From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2A014175A72 for ; Mon, 2 Mar 2026 22:42:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.184 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772491351; cv=none; b=B7AT4pBL7jKMai2YthiE+w8auGJeoyfj2hCrMEGxdkFkhEvj1DkyYLN9ePlqVvLKWH63ln9BIj2zYxnnBqnwKANMMuRRFUjNRsu3Xf6Hz9vSBoud1oBBlf+p7egOHuwxp7qPz+tWW09r12AsQAogvkzPsIAAWCLAW+aoy8uwFTI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772491351; c=relaxed/simple; bh=uIXxlCxM8K3KnIfXGOIzqjKsZTq3mjFUNPh4aMH4+eM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=turcvftrLcxuYpF3QeLkWJjhNpb/pPtT9g+x6Uke98S/RnrlbtC1NcuFaCdDh7b+9Ghp2wPaJykLQeln/zNSqDYOVLa6yyMJc7p3win3oTasfh7Ghm7/wuWm09faof6kOu6R22xQLOu67D5guyxeLUnHL13e6o285bkWtzOvTPQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=PZNeNCNM; arc=none smtp.client-ip=91.218.175.184 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="PZNeNCNM" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772491338; 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=hGo15nkryHUBkHLvQKlc3e8ZpSUBd+CCPOefqDJ25zk=; b=PZNeNCNMtO+jzv87j1MV/ETBDAwHXuqaspsSLVEI2WpHy5e+DOMa3+DncMn82JQocJnPZE DrmlgSABp599yyHY6g8URW3QQ9sN/h27Dz6nVc3PSNoJ+bz4dshcTv/UFIJKj2oCQuBhJ1 ko6z0yOqQaLWLYh2RzUlACh58QgepKU= Date: Mon, 2 Mar 2026 14:42:11 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf v3 01/15] selftests/bpf: Pass through build flags to bpftool and resolve_btfids To: Vitaly Chikunov Cc: bot+bpf-ci@kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, olsajiri@gmail.com, yatsenko@meta.com, alexis.lothore@bootlin.com, ameryhung@gmail.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, martin.lau@kernel.org, yonghong.song@linux.dev, clm@meta.com References: <20260220222604.1155148-2-ihor.solodrai@linux.dev> <789af3df-291c-410d-89d8-ee7b12479798@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ihor Solodrai In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 3/2/26 12:27 PM, Vitaly Chikunov wrote: > Ihor, > > On Mon, Mar 02, 2026 at 10:01:59AM -0800, Ihor Solodrai wrote: >> On 3/2/26 7:22 AM, Vitaly Chikunov wrote: >>> On Fri, Feb 20, 2026 at 08:23:51PM -0800, Ihor Solodrai wrote: >>>> On 2/20/26 2:57 PM, bot+bpf-ci@kernel.org wrote: >>>>>> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile >>>>>> index 1733a6e93a07..ef083602b73a 100644 >>>>>> --- a/tools/bpf/resolve_btfids/Makefile >>>>>> +++ b/tools/bpf/resolve_btfids/Makefile >>>>>> @@ -65,6 +65,9 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU >>>>>> LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null) >>>>>> LIBELF_LIBS := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf) >>>>>> >>>>>> +ZLIB_LIBS := $(shell $(HOSTPKG_CONFIG) zlib --libs 2>/dev/null || echo -lz) >>>>>> +ZSTD_LIBS := $(shell $(HOSTPKG_CONFIG) libzstd --libs 2>/dev/null || echo -lzstd) >>>>> >>>>> The "|| echo -lzstd" fallback makes zstd an unconditional link >>>>> dependency. On systems where libzstd-dev is not installed, pkg-config >>>>> fails and the fallback provides -lzstd, but the linker cannot find the >>>>> library and the build fails. >>>>> >>>>> bpftool handles the same transitive dependency conditionally via a >>>>> feature test: >>>>> >>>>> tools/bpf/bpftool/Makefile: >>>>> ifeq ($(feature-libelf-zstd),1) >>>>> LIBS += -lzstd >>>>> LIBS_BOOTSTRAP += -lzstd >>>>> endif >>>>> >>>>> Would it be safer to drop the fallback here so ZSTD_LIBS is empty >>>>> when zstd is not available? >>>>> >>>>> ZSTD_LIBS := $(shell $(HOSTPKG_CONFIG) libzstd --libs 2>/dev/null) >>>>> >>>>> This would still link zstd when present (needed for the static linking >>>>> case where libelf.a pulls in ZSTD symbols from elf_compress.o), but >>>>> avoid breaking dynamic builds on systems without libzstd-dev. >>>> >>>> [...] >>>> >>>> >>>> So, while AI may be technically correct that the build will fail if >>>> libelf is installed and libzstd is not, it seems a far-fetched >>>> situation, given that libelf depends on libzstd. >>> >>> This is not far-fetched, and we have build failure for v7.0-rc2 due to >>> this. >>> >>> ld: cannot find -lzstd: No such file or directory >>> >>> Even though libelf is linked with libzstd, this does not imply >>> libzstd-devel (with headers and so library) is there when building. >> >> Does AI's suggestion make sense in your case then? >> That is, make ZSTD_LIBS empty in case pkg-config didn't find libzstd? >> >> I'm happy to fix this, the build shouldn't fail unless it must. >> >> But I am curious how and why an environment building Linux with BTF >> (requiring build and run of resolve_btfids), which needs libelf-dev >> and presumably its dependencies, would exclude/avoid installing >> libzstd-dev? > > Are you providing -lzstd just to link with libelf? I don't think you need to An explicit -lzstd flag was added to enable a static build [1]. > care about zstd in that case. libelf is already linked with libzstd. If you > don't use libzstd functions yourself you don't need to link with -lzstd. > > Example build without -lzstd: > > builder@x86_64:~/RPM/BUILD/kernel-image-7.0-rc2$ grep zstd tools/bpf/resolve_btfids/Makefile > ZSTD_LIBS := $(shell $(HOSTPKG_CONFIG) libzstd --libs 2>/dev/null) > > builder@x86_64:~/RPM/BUILD/kernel-image-7.0-rc2$ ldd ./tools/bpf/resolve_btfids/resolve_btfids > linux-vdso.so.1 (0x00007ff8b2329000) > libelf.so.1 => /lib64/libelf.so.1 (0x00007ff8b2287000) > libz.so.1 => /lib64/libz.so.1 (0x00007ff8b2269000) > libc.so.6 => /lib64/libc.so.6 (0x00007ff8b206e000) > libzstd.so.1 => /lib64/libzstd.so.1 (0x00007ff8b1fc8000) > /lib64/ld-linux-x86-64.so.2 (0x00007ff8b232b000) > builder@x86_64:~/RPM/BUILD/kernel-image-7.0-rc2$ rpm -q libzstd > libzstd-1.5.5-alt2.x86_64 > builder@x86_64:~/RPM/BUILD/kernel-image-7.0-rc2$ rpm -q libzstd-devel > package libzstd-devel is not installed > > lib*-devel/-dev packages only required if your source is directly using the > target lib, in other causes this is already handled. The issue that AI has raised is whether to leave -lzstd link flag by default or not. I decided to leave it on the assumption that the environments building Linux with BTF (hence building and running resovle_btfids) would have libelf-dev installed (because -lelf has been a requirement forever [2]), and libzstd-dev is its dependency. I checked a few recent distros, all of them have libzstd-dev as a direct dependency of libelf-dev, which supports my assumption: # Fedora $ dnf repoquery --providers-of=depends elfutils-libelf-devel Updating and loading repositories: Repositories loaded. elfutils-libelf-0:0.194-1.fc43.i686 elfutils-libelf-0:0.194-1.fc43.x86_64 libzstd-devel-0:1.5.7-2.fc43.i686 libzstd-devel-0:1.5.7-2.fc43.x86_64 pkgconf-pkg-config-0:2.3.0-3.fc43.i686 pkgconf-pkg-config-0:2.3.0-3.fc43.x86_64 zlib-ng-compat-devel-0:2.3.3-1.fc43.i686 zlib-ng-compat-devel-0:2.3.3-1.fc43.x86_64 # Ubuntu $ apt info libelf-dev Package: libelf-dev Version: 0.190-1.1ubuntu0.1 Priority: optional Section: libdevel Source: elfutils Origin: Ubuntu Maintainer: Ubuntu Developers Original-Maintainer: Debian Elfutils Maintainers Bugs: https://bugs.launchpad.net/ubuntu/+filebug Installed-Size: 385 kB Depends: libelf1t64 (= 0.190-1.1ubuntu0.1), zlib1g-dev, libzstd-dev Conflicts: libelfg0-dev [...] # Debian $ apt info libelf-dev Package: libelf-dev Version: 0.192-4 Priority: optional Section: libdevel Source: elfutils Maintainer: Debian Elfutils Maintainers Installed-Size: 420 kB Depends: libelf1t64 (= 0.192-4), zlib1g-dev, libzstd-dev Conflicts: libelfg0-dev [...] Of course it's plausible to have a system where libelf-dev is present while libzstd-dev is not, as demonstrated by you running one. Anyways this is easy to fix, I'll send a patch shortly. [1] https://lore.kernel.org/bpf/4ff82800-2daa-4b9f-95a9-6f512859ee70@linux.dev/ [2] https://lore.kernel.org/bpf/20200711215329.41165-2-jolsa@kernel.org/ > > Thanks, > >> >> Thanks. >> >>> >>> Thanks, >>> >>>> >>>> I think we can leave the default -lzstd to have an explicit >>>> dependency in the Makefile. >>>> >>>> >>>>> >>>>> [ ... ] >>