From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) (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 A42CA21C9EB for ; Tue, 6 May 2025 21:41:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746567709; cv=none; b=KGuA8qyDAy3dGTdRPdx0ylT+YJZROUeigQQb1Zas+R8gfFG9FWGBMWBQ+G3+RY+jZPjdZc7vK0/RoYbs/O50kurRb/6ltlODocWdEibnSGvBnVXZefK3vt1CZpUpL5Eb+QYW6Hn/grj3iopbWXFEYgeDZ3imYJwX0f54eqF/a3U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746567709; c=relaxed/simple; bh=9Py2oVLHloj66xUiBl2POuXmO5mcK7wpP1uDUE0NvtM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZMqUbI00J7RUgh2JuxTkCYoqjkJUlNUE2EU+H81AqONEloATkmDYyeWCJuSN3BZcgTEHY/SzVZM97stMnFVJcEcnaFA+viYqxDrV5q2q8mtMZn0xo1MH9wDbZLXUdveww3z5Fyq9F7ld9UdichZyX4Pa75FoR5iygNK9N1y8Q5Y= 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=YDwjjDti; arc=none smtp.client-ip=95.215.58.188 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="YDwjjDti" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1746567694; 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=ReRcs50Y2MVdPcjHGR1u+evgYlPhmw1Q5xKyWbX3gxE=; b=YDwjjDti3JF6hcqRA6FBTwpeyU6orKRjCOb+GtGFeXhi7HZ/9H/5TGf8RCxSasdsqyQY2r q89Km0DLHpywgMuUjwwVyq79HXEkxtk0B/rrbHKnIyDEhLaJfISAXnK/S0h4psT8kdFSCR fGbNjitCmcPwYHbtoX2ejddpzkYytVA= Date: Tue, 6 May 2025 14:41:13 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] bpftool: build bpf bits with -std=gnu11 To: Andrii Nakryiko , =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= Cc: Alexei Starovoitov , Quentin Monnet , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , bpf , LKML References: <20250502085710.3980-1-holger@applied-asynchrony.com> <7326223e-0cb9-4d22-872f-cbf1ff42227d@kernel.org> <913f66a8-6745-0e30-b5b8-96d23bf05b90@applied-asynchrony.com> <2a8208af-bc4b-f1bd-af0b-f5db485ed1f0@applied-asynchrony.com> 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; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2025-05-06 2:04 p.m., Andrii Nakryiko wrote: > On Sun, May 4, 2025 at 3:24 AM Holger Hoffstätte > wrote: >> >> On 2025-05-03 04:36, Alexei Starovoitov wrote: >>> On Fri, May 2, 2025 at 2:53 AM Holger Hoffstätte >>> wrote: >>>> >>>> On 2025-05-02 11:26, Quentin Monnet wrote: >>>>> On 02/05/2025 09:57, Holger Hoffstätte wrote: >>>>>> A gcc-15-based bpf toolchain defaults to C23 and fails to compile various >>>>>> kernel headers due to their use of a custom 'bool' type. >>>>>> Explicitly using -std=gnu11 works with both clang and bpf-toolchain. >>>>>> >>>>>> Signed-off-by: Holger Hoffstätte >>>>> >>>>> Thanks! I tested that it still works with clang. >>>>> >>>>> Acked-by: Quentin Monnet >>>> >>>> Thanks! >>>> >>>>> I didn't manage to compile with gcc, though. I tried with gcc 15.1.1 but >>>>> option '--target=bpf' is apparently unrecognised by the gcc version on >>>>> my setup. >>>>> >>>>> Out of curiosity, how did you build using gcc for the skeleton? Was it >>>>> enough to run "CLANG=gcc make"? Does it pass the clang-bpf-co-re build >>>>> probe successfully? >>>> >>>> I'm on Gentoo where we have a gcc-14/15 based "bpf-toolchain" package, >>>> which is just gcc configured & packaged for the bpf target. >>>> Our bpftool package can be built with clang (default) or without, in >>>> which case it depend on the bpf-toolchain. The idea is to gradually >>>> allow bpf/xdp tooling to build/run without requiring clang. >>>> >>>> The --target definition is conditional and removed when not using clang: >>>> https://gitweb.gentoo.org/repo/gentoo.git/tree/dev-util/bpftool/bpftool-7.5.0.ebuild?id=bf70fbf7b0dc97fbc97af579954ea81a8df36113#n94 >>>> >>>> The bug for building with the new gcc-15 based toolchain where this >>>> patch originated is here: https://bugs.gentoo.org/955156 >>> >>> So you're fixing this build error: >>> >>> bpf-unknown-none-gcc \ >>> -I. \ >>> -I/var/tmp/portage/dev-util/bpftool-7.5.0/work/bpftool-libbpf-v7.5.0-sources/include/uapi/ >>> \ >>> -I/var/tmp/portage/dev-util/bpftool-7.5.0/work/bpftool-libbpf-v7.5.0-sources/src/bootstrap/libbpf/include >>> \ >>> -g -O2 -Wall -fno-stack-protector \ >>> -c skeleton/profiler.bpf.c -o profiler.bpf.o >>> In file included from skeleton/profiler.bpf.c:3: >>> ./vmlinux.h:5: warning: ignoring '#pragma clang attribute' [-Wunknown-pragmas] >>> 5 | #pragma clang attribute push >>> (__attribute__((preserve_access_index)), apply_to = record) >>> ./vmlinux.h:9845:9: error: cannot use keyword 'false' as enumeration constant >>> 9845 | false = 0, >>> | ^~~~~ >>> ./vmlinux.h:9845:9: note: 'false' is a keyword with '-std=c23' onwards >>> ./vmlinux.h:31137:15: error: 'bool' cannot be defined via 'typedef' >>> 31137 | typedef _Bool bool; >>> | ^~~~ >>> >>> with -std=gnu11 flag and >> >> Yes, correct. This is the same as all over the kernel or the bpf tests >> for handling C23. I fully understand that this particular patch is only >> one piece of the puzzle. >> > > What's the best way to detect (at compile time) whether bool, false, > and true are treated as reserved keywords? To solve this properly > vmlinux.h would have to be adjusted by vmlinux.h to avoid emitting > bool/false/true *iff* compiler version/mode doesn't like that I ran into this when adding GCC BPF to CI [1]. One can do something like: #if __STDC_VERSION__ < 202311L enum { false = 0, true = 1, }; #endif But in case of vmlinux.h this would require hacking bpftool, and so for selftests/bpf we decided to pass -std=gnu11 [2]. [1] https://lore.kernel.org/bpf/CAADnVQKNqdLW1bpvCpVV3yNizwra0cCkBnAbsNp3rTmi8WFcvQ@mail.gmail.com/ [2] https://lore.kernel.org/bpf/20250107235813.2964472-1-ihor.solodrai@pm.me/ > >>> ignoring an important warning ? >> >> Nobody is (or was) ignoring the warning - it was under discussion when >> I posted the patch. After reaching out to Oracle to verify, we have now >> added the BPF_NO_PRESERVE_ACCESS_INDEX define when building with gcc-bpf; >> this resolves the warning, just like in the bpf self-tests. >> >> You are right that such an addition to the in-kernel bpftool build is >> still missing. If you have a suggestion on how best to do that via the >> existing Makefile I'm all ears. >> >> As for the remaining warnings - we are also very aware of the ongoing >> upstream work to support btf_type_tag: >> https://gcc.gnu.org/pipermail/gcc-patches/2025-April/682340.html. >> >>> End result: partially functional bpftool, >>> and users will have no idea why some features of bpftool are not working. >> >> First of all this is never shipped to any users; using gcc-bpf requires >> active opt-in by developers or users, and now also warns that such a setup >> may result in unexpected bugs due to ongoing work in both Linux and bpftool. >> Like I said before, by default everyone builds with clang and that is also >> true for our distributed binaries. >> >> If you think adding the -std=gnu11 bit is inappropriate at this time then >> just ignore this patch for now. Sooner or later the bpftool build will have >> to be adapted with BPF_CFLAGS (liek in the selftests) and hopefuilly an >> abstracted BPF_CC so that we no longer have to pretend to be clang when >> using gcc. >> >> cheers >> Holger