BPF_DW | BPF_LD 0x18 0x6 dst =3D = map_val(map_by_idx(imm)) > + next_imm map index data pointer > > Others don't: > >> BPF_IMM | BPF_DW | BPF_LD 0x18 0x1 dst =3D map_by_fd(imm) > map fd map > >> BPF_IMM | BPF_DW | BPF_LD 0x18 0x3 dst =3D var_addr(imm) > variable id data pointer > >> BPF_IMM | BPF_DW | BPF_LD 0x18 0x4 dst =3D code_addr(imm) > integer code pointer > >> BPF_IMM | BPF_DW | BPF_LD 0x18 0x5 dst =3D map_by_idx(imm) > map index map > > How is next_imm used in those four? Must it be 0? Or can it be = anything and > it's ignored? > > Or is it used for something? >=20 > The other four must have next_imm to be 0. No use of next_imm in thee = four > insns kindly implies this. > See uapi bpf.h for details (search BPF_PSEUDO_MAP_FD). Thanks for confirming. The "Instruction encoding" section has = misleading text in my opinion. It nicely says: > Note that most instructions do not use all of the fields. Unused = fields shall be cleared to zero. But then goes on to say: > As discussed below in 64-bit immediate instructions (Section 4.4), a = 64-bit immediate instruction > uses a 64-bit immediate value that is constructed as follows. [...] > imm64 =3D (next_imm << 32) | imm Under a normal English reading, that could imply that all 64-bit = immediate instructions use imm64, which is not the case. The whole imm64 discussion there only applies = today to src=3D0 (though I suppose it could be used by future 64-bit immediate instructions). = Minimally I think "a 64-bit immediate instruction uses" should be "some 64-bit immediate = instructions use" but at present there's only one. It would actually be simpler to remove the imm64 text and just have the definition of src 0x0 change from: "dst =3D imm64" to "dst =3D (next_imm = << 32) | imm". What do you think? Dave