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=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 59815C43331 for ; Fri, 27 Mar 2020 12:24:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C3BE2082D for ; Fri, 27 Mar 2020 12:24:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MCc2tYnJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726540AbgC0MYp (ORCPT ); Fri, 27 Mar 2020 08:24:45 -0400 Received: from us-smtp-delivery-74.mimecast.com ([63.128.21.74]:39753 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726454AbgC0MYp (ORCPT ); Fri, 27 Mar 2020 08:24:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585311884; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=vosgrYq+dIB9YWWJ2hoVCefw2rREFv5Y6PKVFxbbPF8=; b=MCc2tYnJs/Dy9yXWqjHZ2mzVaO9q067n/SPxnlqXy1AkzadFfYkd7lPbnM8+26+kcMj81b Ile+KdGZZf9uodfkVPWRkA9gY+hnyGMz+1vdxTfGvCf21iwpGlzzJtlpwmkT4zh+8uRJxQ XRK04glxZY8k2TyhnamO3Ij4IwD9bA0= Received: from mail-lf1-f69.google.com (mail-lf1-f69.google.com [209.85.167.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-36-dNZBMZ3WM7uHCYCxL_1APw-1; Fri, 27 Mar 2020 08:24:42 -0400 X-MC-Unique: dNZBMZ3WM7uHCYCxL_1APw-1 Received: by mail-lf1-f69.google.com with SMTP id l3so3469251lfe.22 for ; Fri, 27 Mar 2020 05:24:42 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version:content-transfer-encoding; bh=vosgrYq+dIB9YWWJ2hoVCefw2rREFv5Y6PKVFxbbPF8=; b=TxVzm6nYA/DYc0IGsMeZYSFnaf1TMTj69GxslhB0h246S2KzPLmrhioaqrud5ceIL8 Q3n5E5xMeOoWfC11bGws+3heGqMIErksc1wpdZbkzEaCXUNllojhn4aDBPoAe429UWtQ UVEqMBEvjHQvqCUrwEGOOyKpOl+DfAQdqoaKnwJF6p1Z0P3Qwg3yI4YPk7yxIGd4sFv7 RkKl9UV0en+8IQGBaQKFj39jy5dZc5X0iyKWrPbwRo1xn+UBTBzTOTKRkkVB5WkFxYmX CE6fHEidGdDuEhyVUW9JvZ22Yb9d2AQNzXV7vbV57hY+Mrc4Dy8UmWwVE5Uzrr7L83O3 LPnw== X-Gm-Message-State: AGi0PuZEB9nCqKWphhcvzEZLChQ8Gdt28a01blZ4j0lncct8gmjYIFAa qDBh5ym6VQEcYQtYSklEd+rsVDfqiHcM3yA8MLkgBYZ6lYiE5ROMW5E56CfWK8nOBsRHisH6I2U ZEhDeZrEbsG2x X-Received: by 2002:a2e:5ce:: with SMTP id 197mr8443874ljf.234.1585311881194; Fri, 27 Mar 2020 05:24:41 -0700 (PDT) X-Google-Smtp-Source: ADFU+vsawMB3aEM37Jpmcuqewkciu2tzCjDejZAco2JHqvmvthSuGn1Bt2m4GUyqM9mRg3sz6u2W3g== X-Received: by 2002:a2e:5ce:: with SMTP id 197mr8443864ljf.234.1585311880946; Fri, 27 Mar 2020 05:24:40 -0700 (PDT) Received: from alrua-x1.borgediget.toke.dk ([45.145.92.2]) by smtp.gmail.com with ESMTPSA id h6sm2655635lji.39.2020.03.27.05.24.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Mar 2020 05:24:39 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id CF82618158B; Fri, 27 Mar 2020 13:24:37 +0100 (CET) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Andrii Nakryiko Cc: Daniel Borkmann , Alexei Starovoitov , bpf , Networking Subject: Re: [PATCH bpf-next] libbpf: Add bpf_object__rodata getter function In-Reply-To: References: <20200326151741.125427-1-toke@redhat.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Fri, 27 Mar 2020 13:24:37 +0100 Message-ID: <87eetem1dm.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Andrii Nakryiko writes: > On Thu, Mar 26, 2020 at 8:18 AM Toke H=C3=B8iland-J=C3=B8rgensen wrote: >> >> This adds a new getter function to libbpf to get the rodata area of a bpf >> object. This is useful if a program wants to modify the rodata before >> loading the object. Any such modification needs to be done before loadin= g, >> since libbpf freezes the backing map after populating it (to allow the >> kernel to do dead code elimination based on its contents). >> >> Signed-off-by: Toke H=C3=B8iland-J=C3=B8rgensen >> --- >> tools/lib/bpf/libbpf.c | 13 +++++++++++++ >> tools/lib/bpf/libbpf.h | 1 + >> tools/lib/bpf/libbpf.map | 1 + >> 3 files changed, 15 insertions(+) >> >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c >> index 085e41f9b68e..d3e3bbe12f78 100644 >> --- a/tools/lib/bpf/libbpf.c >> +++ b/tools/lib/bpf/libbpf.c >> @@ -1352,6 +1352,19 @@ bpf_object__init_internal_map(struct bpf_object *= obj, enum libbpf_map_type type, >> return 0; >> } >> >> +void *bpf_object__rodata(const struct bpf_object *obj, size_t *size) > > We probably don't want to expose this API. It just doesn't scale, > especially if/when we add support for custom sections names for global > variables. Right. I was not aware of any such plans, but OK. > Also checking for map->mmaped is too restrictive. See how BPF skeleton > solves this problem and still allows .rodata initialization even on > kernels that don't support memory-mapping global variables. Not sure what you mean here? As far as I can tell, the map->mmaped pointer has nothing to do with the kernel support for mmaping the map contents. It's just what libbpf does to store the data of any internal_maps? I mean, bpf_object__open_skeleton() just does this: if (mmaped && (*map)->libbpf_type !=3D LIBBPF_MAP_KCONFIG) *mmaped =3D (*map)->mmaped; which amounts to the same as I'm doing in this patch? > But basically, why can't you use BPF skeleton? Couple of reasons: - I don't need any of the other features of the skeleton - I don't want to depend on bpftool in the build process - I don't want to embed the BPF bytecode into the C object > Also, application can already find that map by looking at name. Yes, it can find the map, but it can't access the data. But I guess I could just add a getter for that. Just figured this was easier to consume; but I can see why it might impose restrictions on future changes, so I'll send a v2 with such a map-level getter instead. -Toke