From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4AAF8C433DB for ; Mon, 18 Jan 2021 16:01:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 15FC022B49 for ; Mon, 18 Jan 2021 16:01:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404676AbhARQAo (ORCPT ); Mon, 18 Jan 2021 11:00:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45366 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390669AbhARQAk (ORCPT ); Mon, 18 Jan 2021 11:00:40 -0500 Received: from mail-wm1-x34a.google.com (mail-wm1-x34a.google.com [IPv6:2a00:1450:4864:20::34a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA0EFC061786 for ; Mon, 18 Jan 2021 07:59:11 -0800 (PST) Received: by mail-wm1-x34a.google.com with SMTP id r1so4702953wmn.8 for ; Mon, 18 Jan 2021 07:59:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:in-reply-to:message-id:mime-version:references:subject :from:to:cc; bh=6OdTPYEA2p5+e67drhVq+n88z8c6ioQj4MZmywIDAFM=; b=eMBuLjmixjlbs4KF0qZwuBWsre4MhQNj8gm7XxkbXIPimS+tmeY3wm5Tke/4fDyObv J7FhRpPLOUyZ0NkB7PA9Whh3FFh/p4zRylDnczG+AOHircxNJd35i3cmWageo/SngS6F +pW8+PP117T9sFvwjbYfoOL06tsyW6srmnXTBEbbhcpDTG7Hvn0dpBpV39Jx35cmxWr2 /qLfWcOFJHeCP6JN6sMRxyEmS4zkokORJhKHdr/XW8BoHiv8rm7yiZ0+2V6ABjqFxyNz r9Z6s0Lbx39CdrnhmIkAPnCj/h3bH+OuVy3XNiwSKHvJtIqR/06iUUW9y7ilPymgagbD 8g2g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=6OdTPYEA2p5+e67drhVq+n88z8c6ioQj4MZmywIDAFM=; b=ZjPPqtwKC2A8zYpwtjtiKKqN9LX1DaGG3kADoSbRO8PYiNUW+7v2kyX88ND18bbfwU MFOt7tr8wY2lcITG2qLzZK7aD7X7USAN651OyBAQYp5Bf+Z+nM0O5qDd/MOLouipPM/V Cq9ua2BOzeusxdO9LZaSxXUSulQ+Qxyl/lHPnghocRlZSF/M/BUaezXNc4XX3iyrQDz6 rN2OCFu/sZJMctl3l2jejvHAa9MhNeiaHmqIv2EdOOqQOxNLduPGi4cWb83vwz39bg5W qqQJnHJZ99jKglBqTiFlLK+jWxAc7IJfaSwiLhfBPig65tydaF+sZloFr3l/R+TZnlcv /VnA== X-Gm-Message-State: AOAM5331cPjE0sDp06BZP5YbUO0PD0Tij9pX8i1qtwIvfj8GNPt58DDu emTzhTOneLJw8axtQgW7O/jZvt2olXFRWTZCwMR3TaUiwGgF6Gm2bO6ZAn28gShFJxzushrQTCZ DlpjdPZlqMS50MTPWDVU4IdVR/9onbgZgdEw77VVCtMDTBewVY2OKAERSwz850N8= X-Google-Smtp-Source: ABdhPJx33zg0bqJm2Kmy1Jtk2wZJhRlq1DTndo3IekH3vxXdp0oYMj9T3RZMul5MMDMPA5R/Y/vw0BsdArAwKg== Sender: "jackmanb via sendgmr" X-Received: from beeg.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:11db]) (user=jackmanb job=sendgmr) by 2002:a1c:6208:: with SMTP id w8mr82357wmb.24.1610985550410; Mon, 18 Jan 2021 07:59:10 -0800 (PST) Date: Mon, 18 Jan 2021 15:57:35 +0000 In-Reply-To: <20210118155735.532663-1-jackmanb@google.com> Message-Id: <20210118155735.532663-3-jackmanb@google.com> Mime-Version: 1.0 References: <20210118155735.532663-1-jackmanb@google.com> X-Mailer: git-send-email 2.30.0.284.gd98b1dd5eaa7-goog Subject: [PATCH bpf-next v2 2/2] docs: bpf: Clarify -mcpu=v3 requirement for atomic ops From: Brendan Jackman To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , KP Singh , Florent Revest , Lukas Bulwahn , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Jonathan Corbet , Brendan Jackman Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Alexei pointed out [1] that this wording is pretty confusing. Here's an attempt to be more explicit and clear. [1] https://lore.kernel.org/bpf/CAADnVQJVvwoZsE1K+6qRxzF7+6CvZNzygnoBW9tZNWJELk5c=Q@mail.gmail.com/T/#m07264fc18fdc43af02fc1320968afefcc73d96f4 Signed-off-by: Brendan Jackman --- Documentation/networking/filter.rst | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst index 4c2bb4c6364d..b3f457802836 100644 --- a/Documentation/networking/filter.rst +++ b/Documentation/networking/filter.rst @@ -1081,9 +1081,10 @@ before is loaded back to ``R0``. Note that 1 and 2 byte atomic operations are not supported. -Except ``BPF_ADD`` *without* ``BPF_FETCH`` (for legacy reasons), all 4 byte -atomic operations require alu32 mode. Clang enables this mode by default in -architecture v3 (``-mcpu=v3``). For older versions it can be enabled with +Clang can generate atomic instructions by default when ``-mcpu=v3`` is +enabled. If a lower version for ``-mcpu`` is set, the only atomic instruction +Clang can generate is ``BPF_ADD`` *without* ``BPF_FETCH``. If you need to enable +the atomics features, while keeping a lower ``-mcpu`` version, you can use ``-Xclang -target-feature -Xclang +alu32``. You may encounter ``BPF_XADD`` - this is a legacy name for ``BPF_ATOMIC``, -- 2.30.0.284.gd98b1dd5eaa7-goog