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=-8.5 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT 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 716A4C43381 for ; Thu, 21 Mar 2019 00:03:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2EA8A218AE for ; Thu, 21 Mar 2019 00:03:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=fomichev-me.20150623.gappssmtp.com header.i=@fomichev-me.20150623.gappssmtp.com header.b="TsrdLzHS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727685AbfCUADM (ORCPT ); Wed, 20 Mar 2019 20:03:12 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:42179 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726914AbfCUADM (ORCPT ); Wed, 20 Mar 2019 20:03:12 -0400 Received: by mail-pg1-f196.google.com with SMTP id p6so2944268pgh.9 for ; Wed, 20 Mar 2019 17:03:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fomichev-me.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=v4BtjpfJbO6gNMqHIipAkUB/MOhgl1tTQ8tnCWq1LVg=; b=TsrdLzHSRUS6UwZIUjQRDQn1GKfLTSS6q4jwNO2D+ghu2m6iNvqVegqvEzu+PNXbCd 2RC1mDqpplTThcdUzeiWiyK9EqXucc5pIjio/2ggcXRowiJzvmva+iWqQC7zE1tRneOy NCF1eRX22q9Yept60Yc5Y/4uPQMAIHX/Tm76PMA+5IBJhVJo7kM8qG174sjwdbdsAUNX WdkeRuODfMbPphDH7G82ZNbUI76jbsXkT+hBP/iLFwC4qmXxOreuRPf4om7BRasalULK low1b4kTVH/aKUnYsFZRddImecvmuLe+2RzgelGR7APH/FwluLkH+yVRsPkp0PoEj/Z6 dUOg== 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:user-agent; bh=v4BtjpfJbO6gNMqHIipAkUB/MOhgl1tTQ8tnCWq1LVg=; b=EUkju4RZCn/+xMbbNsNLyBDpypZ+EB3KVo2pxQI9Xn1cpluIqBN6EdMEPD7bKXXFw6 294eVtXntllw2/ioXM8ya9XBn3iaDcVsLUhXT8gtG2N/xVLG+dYsvTRIczXeK0P7FPFv +s9EO6tSS2Mj0gAOXG8lgvtADF2zjHpdJn6KFQ/KFz5bzFgXO68ddwbmTTqfVXp4cVrl /higHzuvefGb9kOmKQpgiSQtiFsEkA7Q+x48j6Ozpaecg/T255g26rQK1tJdHtFRy6Y7 ymOnEATRXXZGmRgtX0/v9nrYzzcTv2jnOBv09LtFKbzBZNAcqfVGg0VYUY5Uq/U9wV+4 Ilzw== X-Gm-Message-State: APjAAAUjQN+1x6fjFPLq/TA6TsOu9Ft3iH5fUzN6D8vu2f7p8gcrssrc RYfebX3BveDcZZuuCtJ9/YrnIg== X-Google-Smtp-Source: APXvYqyUlCu7TMsrwcxgIZzLZKYOSeMFQJ+KeDuEBI/oherkNnZfqNpRuSrbICH/545dmMrc2sF3Pw== X-Received: by 2002:a63:f541:: with SMTP id e1mr660666pgk.388.1553126590892; Wed, 20 Mar 2019 17:03:10 -0700 (PDT) Received: from localhost ([2601:646:8f00:18d9:d0fa:7a4b:764f:de48]) by smtp.gmail.com with ESMTPSA id s79sm6292014pfa.61.2019.03.20.17.03.09 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 20 Mar 2019 17:03:10 -0700 (PDT) Date: Wed, 20 Mar 2019 17:03:09 -0700 From: Stanislav Fomichev To: Daniel Borkmann Cc: Yonghong Song , Sergey Senozhatsky , Shuah Khan , Alexei Starovoitov , Stanislav Fomichev , Martin Lau , Song Liu , "linux-kselftest@vger.kernel.org" , "netdev@vger.kernel.org" , "bpf@vger.kernel.org" Subject: Re: [PATCHv2 bpf-next 1/3] bpf, tests: tweak endianness selection Message-ID: <20190321000309.GR7431@mini-arch.hsd1.ca.comcast.net> References: <20190320125335.19621-1-sergey.senozhatsky@gmail.com> <20190320171332.GJ7431@mini-arch.hsd1.ca.comcast.net> <4c6db4e5-8e77-2e01-a4ab-25808df2b857@fb.com> <20190320222759.GQ7431@mini-arch.hsd1.ca.comcast.net> <55387960-b50a-2f5f-1083-da2377558c2b@fb.com> <8ab21b4e-885d-e91e-1614-f1b15660ce4c@iogearbox.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8ab21b4e-885d-e91e-1614-f1b15660ce4c@iogearbox.net> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 03/21, Daniel Borkmann wrote: > On 03/20/2019 11:45 PM, Yonghong Song wrote: > > On 3/20/19 3:27 PM, Stanislav Fomichev wrote: > >> On 03/20, Yonghong Song wrote: > >>> On 3/20/19 10:13 AM, Stanislav Fomichev wrote: > >>>> On 03/20, Sergey Senozhatsky wrote: > >>>>> Not all compilers have __builtin_bswap16() and __builtin_bswap32(), > >>>>> thus not all compilers are able to compile the following code: > >>>>> > >>>>> (__builtin_constant_p(x) ? \ > >>>>> ___constant_swab16(x) : __builtin_bswap16(x)) > >>>>> > >>>>> That's the reason why bpf_ntohl() doesn't work on GCC < 4.8, for > >>>>> instance: > >>>>> > >>>>> error: implicit declaration of function '__builtin_bswap16' > >>>>> > >>>>> We can use __builtin_bswap16() only if compiler has this built-in, > >>>>> that is, only if __HAVE_BUILTIN_BSWAP16__ is defined. Standard UAPI > >>>>> __swab16()/__swab32() take care of that, and, additionally, handle > >>>>> __builtin_constant_p() cases as well: > >>>>> > >>>>> #ifdef __HAVE_BUILTIN_BSWAP16__ > >>>>> #define __swab16(x) (__u16)__builtin_bswap16((__u16)(x)) > >>>>> #else > >>>>> #define __swab16(x) \ > >>>>> (__builtin_constant_p((__u16)(x)) ? \ > >>>>> ___constant_swab16(x) : \ > >>>>> __fswab16(x)) > >>>>> #endif > >>>>> > >>>>> So we can tweak selftests/bpf/bpf_endian.h and use UAPI > >>>>> __swab16()/__swab32(). > >>>>> > >>>>> Signed-off-by: Sergey Senozhatsky > >>>>> --- > >>>>> > >>>>> v2: fixed build error, reshuffled patches (Stanislav Fomichev) > >>>> Tested them locally with the compiler I saw the initial issues with - all > >>>> fine, I don't see any errors with the older gcc. > >>>> > >>>> One last question I have is: what happens in the llvm+bpf case? Have > >>>> you tested that? I think LLVM has all the builtins required, but since > >>>> we are relying on the swab.h now (and it relies on > >>>> __HAVE_BUILTIN_BSWAP16__), I wonder whether this detection works > >>>> correctly on the llvm when targeting bpf. (sidenote: bpf_endian.h can be > >>>> used from both userspace and bpf programs). > >>> > >>> Inside kernel clang compiler header (linux/compiler-clang.h) does not > >>> define __HAVE_BUILTIN_BSWAP16__. So it will go to the "else" branch in > >>> the above. So I think it should work with clang + bpf. > >> Hm, isn't it the opposite of what we want then? I think for llvm+bpf we always > >> want to use the builtins to make it properly generate > >> BPF_TO_BE/BPF_TO_LE instructions. > > > > Okay, I see. Then this patch will not achieve that. > > The following are two common ways to compile a bpf program: > > - "clang -target bpf ...", maybe add macro __BPF__ somewhere > > to indicate builtin_bswap16 always available? > > - "clang ..." and then "llc -march=bpf ..." > > in this case, __BPF__ macro is not available and > > we will not be able to use builtin swap for bpf program. > > > > Maybe use __clang__ macro (or gcc macro) to distinguish between clang > > and gcc. If it is gcc we will check builtin availability, otherwise, > > we assume builtin always available? This not pretty though. > > I think the way this should be fixed is the following: In case > of LLVM (aka compiling BPF prog), we want the code to be as-is, > in case if gcc is compiling the hostprog, we either want to keep > using __builtin_bswap16() or fall-back to something else. Thus, > I would suggest, we add a new feature test for tooling infra under > tools/build/feature/ that compiles a dummy prog with __builtin_bswap16(). > And in the bpf_endian.h we define __bpf_ntohs(x) to __bpf_swab16(x) > which either resolves to __builtin_bswap16() or some fallback > implementation if not available. I don't think there should be much > of an issue and it would follow the standard way to do it. It's not as easy as llvm vs gcc. We can compile userland tests with llvm/clang as well. We really need to distinguish between the target: bfp vs non-bpf: always use builtins in bpf case and fallback to swab.h for userland (or use feature detection, but swab.h should be enough in theory). Can we rely on __bpf__ define? $ cat tmp.c #ifdef __bpf__ #error a #else #error b #endif $ clang -c -target bpf tmp.c tmp.c:2:2: error: a #error a ^ 1 error generated. > > >>>>> tools/testing/selftests/bpf/bpf_endian.h | 8 ++++---- > >>>>> 1 file changed, 4 insertions(+), 4 deletions(-) > >>>>> > >>>>> diff --git a/tools/testing/selftests/bpf/bpf_endian.h b/tools/testing/selftests/bpf/bpf_endian.h > >>>>> index b25595ea4a78..1ed268b2002b 100644 > >>>>> --- a/tools/testing/selftests/bpf/bpf_endian.h > >>>>> +++ b/tools/testing/selftests/bpf/bpf_endian.h > >>>>> @@ -20,12 +20,12 @@ > >>>>> * use different targets. > >>>>> */ > >>>>> #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ > >>>>> -# define __bpf_ntohs(x) __builtin_bswap16(x) > >>>>> -# define __bpf_htons(x) __builtin_bswap16(x) > >>>>> +# define __bpf_ntohs(x) __swab16(x) > >>>>> +# define __bpf_htons(x) __swab16(x) > >>>>> # define __bpf_constant_ntohs(x) ___constant_swab16(x) > >>>>> # define __bpf_constant_htons(x) ___constant_swab16(x) > >>>>> -# define __bpf_ntohl(x) __builtin_bswap32(x) > >>>>> -# define __bpf_htonl(x) __builtin_bswap32(x) > >>>>> +# define __bpf_ntohl(x) __swab32(x) > >>>>> +# define __bpf_htonl(x) __swab32(x) > >>>>> # define __bpf_constant_ntohl(x) ___constant_swab32(x) > >>>>> # define __bpf_constant_htonl(x) ___constant_swab32(x) > >>>>> #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ > >>>>> -- > >>>>> 2.21.0 > >>>>> >