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=-7.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS autolearn=no 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 9C4EFC433B4 for ; Mon, 3 May 2021 20:20:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 73007611AC for ; Mon, 3 May 2021 20:20:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229497AbhECUVg (ORCPT ); Mon, 3 May 2021 16:21:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44208 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229472AbhECUVg (ORCPT ); Mon, 3 May 2021 16:21:36 -0400 Received: from mail-vs1-xe29.google.com (mail-vs1-xe29.google.com [IPv6:2607:f8b0:4864:20::e29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CE242C06174A for ; Mon, 3 May 2021 13:20:42 -0700 (PDT) Received: by mail-vs1-xe29.google.com with SMTP id o192so3603767vsd.7 for ; Mon, 03 May 2021 13:20:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=qMOwLFmz6GugapCkf5uuvpANHBPJMCc9AvAkHonn0cI=; b=EPyWrLgtgQ5Ac9pBZ4rDSsyGEtWwgI6tTyNPRVrT+e6rilJXLzNmcKGEeHtBgv0vcd FOuii4RFjbLeOsUVsh77gG8AmPal82W9KpZ8k0nLMbAoZauKggL+891xUqIFK6aQALSt eY2oUqPf63XsC4l2PVYZTjLUDbFnW5hbNzxFf3abbrlionp+rfA7NBizBt74eTdHHy70 m0N3rzQ0iyhwQdUL7dToYJcwJDr5o0jLVbMHbEqPEF2qKRkt7VCIrkeBBLVssMPLOxpb jhqzvZMhbTvr0hcaa2j+M7LOBkrLOrM/qvt6EeUKWOZzKLbajMsigMw/50HSDn3zjAds ZrZQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=qMOwLFmz6GugapCkf5uuvpANHBPJMCc9AvAkHonn0cI=; b=rhWH+5J3LaRE8LcqDDD0ghZjOgRVtxH6pXpdLTetPhgRDk+dWPbVK/AL4EaFj7eBbC wjrfKR5jtWkqsdumivHTdxfKc6M5piLSwZvkokeCweHGjRYFxLjEskCDq1FtHtgnKrNG oZIjieBJdj3VB1NGQtVd8tMrw0DN9rXPkV6IgRdXG5eQSZ26nukqWDhoOmGkY7faVjWG jldrd2bzTdblBpighuKc8dGgg8K+PnVHZY1+MdhwqwFh6tZY8uSfEzIgAHY+rXpsKXkR h+8MDbrKaW/PJHz/vBX7irZySWrYrAywMz0fHBulR097gF7Cvwv8V9FdG2g4UIvxCNfZ FMQw== X-Gm-Message-State: AOAM5314w9ENNZDGsy1WdW/SO5jFykPDNwsxf+MCpSZop37sEymaDAmd bm/xWSHsNl4jJiqUqCHncdVO/+96fpYeoV9q9QM= X-Google-Smtp-Source: ABdhPJwySJgTSEPWJbAV2OIo7bhWgyXetlNblSTZMYM2NtZvvph+hfcLpGksz8aCP7Kx6Pitst4Ygq7yIYgikpMcNxU= X-Received: by 2002:a05:6102:507:: with SMTP id l7mr4227499vsa.25.1620073241795; Mon, 03 May 2021 13:20:41 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Grant Seltzer Richman Date: Mon, 3 May 2021 16:20:30 -0400 Message-ID: Subject: Re: Typical way to handle missing macros in vmlinux.h To: Andrii Nakryiko Cc: bpf Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, May 3, 2021 at 2:43 PM Andrii Nakryiko wrote: > > On Mon, May 3, 2021 at 11:32 AM Grant Seltzer Richman > wrote: > > > > On Wed, Apr 28, 2021 at 5:15 PM Andrii Nakryiko > > wrote: > > > > > > On Wed, Apr 28, 2021 at 1:53 PM Grant Seltzer Richman > > > wrote: > > > > > > > > Hi all, > > > > > > > > I'm working on enabling CO:RE in a project I work on, tracee, and am > > > > running into the dilemma of missing macros that we previously were > > > > able to import from their various header files. I understand that > > > > macros don't make their way into BTF and therefore the generated > > > > vmlinux.h won't have them. However I can't import the various header > > > > files because of multiple-definition issues. > > > > > > Sadly, copy/pasting has been the only way so far. > > > > > > > > > > > Do people typically redefine each of these macros for their project? > > > > If so is there anything I should be careful of, such as architectural > > > > differences. Does anyone have creative ideas, even if not developed > > > > fully yet that I can possibly contribute to libbpf? > > > > > > We've discussed adding Clang built-in to detect if a specific type is > > > already defined and doing something like this in vmlinux.h: > > > > > > #if !__builtin_is_type_defined(struct task_struct) > > > struct task_struct { > > > ... > > > } > > > #endif > > > > > > And just do that for every struct, union, typedef. That would allow > > > vmlinux.h to co-exist (somewhat) with other types. > > > > > > Another alternative is to not use vmlinux.h and use just linux > > > headers, but mark necessary types with > > > __attribute__((preserve_access_index)) to make them CO-RE relocatable. > > > You can add that to existing types with the same pragma that vmlinux.h > > > uses. > > > > I'm attempting to try doing the above. I'm just replacing > > bpf_probe_read with bpf_core_read and not importing vmlinux.h, just > > all the kernel headers I need. > > Yes, that will work, bpf_core_read() uses preserve_access_index > built-in to achieve the same effect. > > > > > When you say "Add that to existing types with the same pragma that > > vmlinux.h uses", Should I be able to add the following to my bpf > > source file before importing my headers? > > > > ifndef BPF_NO_PRESERVE_ACCESS_INDEX > > #pragma clang attribute push (__attribute__((preserve_access_index)), > > apply_to = record) > > #endif > > > > and then pop the attribute at the bottom of the file, or after the > > header includes. > > Yeah, that's the idea and that's what vmlinux.h does for all its > structs. It doesn't add __attribute__((preserve_access_index)) after > each struct/union. So I wonder why you are getting those unknown > attribute errors. Can you paste an example? Here's a couple examples of the warnings: ``` tracee/tracee.bpf.c:5:46: warning: unknown attribute 'preserve_access_index' ignored [-Wunknown-attributes] #pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record) ^ /lib/modules/5.10.21-200.fc33.x86_64/source/include/linux/ipv6.h:185:1: note: when applied to this declaration struct ipv6_fl_socklist; ^ tracee/tracee.bpf.c:5:46: warning: unknown attribute 'preserve_access_index' ignored [-Wunknown-attributes] #pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record) ^ /lib/modules/5.10.21-200.fc33.x86_64/source/include/linux/ipv6.h:187:1: note: when applied to this declaration struct inet6_cork { ``` after these warnings are emitted (it seems as if there's one for every data type, though I can't confirm), I get errors that look like this: ``` tracee/tracee.bpf.c:445:22: error: nested builtin_preserve_access_index() not supported return READ_KERN(READ_KERN(task->thread_pid)->numbers[level].nr); ^ tracee/tracee.bpf.c:206:27: note: expanded from macro 'READ_KERN' bpf_core_read(&_val, sizeof(_val), &ptr); \ ``` I believe this is just a result of the warnings above, but if you're curious it's what i'm doing here: https://github.com/aquasecurity/tracee/blob/core-experiment/tracee-ebpf/tracee/tracee.bpf.c#L204-L208 > > Also check that you use Clang that supports preserve_access_index, of course. I'm using clang 11.0 on Fedora 33. All dependencies appear properly installed (libelf, zlib, dwarves [provides pahole], llvm, llc, llvm-devel,...) > > > > > I've tried this and get a whole bunch of 'unknown attribute' warnings, > > leading me to believe that I either have something installed > > incorrectly or don't understand how to use clang attributes. Do I need > > to edit the types in the actual header files? > > No, the whole idea is to not touch original headers. Got it - that's good to know. > > > > > Thank you very very much for the help! > > - Grant > > > > > > > > > > > Thanks so much, > > > > Grant Seltzer