From patchwork Sat Jan 27 19:46:29 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yonghong Song X-Patchwork-Id: 13534244 X-Patchwork-Delegate: bpf@iogearbox.net Received: from 69-171-232-180.mail-mxout.facebook.com (69-171-232-180.mail-mxout.facebook.com [69.171.232.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 272D42E84A for ; Sat, 27 Jan 2024 19:46:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=69.171.232.180 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706384810; cv=none; b=ih4jg8DhHf5yYDqEWkeFUbZCYfaz7iB17yEqvbF/vxtCFDqBWWkh+rOW5Y2jIaOvheY0OERAE0QhifuR1gbKeAEmK1ozgnvbKR7V0qkERaPjPb5tNiPw8p41lUkM+D1yTVb6q1pt1+vKLQt2a7yvS2Yg0LzyNhMlJ7RfymOMw4c= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706384810; c=relaxed/simple; bh=Myr63vHqksdUX8vK5MY3FEqunPYeVXDovo7O7hDxvqg=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=lgnXdFvYMpSgVnO/sIOv9RWAO8Bsx6Yas+p3ivj8Ny1huIYq80CGmayUe5B7ueSUa8riLH0kAXBjuAGtCM1UcOA5UWUv2LeEapu1d/MEIB/5bdMMFuBF4o12aNrG8FkN+yQrweWxEM4cReE5BtNK6C0DtFLomAo6uyOhi54BWlI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=fail smtp.mailfrom=linux.dev; arc=none smtp.client-ip=69.171.232.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=linux.dev Received: by devbig309.ftw3.facebook.com (Postfix, from userid 128203) id 7E53C2D182784; Sat, 27 Jan 2024 11:46:29 -0800 (PST) From: Yonghong Song To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , kernel-team@fb.com, Martin KaFai Lau , Dave Thaler Subject: [PATCH bpf-next] [docs/bpf] Improve documentation of 64-bit immediate instructions Date: Sat, 27 Jan 2024 11:46:29 -0800 Message-Id: <20240127194629.737589-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net For 64-bit immediate instruction, 'BPF_IMM | BPF_DW | BPF_LD' and src_reg=[0-6], the current documentation describes the 64-bit immediate is constructed by imm64 = (next_imm << 32) | imm But actually imm64 is only used when src_reg=0. For all other variants (src_reg != 0), 'imm' and 'next_imm' have separate special encoding requirement and imm64 cannot be easily used to describe instruction semantics. This patch clarifies that 64-bit immediate instructions use two 32-bit immediate values instead of a 64-bit immediate value, so later describing individual 64-bit immediate instructions becomes less confusing. Acked-by: Dave Thaler Signed-off-by: Yonghong Song --- .../bpf/standardization/instruction-set.rst | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-) diff --git a/Documentation/bpf/standardization/instruction-set.rst b/Documentation/bpf/standardization/instruction-set.rst index af43227b6ee4..fceacca46299 100644 --- a/Documentation/bpf/standardization/instruction-set.rst +++ b/Documentation/bpf/standardization/instruction-set.rst @@ -166,7 +166,7 @@ Note that most instructions do not use all of the fields. Unused fields shall be cleared to zero. As discussed below in `64-bit immediate instructions`_, a 64-bit immediate -instruction uses a 64-bit immediate value that is constructed as follows. +instruction uses two 32-bit immediate values that are 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. @@ -181,13 +181,8 @@ This is depicted in the following figure:: '--------------' pseudo instruction -Thus the 64-bit immediate value is constructed as follows: - - imm64 = (next_imm << 32) | imm - -where 'next_imm' refers to the imm value of the pseudo instruction -following the basic instruction. The unused bytes in the pseudo -instruction are reserved and shall be cleared to zero. +Here, the imm value of the pseudo instruction is called 'next_imm'. The unused +bytes in the pseudo instruction are reserved and shall be cleared to zero. Instruction classes ------------------- @@ -590,7 +585,7 @@ defined further below: ========================= ====== === ========================================= =========== ============== opcode construction opcode src pseudocode imm type dst type ========================= ====== === ========================================= =========== ============== -BPF_IMM | BPF_DW | BPF_LD 0x18 0x0 dst = imm64 integer integer +BPF_IMM | BPF_DW | BPF_LD 0x18 0x0 dst = (next_imm << 32) | imm integer integer BPF_IMM | BPF_DW | BPF_LD 0x18 0x1 dst = map_by_fd(imm) map fd map BPF_IMM | BPF_DW | BPF_LD 0x18 0x2 dst = map_val(map_by_fd(imm)) + next_imm map fd data pointer BPF_IMM | BPF_DW | BPF_LD 0x18 0x3 dst = var_addr(imm) variable id data pointer