From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9148835975; Mon, 9 Dec 2024 15:20:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733757621; cv=none; b=a6r777glFq/TmppsYHkHyUZnwtyQooMtHMyJkIK2TK0FDgaGtFEg4xpArr/2MICWtsTPK+n5ymCGGSEcqU1X0ij8RBgJwUXpv4sGvM71Y+RPOM9e501sYdsNFksg35itwBqHckC842V9qBEuoWLTLk1ei9D7T6HmOKh9DMY12FE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733757621; c=relaxed/simple; bh=YZveUo7ygVztpPq12Big4of4v0JPqpekSILGg/8Xioo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lv8FuZxj+pd9UPKeTV75RjSfiQWO9l+u5HUN3vO2hTE0qb4XpubaTDU8NkHbsutoTT5WkjnQt1nlyFp4vIolZxylIiiV+kg1kZssSz0eGsV/EJdzZbxFGTSl+WtUAZkQY1MGjTViE70uyk0DzCJZqUtE0vCCsUMTAUGI6TKz9Eo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WjGxYIgn; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WjGxYIgn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A44A0C4CED1; Mon, 9 Dec 2024 15:20:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1733757621; bh=YZveUo7ygVztpPq12Big4of4v0JPqpekSILGg/8Xioo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=WjGxYIgnZSRGPsPcxvScWnB5MN3VxGQVxaKuzqqqJwkzqnE104gQRAch/4hmvfXGD +hq00abe6HezBdxcnl43mbYNKsokvDKRZLlgk5uSjvllF/3R7OFEx0UDuK0zywVNyP d1VQrwY2QYP4KxmMIEVYzRrBJ8R2O3HSnUG+AHZtUWMV/c61ki4rRACpGqGguQFJpc 1UzSoQ5JXBfnisrifZCLw2UX9SVijhELSwcHpUmpjzdJNma1Xu46eYvMtl4C9BDbTb HQKZrvJ+7xGCK9JsrBGrQQKzBJaIy/KGR+XS3ddi+phE+IwlX9FYUYT+006uzUCI5o vD/srrIUqLH6A== Message-ID: <11d588c2-febe-46c4-ab49-8fb0ed80faac@kernel.org> Date: Mon, 9 Dec 2024 15:20:15 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v2] bpftool: Probe for ISA v4 instruction set extension To: Simone Magnani , bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, nathan@kernel.org, ndesaulniers@google.com, morbo@google.com, justinstitt@google.com, linux-kernel@vger.kernel.org, llvm@lists.linux.dev References: <20241209102644.29880-1-simone.magnani@isovalent.com> <20241209145439.336362-1-simone.magnani@isovalent.com> From: Quentin Monnet Content-Language: en-GB In-Reply-To: <20241209145439.336362-1-simone.magnani@isovalent.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 09/12/2024 14:54, Simone Magnani wrote: > This patch introduces a new probe to check whether the kernel supports > instruction set extensions v4. The v4 extension comprises several new > instructions: BPF_{SDIV,SMOD} (signed div and mod), BPF_{LD,LDX,ST,STX,MOV} > (sign-extended load/store/move), 32-bit BPF_JA (unconditional jump), > target-independent BPF_ALU64 BSWAP (byte-swapping 16/32/64). These have > been introduced in the following commits respectively: > > * ec0e2da ("bpf: Support new signed div/mod instructions.") > * 1f9a1ea ("bpf: Support new sign-extension load insns") > * 8100928 ("bpf: Support new sign-extension mov insns") > * 4cd58e9 ("bpf: Support new 32bit offset jmp instruction") > * 0845c3d ("bpf: Support new unconditional bswap instruction") > > Support in bpftool for previous ISA extensions were added in commit > 0fd800b2 ("bpftool: Probe for instruction set extensions"). These probes > are useful for userspace BPF projects that want to use newer > instruction set extensions on newer kernels, to reduce the programs' > sizes or their complexity. LLVM provides the mcpu=v4 option since commit > "[BPF] support for BPF_ST instruction in codegen" > (https://github.com/llvm/llvm-project/commit/8f28e8069c4ba1110daee8bddc4d5049b6d4646e). > > Changelog: > > - v2: > - moved BPF_JMP32_A macro after BPF_JMP_A in filter.h for consistency > with include/linux/filter.h, noted by Quentin Monnet > > Signed-off-by: Simone Magnani > --- > tools/bpf/bpftool/feature.c | 23 +++++++++++++++++++++++ > tools/include/linux/filter.h | 10 ++++++++++ > 2 files changed, 33 insertions(+) > > diff --git a/tools/bpf/bpftool/feature.c b/tools/bpf/bpftool/feature.c > index 4dbc4fcdf473..24fecdf8e430 100644 > --- a/tools/bpf/bpftool/feature.c > +++ b/tools/bpf/bpftool/feature.c > @@ -885,6 +885,28 @@ probe_v3_isa_extension(const char *define_prefix, __u32 ifindex) > "V3_ISA_EXTENSION"); > } > > +/* > + * Probe for the v4 instruction set extension introduced in commit 1f9a1ea821ff > + * ("bpf: Support new sign-extension load insns"). > + */ > +static void > +probe_v4_isa_extension(const char *define_prefix, __u32 ifindex) > +{ > + struct bpf_insn insns[5] = { > + BPF_MOV64_IMM(BPF_REG_0, 0), > + BPF_JMP32_IMM(BPF_JEQ, BPF_REG_0, 1, 1), Looking again at the probe itself, does the second instruction serve any practical purpose here? Don't you just need to test the BPF_JMP32_A? Looks good otherwise, thank you! Reviewed-by: Quentin Monnet > + BPF_JMP32_A(1), > + BPF_MOV64_IMM(BPF_REG_0, 1), > + BPF_EXIT_INSN() > + };