From patchwork Mon Jan 25 13:06:25 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Giuliano Procida X-Patchwork-Id: 12045497 X-Patchwork-Delegate: bpf@iogearbox.net 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=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 8DF56C433E0 for ; Tue, 26 Jan 2021 05:37:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5992E2223D for ; Tue, 26 Jan 2021 05:37:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388010AbhAZFhY (ORCPT ); Tue, 26 Jan 2021 00:37:24 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55786 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728622AbhAYNJ2 (ORCPT ); Mon, 25 Jan 2021 08:09:28 -0500 Received: from mail-wr1-x44a.google.com (mail-wr1-x44a.google.com [IPv6:2a00:1450:4864:20::44a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 67343C061794 for ; Mon, 25 Jan 2021 05:06:45 -0800 (PST) Received: by mail-wr1-x44a.google.com with SMTP id u3so7966656wri.19 for ; Mon, 25 Jan 2021 05:06:45 -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=dHCmE0oVXoubM3rTHyQSPX2MJEXLHemPJUmiQIz1gjE=; b=SFOnqGDYvQ3UMYg+Xxq0/jYMkh+nolREupxeeXaZMo7t5sbzBXzhvyD5ZZrXjZHi56 6yyQt6i+aptZKrd6GbcvAUOhf1M5c5fHGYt0F3jPjGCwknFrb8GBxUbScLTCXjZ/Kjsh MG1RbRLYNJ/p1+xjcOOLWENFojsvHpETaL8oUJjGPqL8bz6mNHsJxnZFKh73VkenHEI+ h0y5yuf8DTlo2A0ODTBssz1IVUjCPI+B/3N0ZbzHwaeDfCfsm0fM2JW1lnZ28ih3JZx2 Ouyq8rBiyKRIr8wv8RIdeICRhz6gxKtkiQgM3aJ9A/RctlU2CNK1yyVVBjL91Mefzs41 RZoA== 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=dHCmE0oVXoubM3rTHyQSPX2MJEXLHemPJUmiQIz1gjE=; b=izReoPnpNUzfjxUKlXTtQJkhVoAIyznFZQ2UttrsnCiUQHYcCjpjfSlFFdAKiapUql GaJSs+7hmD6hsy1bDw/EIHJ2dQCkU0jOcQy1o9MKccnm7qLkEJzUi3+D4hkH2FZWEpSo Spj0RoXJjhOW/7gBVnbYi8ITNDJypdzEanaDJuAMMbRyLsV+QEBE8UJolSBrl0UH4jSy 42H+19QhonG5W+cgdrWGjUeMGXkxw9duOo6g1J9PSALOfbgW+ua2Tkvbi1H1tz14H2M9 a2wqOAZGggCG7Shh2fsH4mno7oLd6tPdY/ofyJYCkYozo1vgm14WcVxAwj8XuLhMIzMv nHqw== X-Gm-Message-State: AOAM5328cjBVBfiIhTxh+W+CwsqSg6xi+osZlN2kURVzfgcy/CoZZkfS 8VaDjf9pmcX/JA4UbigJl6h6fOzZjt+8hA== X-Google-Smtp-Source: ABdhPJwLbiQP/xW54xaHyoWge2cRYZKMzVdicac9X6ZmG5acd/9J8zAyuqNenerL/j1SSHfRzykZLtvkQw3dOA== Sender: "gprocida via sendgmr" X-Received: from tef.lon.corp.google.com ([2a00:79e0:d:110:a6ae:11ff:fe11:4f04]) (user=gprocida job=sendgmr) by 2002:a1c:e0d4:: with SMTP id x203mr49589wmg.160.1611580004135; Mon, 25 Jan 2021 05:06:44 -0800 (PST) Date: Mon, 25 Jan 2021 13:06:25 +0000 In-Reply-To: <20210125130625.2030186-1-gprocida@google.com> Message-Id: <20210125130625.2030186-5-gprocida@google.com> Mime-Version: 1.0 References: <20210125130625.2030186-1-gprocida@google.com> X-Mailer: git-send-email 2.30.0.280.ga3ce27912f-goog Subject: [PATCH dwarves 4/4] btf_encoder: Align .BTF section to 8 bytes From: Giuliano Procida To: dwarves@vger.kernel.org Cc: acme@kernel.org, andrii@kernel.org, ast@kernel.org, gprocida@google.com, maennich@google.com, kernel-team@android.com, kernel-team@fb.com, bpf@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org This is to avoid misaligned access to BTF type structs when memory-mapping ELF sections. Signed-off-by: Giuliano Procida --- libbtf.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/libbtf.c b/libbtf.c index 4726e16..fa00053 100644 --- a/libbtf.c +++ b/libbtf.c @@ -755,7 +755,13 @@ static int btf_elf__write(const char *filename, struct btf *btf) * This actually happens in practice with vmlinux which has .strtab * after .shstrtab, resulting in a (small) hole the size of the original * .shstrtab. + * + * We'll align .BTF to 8 bytes to cater for all architectures. It'd be + * nice if we could fetch this value from somewhere. The BTF + * specification does not discuss alignment and its trailing string + * table is not currently padded to any particular alignment. */ + const size_t btf_alignment = 8; /* * First we look if there was already a .BTF section present and @@ -848,8 +854,8 @@ static int btf_elf__write(const char *filename, struct btf *btf) elf_flagdata(btf_data, ELF_C_SET, ELF_F_DIRTY); /* Update .BTF section in the SHT */ - size_t new_btf_offset = high_water_mark; - size_t new_btf_size = raw_btf_size; + size_t new_btf_offset = roundup(high_water_mark, btf_alignment); + size_t new_btf_size = roundup(raw_btf_size, btf_alignment); GElf_Shdr btf_shdr_mem; GElf_Shdr *btf_shdr = gelf_getshdr(btf_scn, &btf_shdr_mem); if (!btf_shdr) { @@ -857,6 +863,7 @@ static int btf_elf__write(const char *filename, struct btf *btf) __func__, elf_errmsg(elf_errno())); goto out; } + btf_shdr->sh_addralign = btf_alignment; btf_shdr->sh_entsize = 0; btf_shdr->sh_flags = 0; if (dot_btf_offset)