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=-18.9 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 4555FC1975A for ; Tue, 17 Mar 2020 20:58:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E190620738 for ; Tue, 17 Mar 2020 20:58:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Yj2Pge8n" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726680AbgCQU6j (ORCPT ); Tue, 17 Mar 2020 16:58:39 -0400 Received: from mail-pj1-f68.google.com ([209.85.216.68]:55046 "EHLO mail-pj1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726721AbgCQU6j (ORCPT ); Tue, 17 Mar 2020 16:58:39 -0400 Received: by mail-pj1-f68.google.com with SMTP id np9so280300pjb.4 for ; Tue, 17 Mar 2020 13:58:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=KCBhhTAcVEBazgsEE9+FOciZw820M7vK8so1wHzYoPU=; b=Yj2Pge8n4yjbWrv/Jh/jCeTu0RkzZqFhMrixm4osMGeB63G0yyndfaGCEtUd7D9o9T wuh+Qi/xmwpnCzB/wyFZKIz7G9OhV9Pj2tZ+9KEMZqzOoX6SAKhTt8nekJfFeHZKHY4u NoNZUUP3wAAseC2hB8zB8nWff6ZxlIO3IKozCQoTtso0zxXvhX872sy1TKqVfrff2znU QnKwq9Fc75CX2NK7gCcDSxsrMtwDfV+4AB7Qv5FhBcfw/Iw6AaDzPbz0eZg/Vgq4nLoQ wtBt8FKlT6Qr5jHjmwhhGGRwlXN+8etQw2vUgvmIAJuuAnNLhGNZe5qouF8kVryn7w2a jl/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=KCBhhTAcVEBazgsEE9+FOciZw820M7vK8so1wHzYoPU=; b=WxVZLd7COVwC1lz9sBvBarkgmY/oWy2uGVIcKwmICA4bDIqxbj4s/Y4//MmwDL0yNN oIBYLuLIET5QINg28V5BB3aksDCYCIlCdsEG6rFcbMNb3k6BFlspNUXa8+V1PzoE0Z7x pAL52rhYna8lMY66QSqjgE4l9aJY9rwMeT0ZKz5DHFj/sYo/HdGe5jO6mp+vXkb9WkQE HwH0+PkshdZmjcQNxoS12eESdoC+dUqf1I6PIYfxrGWMtr3gD9rrraV656qhRloYn31g 3G3Z1crfXhKPMmbzB6A39npcq4HftMeZPtYfICudezNH0DsjaLNNHvAVzSKEKcB7tdIS gLpw== X-Gm-Message-State: ANhLgQ1Gl6KSheoTFUnSlbvmxku8MVxnkau9JBpLt8SafEaajTvIlWCh uN8S9Tdi2GrTbiG/nq49jHndcyO+mXXrhqAN X-Google-Smtp-Source: ADFU+vs5FTntT2fltMgq8XWx3tivOdhnOA72pkcf2nxCBIlptUhCjSxQK07e4IjdG6QOSwBAr4j39Q== X-Received: by 2002:a17:90b:238e:: with SMTP id mr14mr1149466pjb.146.1584478716324; Tue, 17 Mar 2020 13:58:36 -0700 (PDT) Received: from google.com ([2620:15c:2ce:0:9efe:9f1:9267:2b27]) by smtp.gmail.com with ESMTPSA id w205sm4108803pfc.75.2020.03.17.13.58.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Mar 2020 13:58:35 -0700 (PDT) Date: Tue, 17 Mar 2020 13:58:32 -0700 From: Fangrui Song To: bpf , Networking Cc: Andrii Nakryiko , Daniel Borkmann , Nick Desaulniers , Nathan Chancellor , clang-built-linux@googlegroups.com, Stanislav Fomichev , "David S. Miller" , Alexei Starovoitov , Kees Cook Subject: [PATCH bpf-next v4] bpf: Support llvm-objcopy and llvm-objdump for vmlinux BTF Message-ID: <20200317205832.lna5phig2ed3bf2n@google.com> References: <20200317011654.zkx5r7so53skowlc@google.com> <20200317033701.w7jwos7mvfnde2t2@google.com> <20200317052120.diawg3a75kxl5hkn@google.com> <20200317054359.snyyojyf6gjxufij@google.com> <20200317162405.GB2459609@mini-arch.hsd1.ca.comcast.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20200317162405.GB2459609@mini-arch.hsd1.ca.comcast.net> Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 2020-03-17, Stanislav Fomichev wrote: >On 03/16, Fangrui Song wrote: >> On 2020-03-16, Andrii Nakryiko wrote: >> > On Mon, Mar 16, 2020 at 10:21 PM Fangrui Song wrote: >> > > >> > > >> > > On 2020-03-16, Andrii Nakryiko wrote: >> > > >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 ${1} >> > > > >> > > >I'm not sure why you are touching this line at all. LLVM_OBJCOPY part >> > > >is necessary, pahole assumes llvm-objcopy by default, but that can >> > > >(and should for objcopy) be overridden with LLVM_OBJCOPY. >> > > >> > > Why is LLVM_OBJCOPY assumed? What if llvm-objcopy is not available? >> > >> > It's pahole assumption that we have to live with. pahole assumes >> > llvm-objcopy internally, unless it is overriden with LLVM_OBJCOPY env >> > var. So please revert this line otherwise you are breaking it for GCC >> > objcopy case. >> >> Acknowledged. Uploaded v3. >> >> I added back 2>/dev/null which was removed by a previous change, to >> suppress GNU objcopy warnings. The warnings could be annoying in V=1 >> output. >> >> > > This is confusing that one tool assumes llvm-objcopy while the block >> > > below immediately uses GNU objcopy (without this patch). >> > > >> > > e83b9f55448afce3fe1abcd1d10db9584f8042a6 "kbuild: add ability to >> > > generate BTF type info for vmlinux" does not say why LLVM_OBJCOPY is >> > > set. >> > > >> > > >> >> > > >> - # dump .BTF section into raw binary file to link with final vmlinux >> > > >> - bin_arch=$(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 >> > > >> >> >> From ca3597477542453e9f63185c27c162da081a4baf Mon Sep 17 00:00:00 2001 >> From: Fangrui Song >> Date: Mon, 16 Mar 2020 22:38:23 -0700 >> Subject: [PATCH bpf v3] bpf: Support llvm-objcopy and llvm-objdump for >> vmlinux BTF >> >> Simplify gen_btf logic to make it work with llvm-objcopy and llvm-objdump. >> Add 2>/dev/null to suppress GNU objcopy (but not llvm-objcopy) warnings >> "empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?" >> Our use of --only-section drops many SHF_ALLOC sections which will essentially nullify >> program headers. When used as linker input, program headers are simply >> ignored. >> >> We use a dd command 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. >> Accepting ET_EXEC as an input file is an extremely rare GNU ld feature >> that lld does not intend to support, because this is very error-prone. >> >> 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 | 12 ++---------- >> 1 file changed, 2 insertions(+), 10 deletions(-) >> >> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh >> index dd484e92752e..c3e808a89d4a 100755 >> --- a/scripts/link-vmlinux.sh >> +++ b/scripts/link-vmlinux.sh >> @@ -122,16 +122,8 @@ gen_btf() >> vmlinux_link ${1} >> LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} >> - # dump .BTF section into raw binary file to link with final vmlinux >> - bin_arch=$(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} ${2} 2> /dev/null && printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 >No, it doesn't work unfortunately, I get "in-kernel BTF is malformed" >from the kernel. > >I think that's because -O binary adds the following: >$ nm .btf.vmxlinux.bin >00000000002f7bc9 D _binary__btf_vmlinux_bin_end >00000000002f7bc9 A _binary__btf_vmlinux_bin_size >0000000000000000 D _binary__btf_vmlinux_bin_start > >While non-binary mode doesn't: >$ nm .btf.vmxlinux.bin > >We don't add them manually in the linker map and expect objcopy to add >them, see: >https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/kernel/bpf/btf.c#n3480 Attached v4. * Added status=none to the dd command to suppress stderr output. * `objcopy -I binary` synthesized symbols are only used in BTF, not elsewhere. I think we can replace it with a more common trick, __start_$sectionname __stop_$sectionname. * GNU ld<2.23 can define __start_BTF and __stop_BTF as SHN_ABS. I think it is totally fine for a SHN_ABS symbol to be referenced by an R_X86_64_32S (absolute relocation), but arch/x86/tools/relocs.c contains an unnecessarily rigid check that rejects this. ... Invalid absolute R_X86_64_32S relocation: __start_BTF make[3]: *** [arch/x86/boot/compressed/Makefile:123: arch/x86/boot/compressed/vmlinux.relocs] Error 1 Since we are going to bump binutils version requirement to 2.23, which will completely avoid the issue. I will not mention it again. https://lore.kernel.org/lkml/202003161354.538479F16@keescook/ * I should mention that an orphan BTF (previously .BTF) could trigger a --orphan-handling=warn warning. So eventually we might need to add an output section description BTF : { *(BTF) } to the vmlinux linker script for every arch. I'll not do that in this patch, though. > >> } >> # Create ${2} .o file with all symbols from the ${1} object file >> -- >> 2.25.1.481.gfbce0eb801-goog >> From 9b694d68fefe041464eccb948f6d246fab67942d Mon Sep 17 00:00:00 2001 From: Fangrui Song Date: Tue, 17 Mar 2020 13:51:04 -0700 Subject: [PATCH bpf-next v4] bpf: Support llvm-objcopy and llvm-objdump for vmlinux BTF Simplify gen_btf logic to make it work with llvm-objcopy and llvm-objdump. The existing 'file format' and 'architecture' parsing logic is brittle and does not work with llvm-objcopy/llvm-objdump. .BTF in .tmp_vmlinux.btf is non-SHF_ALLOC. Add the SHF_ALLOC flag and rename .BTF to BTF so that C code can reference the section via linker synthesized __start_BTF and __stop_BTF. This fixes a small problem that previous .BTF had the SHF_WRITE flag. Additionally, `objcopy -I binary` synthesized symbols _binary__btf_vmlinux_bin_start and _binary__btf_vmlinux_bin_start (not used elsewhere) are replaced with more common __start_BTF and __stop_BTF. Add 2>/dev/null because GNU objcopy (but not llvm-objcopy) warns "empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?" We use a dd command to change the e_type field in the ELF header from ET_EXEC to ET_REL so that lld will accept .btf.vmlinux.bin.o. Accepting ET_EXEC as an input file is an extremely rare GNU ld feature that lld does not intend to support, because this is error-prone. 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 --- kernel/bpf/btf.c | 9 ++++----- kernel/bpf/sysfs_btf.c | 11 +++++------ scripts/link-vmlinux.sh | 16 ++++++---------- 3 files changed, 15 insertions(+), 21 deletions(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 787140095e58..51fff49de561 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -3477,8 +3477,8 @@ static struct btf *btf_parse(void __user *btf_data, u32 btf_data_size, return ERR_PTR(err); } -extern char __weak _binary__btf_vmlinux_bin_start[]; -extern char __weak _binary__btf_vmlinux_bin_end[]; +extern char __weak __start_BTF[]; +extern char __weak __stop_BTF[]; extern struct btf *btf_vmlinux; #define BPF_MAP_TYPE(_id, _ops) @@ -3605,9 +3605,8 @@ struct btf *btf_parse_vmlinux(void) } env->btf = btf; - btf->data = _binary__btf_vmlinux_bin_start; - btf->data_size = _binary__btf_vmlinux_bin_end - - _binary__btf_vmlinux_bin_start; + btf->data = __start_BTF; + btf->data_size = __stop_BTF - __start_BTF; err = btf_parse_hdr(env); if (err) diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c index 7ae5dddd1fe6..3b495773de5a 100644 --- a/kernel/bpf/sysfs_btf.c +++ b/kernel/bpf/sysfs_btf.c @@ -9,15 +9,15 @@ #include /* See scripts/link-vmlinux.sh, gen_btf() func for details */ -extern char __weak _binary__btf_vmlinux_bin_start[]; -extern char __weak _binary__btf_vmlinux_bin_end[]; +extern char __weak __start_BTF[]; +extern char __weak __stop_BTF[]; static ssize_t btf_vmlinux_read(struct file *file, struct kobject *kobj, struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len) { - memcpy(buf, _binary__btf_vmlinux_bin_start + off, len); + memcpy(buf, __start_BTF + off, len); return len; } @@ -30,15 +30,14 @@ static struct kobject *btf_kobj; static int __init btf_vmlinux_init(void) { - if (!_binary__btf_vmlinux_bin_start) + if (!__start_BTF) return 0; btf_kobj = kobject_create_and_add("btf", kernel_kobj); if (!btf_kobj) return -ENOMEM; - bin_attr_btf_vmlinux.size = _binary__btf_vmlinux_bin_end - - _binary__btf_vmlinux_bin_start; + bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF; return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux); } diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index dd484e92752e..c0d2ecf1bff7 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -122,16 +122,12 @@ gen_btf() vmlinux_link ${1} LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} - # dump .BTF section into raw binary file to link with final vmlinux - bin_arch=$(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, add SHF_ALLOC, rename to BTF so that we can reference + # it via linker synthesized __start_BTF and __stop_BTF. Change e_type + # to ET_REL so that it can be used to link final vmlinux. + ${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \ + --rename-section .BTF=BTF ${1} ${2} 2>/dev/null && \ + printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none } # Create ${2} .o file with all symbols from the ${1} object file -- 2.25.1.481.gfbce0eb801-goog