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=-11.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 D2740C10F29 for ; Tue, 17 Mar 2020 05:09:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9614C20674 for ; Tue, 17 Mar 2020 05:09:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="PPx+NJdH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725785AbgCQFJZ (ORCPT ); Tue, 17 Mar 2020 01:09:25 -0400 Received: from mail-qk1-f194.google.com ([209.85.222.194]:42474 "EHLO mail-qk1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725730AbgCQFJY (ORCPT ); Tue, 17 Mar 2020 01:09:24 -0400 Received: by mail-qk1-f194.google.com with SMTP id e11so30436030qkg.9; Mon, 16 Mar 2020 22:09:23 -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=ioTZr5nsJG3HFizDxsGwRshIWndCqjqQER0RaugL3L8=; b=PPx+NJdHygj257ZbMXduTiKasHi4manKnYEq+k9yf6OGc2GmJuIqIdX5FISUSdeCdn sjvGorhk/PIvmieYYQl8noFyVgnDcELyiv1k+M4VtFb25AQczZckCbsrpdG+s4I+U/FW Lw6nvbJuxdTRCe9R5TecAH4YyKNc2BoBJSfE2FdRMfG0WNpiLA9svpgEQfQz26+arisd Q9aZcU5AnZqOoujjR/PQYQNLmIcGCY/PXwZZrnfUxmasur09grnjMiHBd4nW9cQOZkyB 1W9vgI4LmWhQuHTSQNsYoZhzgkaDtIWyps3Vmqj7VL5nZluRH0uaPOIWIHURfZIf3pgV GXhA== 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=ioTZr5nsJG3HFizDxsGwRshIWndCqjqQER0RaugL3L8=; b=HOsOGhzYayxKAM7mm3UbkA6+n8wNdO8AUCQqTwW10Bw9o32AxBgVLdrNH8wNmjCpqa 8282dHO0mj2J8Z6WUl3UdxqpW/Wew8x0epeWB+AVrc5rr4mraXA+mQOtrGRlsQIUPnII ZgJfvz7GpFINpwU1wNer+IRou2Ndojq8PVMwj+OTvbAfsCWeJIYVS/nayr4lRBT23/HQ CoPXC4GFdTxJsEmD5tdkYLkDiamN8+KvucoXGIpUoSPYrmQqNTgT+KkAN8zxdvm+SAJQ NPX+8ZeUOJWI5pxA2zegWU4vOeGFcWyW/KW0uZwNXcDaUfbGqI3XbCBQEGQe9xLSeFdb 0X4g== X-Gm-Message-State: ANhLgQ3YySXoyTxAFC60o6642oOlXudtJHZaAYkWEBGn2TUkwk5DxlHb cBNX31BGwIz766cKD1prjexKpaR+RiKv59q8MRU= X-Google-Smtp-Source: ADFU+vsObjY46cgRCG0SveVJO26y2xkuT75EZ4lIZG+1Z/6zXEYZwdC6cE17to6SmQFoNAMxiEO1P79dYYsbTyHXVCs= X-Received: by 2002:a37:9104:: with SMTP id t4mr3307894qkd.449.1584421763202; Mon, 16 Mar 2020 22:09:23 -0700 (PDT) MIME-Version: 1.0 References: <20200317011654.zkx5r7so53skowlc@google.com> <20200317033701.w7jwos7mvfnde2t2@google.com> In-Reply-To: <20200317033701.w7jwos7mvfnde2t2@google.com> From: Andrii Nakryiko Date: Mon, 16 Mar 2020 22:09:12 -0700 Message-ID: Subject: Re: [PATCH bpf v2] bpf: Support llvm-objcopy and llvm-objdump for vmlinux BTF To: Fangrui Song Cc: bpf , Networking , Daniel Borkmann , Nick Desaulniers , Nathan Chancellor , clang-built-linux@googlegroups.com, Stanislav Fomichev , "David S. Miller" , Alexei Starovoitov Content-Type: text/plain; charset="UTF-8" Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, Mar 16, 2020 at 8:37 PM Fangrui Song wrote: > > On 2020-03-16, Andrii Nakryiko wrote: > >On Mon, Mar 16, 2020 at 6:17 PM Fangrui Song wrote: > >> > >> Simplify gen_btf logic to make it work with llvm-objcopy and > >> llvm-objdump. We just need to retain one section .BTF. To do so, we can > >> use a simple objcopy --only-section=.BTF instead of jumping all the > >> hoops via an architecture-less binary file. > >> > >> We use a dd comment to change the e_type field in the ELF header from > >> ET_EXEC to ET_REL so that .btf.vmlinux.bin.o will be accepted by lld. > >> > >> Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux") > >> Cc: Stanislav Fomichev > >> Cc: Nick Desaulniers > >> Tested-by: Nick Desaulniers > >> Reported-by: Nathan Chancellor > >> Link: https://github.com/ClangBuiltLinux/linux/issues/871 > >> Signed-off-by: Fangrui Song > >> --- > >> scripts/link-vmlinux.sh | 13 ++----------- > >> 1 file changed, 2 insertions(+), 11 deletions(-) > >> > >> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > >> index dd484e92752e..84be8d7c361d 100755 > >> --- a/scripts/link-vmlinux.sh > >> +++ b/scripts/link-vmlinux.sh > >> @@ -120,18 +120,9 @@ gen_btf() > >> > >> info "BTF" ${2} > >> vmlinux_link ${1} > >> - LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} > > > >Is it really tested? Seems like you just dropped .BTF generation step > >completely... > > Sorry, dropped the whole line:/ > I don't know how to test .BTF . I can only check readelf -S... > > Attached the new patch. > > > From 02afb9417d4f0f8d2175c94fc3797a94a95cc248 Mon Sep 17 00:00:00 2001 > From: Fangrui Song > Date: Mon, 16 Mar 2020 18:02:31 -0700 > Subject: [PATCH bpf v2] bpf: Support llvm-objcopy and llvm-objdump for > vmlinux BTF > > Simplify gen_btf logic to make it work with llvm-objcopy and llvm-objdump. > We use a dd comment to change the e_type field in the ELF header from > ET_EXEC to ET_REL so that .btf.vmlinux.bin.o can be accepted by lld. > > Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux") > Cc: Stanislav Fomichev > Cc: Nick Desaulniers > Reported-by: Nathan Chancellor > Link: https://github.com/ClangBuiltLinux/linux/issues/871 > Signed-off-by: Fangrui Song > --- > scripts/link-vmlinux.sh | 14 +++----------- > 1 file changed, 3 insertions(+), 11 deletions(-) > > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > index dd484e92752e..b23313944c89 100755 > --- a/scripts/link-vmlinux.sh > +++ b/scripts/link-vmlinux.sh > @@ -120,18 +120,10 @@ gen_btf() > > info "BTF" ${2} > vmlinux_link ${1} > - LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} > + ${PAHOLE} -J ${1} I'm not sure why you are touching this line at all. LLVM_OBJCOPY part is necessary, pahole assumes llvm-objcopy by default, but that can (and should for objcopy) be overridden with LLVM_OBJCOPY. > > - # dump .BTF section into raw binary file to link with final vmlinux > - bin_arch=$(LANG=C ${OBJDUMP} -f ${1} | grep architecture | \ > - cut -d, -f1 | cut -d' ' -f2) > - bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \ > - awk '{print $4}') > - ${OBJCOPY} --change-section-address .BTF=0 \ > - --set-section-flags .BTF=alloc -O binary \ > - --only-section=.BTF ${1} .btf.vmlinux.bin > - ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \ > - --rename-section .data=.BTF .btf.vmlinux.bin ${2} > + # Extract .BTF section, change e_type to ET_REL, to link with final vmlinux > + ${OBJCOPY} --only-section=.BTF ${1} ${2} && printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 > } > > # Create ${2} .o file with all symbols from the ${1} object file > -- > 2.25.1.481.gfbce0eb801-goog >