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=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 B4B00C433E7 for ; Fri, 9 Oct 2020 18:41:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6822B222B9 for ; Fri, 9 Oct 2020 18:41:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728317AbgJISlU (ORCPT ); Fri, 9 Oct 2020 14:41:20 -0400 Received: from www62.your-server.de ([213.133.104.62]:47396 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727737AbgJISlU (ORCPT ); Fri, 9 Oct 2020 14:41:20 -0400 Received: from sslproxy06.your-server.de ([78.46.172.3]) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1kQxKP-0006ye-4I; Fri, 09 Oct 2020 20:41:17 +0200 Received: from [178.196.57.75] (helo=pc-9.home) by sslproxy06.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kQxKO-0004fF-VU; Fri, 09 Oct 2020 20:41:17 +0200 Subject: Re: libbpf error: unknown register name 'r0' in asm To: Andrii Nakryiko Cc: Yaniv Agman , bpf , Yonghong Song References: From: Daniel Borkmann Message-ID: Date: Fri, 9 Oct 2020 20:41:16 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.102.4/25952/Fri Oct 9 15:52:40 2020) Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 10/9/20 8:35 PM, Andrii Nakryiko wrote: > On Fri, Oct 9, 2020 at 11:21 AM Daniel Borkmann wrote: >> On 10/9/20 8:09 PM, Yaniv Agman wrote: >>> ‫בתאריך יום ו׳, 9 באוק׳ 2020 ב-20:39 מאת ‪Daniel Borkmann‬‏ >>> <‪daniel@iogearbox.net‬‏>:‬ >>>> >>>> On 10/9/20 6:56 PM, Yaniv Agman wrote: >>>>> ‫בתאריך יום ו׳, 9 באוק׳ 2020 ב-19:27 מאת ‪Daniel Borkmann‬‏ >>>>> <‪daniel@iogearbox.net‬‏>:‬ >>>>>> >>>>>> [ Cc +Yonghong ] >>>>>> >>>>>> On 10/9/20 6:05 PM, Yaniv Agman wrote: >>>>>>> Pulling the latest changes of libbpf and compiling my application with it, >>>>>>> I see the following error: >>>>>>> >>>>>>> ../libbpf/src//root/usr/include/bpf/bpf_helpers.h:99:10: error: >>>>>>> unknown register name 'r0' in asm >>>>>>> : "r0", "r1", "r2", "r3", "r4", "r5"); >>>>>>> >>>>>>> The commit which introduced this change is: >>>>>>> 80c7838600d39891f274e2f7508b95a75e4227c1 >>>>>>> >>>>>>> I'm not sure if I'm doing something wrong (missing include?), or this >>>>>>> is a genuine error >>>>>> >>>>>> Seems like your clang/llvm version might be too old. >>>>> >>>>> I'm using clang 10.0.1 >>>> >>>> Ah, okay, I see. Would this diff do the trick for you? >>> >>> Yes! Now it compiles without any problems! >> >> Great, thx, I'll cook proper fix and check with clang6 as Yonghong mentioned. > > Am I the only one confused here?... Yonghong said it should be > supported as early as clang 6, Yaniv is using Clang 10 and is still > getting this error. Let's figure out what's the problem before adding > unnecessary checks. > > I think it's not the clang_major check that helped, rather __bpf__ > check. So please hold off on the fix, let's get to the bottom of this > first. I don't see confusion here (maybe other than which minimal clang/llvm version libbpf should support). If we do `#if __clang_major__ >= 6 && defined(__bpf__)` for the final patch, then this means that user passed clang -target bpf and the min supported version for inline assembly was there, otherwise we fall back to bpf_tail_call. In Yaniv's case, he probably had native target with -emit-llvm and then used llc invocation. >>>> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h >>>> index 2bdb7d6dbad2..31e356831fcf 100644 >>>> --- a/tools/lib/bpf/bpf_helpers.h >>>> +++ b/tools/lib/bpf/bpf_helpers.h >>>> @@ -72,6 +72,7 @@ >>>> /* >>>> * Helper function to perform a tail call with a constant/immediate map slot. >>>> */ >>>> +#if __clang_major__ >= 10 && defined(__bpf__) >>>> static __always_inline void >>>> bpf_tail_call_static(void *ctx, const void *map, const __u32 slot) >>>> { >>>> @@ -98,6 +99,9 @@ bpf_tail_call_static(void *ctx, const void *map, const __u32 slot) >>>> :: [ctx]"r"(ctx), [map]"r"(map), [slot]"i"(slot) >>>> : "r0", "r1", "r2", "r3", "r4", "r5"); >>>> } >>>> +#else >>>> +# define bpf_tail_call_static bpf_tail_call >>>> +#endif /* __clang_major__ >= 10 && __bpf__ */ >>>> >>>> /* >>>> * Helper structure used by eBPF C program >>