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=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 0562CC433E0 for ; Thu, 18 Mar 2021 19:47:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A59DC64F1D for ; Thu, 18 Mar 2021 19:47:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229958AbhCRTqh (ORCPT ); Thu, 18 Mar 2021 15:46:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39330 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232935AbhCRTqO (ORCPT ); Thu, 18 Mar 2021 15:46:14 -0400 Received: from mail-yb1-xb2f.google.com (mail-yb1-xb2f.google.com [IPv6:2607:f8b0:4864:20::b2f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BCA27C06174A for ; Thu, 18 Mar 2021 12:46:13 -0700 (PDT) Received: by mail-yb1-xb2f.google.com with SMTP id o83so3839133ybg.1 for ; Thu, 18 Mar 2021 12:46:13 -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=b2NnDAMdril70A+p9ccUB8pp0KGuaUAQFd+hCpCLTDQ=; b=nAPHFn3niprsveMBw2utSHiAn5+eJm1jB0iF/FZhTL2P9wfapE1IP5Gd7p742u82id Y5Fp5cSkB3KD/PCtXHWnr7UBaTkdL3fAfHLM/ko77lT5aj0NwUeb6R+2JKTbrA5Mwta9 GZLB/h+BEy00ZRo39UocnCeC8lWJ0eOaUMcojJhiLnXQ8tzDtHEYZuWW35qJQZTPzwwY MNrzBB9ccI0vgz8vj2bJvInhGdASw0KAHIGWcrqRLyormYbh6AudLhkXpbLxoo+OErpY xpPV1kzA6GAwD5OvFULhu6JrW2p3IOYo2g1vgZH/9e823E8Bqkb6b5juMfeBAjsiVzqW nebw== 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=b2NnDAMdril70A+p9ccUB8pp0KGuaUAQFd+hCpCLTDQ=; b=MIGwiS/0CzpDeY59Cju38MbEN4oaJJ9DFK2IOoVvTy4QZwsLLhghDhoeXY+K8+x5/U 77+usbWiDnKeWZiuAxw+2oSPLMsmsbNGCSYVPVggN1OGdYGR1sfSB1RD5aWlZrpFwJsu v/rEhbtZvfmi6zT9VxqVco//Rv0B+aIp3qkrnawaZ66BjkId81ZUeGb5SgtbBIzTyrKC cJ3pqLBi2LOMBNhLfWOh/jl8DYqC70Aooy4gzyGqe2cCWjfo1GVJv1pjIVof27QP4+1R zFzl/G+ygxLbTvddtQnTa/Xejy8c+jFgOwz3C/KZD+ltgFDL9RrVdlqzDk1kOVoyDTnw Kkvw== X-Gm-Message-State: AOAM530bBs2UpblRwQYi0mQDCyEhgm5Yfqvr5WWRrFHFVlWRfzpZEyMy 8unAwHLok5gFRGuy8JR9DOQahJcs9DxRd+0eWf+o+6hadaD+Pw== X-Google-Smtp-Source: ABdhPJzbniwlpedVTx6R7cONOZF2NfZgEuf3Fice25e1GiU/5CxDs0GUkMUZ/XJIxYEQKTWpUIyeI5A7W22Vx/g0BkY= X-Received: by 2002:a25:40d8:: with SMTP id n207mr1319430yba.459.1616096772978; Thu, 18 Mar 2021 12:46:12 -0700 (PDT) MIME-Version: 1.0 References: <20210318062520.3838605-1-rafaeldtinoco@ubuntu.com> <20210318193121.370561-1-rafaeldtinoco@ubuntu.com> In-Reply-To: <20210318193121.370561-1-rafaeldtinoco@ubuntu.com> From: Andrii Nakryiko Date: Thu, 18 Mar 2021 12:46:02 -0700 Message-ID: Subject: Re: [PATCH] libbpf: allow bpf object kern_version to be overridden To: Rafael David Tinoco Cc: bpf Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Thu, Mar 18, 2021 at 12:31 PM Rafael David Tinoco wrote: > > Unfortunately some distros don't have their accurate kernel version > defined correctly in version.h due to long term support decisions. This > makes LINUX_VERSION_CODE to be defined as the original upstream version > in header, while the running in-kernel version is different. > > Older kernels might still check kern_version during bpf_prog_load(), > making it impossible to load a program that could still be portable. > This patch allows one to override bpf objects kern_version attributes, > so program can bypass this in-kernel check during load. > > Example: > > A kernel 4.15.0-129.132, for example, might have 4.15.18 version defined > in its headers, which is the kernel it is based on, but have a 4.15.0 > version defined within the kernel due to other factors. > > $ export LIBBPF_KERN_VERSION=4.15.18 > $ sudo -E ./portablebpf -v > ... > libbpf: bpf object: kernel_version enforced by env variable: 266002 > ... > > This will also help portable binaries within similar older kernels, as > long as they have their BTF data converted from DWARVES (for example). > > Signed-off-by: Rafael David Tinoco > --- Libbpf currently provides a way to specify custom kernel version using a special "version" ELF section: int _version SEC("version") = 123; But it seems like you would want to set it at runtime, so this compile-time approach might be problematic. But instead of hijacking get_kernel_version(), it's better to add a simple setter counterpart to bpf_object__kversion() that would just override obj->kern_version. > src/libbpf.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/src/libbpf.c b/src/libbpf.c > index 4dc09d3..cbc6e61 100644 > --- a/src/libbpf.c > +++ b/src/libbpf.c > @@ -708,13 +708,19 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data, > > static __u32 get_kernel_version(void) > { > - __u32 major, minor, patch; > struct utsname info; > + __u32 major, minor, patch, ver; > + char *ptr, *e = getenv("LIBBPF_KERN_VERSION"); > > uname(&info); > - if (sscanf(info.release, "%u.%u.%u", &major, &minor, &patch) != 3) > + ptr = (e != NULL) ? e : (char *) &info.release; > + if (sscanf(ptr, "%u.%u.%u", &major, &minor, &patch) != 3) > return 0; > - return KERNEL_VERSION(major, minor, patch); > + ver = KERNEL_VERSION(major, minor, patch); > + if (e) > + pr_debug("bpf object: kernel_version enforced by env variable: %u\n", ver); > + > + return ver; > } > > static const struct btf_member * > -- > 2.17.1 >