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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=Aaix22CaWnRDu3/8LriA9DlXQfNq4WOB0b0IHGrXbsk=; b=TNw/q6RMey38PgU2ACjYVyN3dH8oyQ8O8q5z670hs4ueIvlF9rd5VwEH2ERhHChCEs PHURtlH+M22GQeg3BVEGn9lGdUGvbpLKIegVBeI6yOkNreUjbagZrwEnR1AX1FiYXXaf MA6IHbpW/TFH2kL7zbFw4rVh7WbUAuvDMRrXMoDOBZnhSjcofp1xNKQ0o+QL3FyMdvrC h24sAgdX37IfsO9c3dwQA0cbzEfhGfVN6SS4vYLN/8NjGqDsgtnp5AXjnUHW+Ul0XGCd d6W8VuQgviqV7p4LmfDHot+hPDqvZDz8rr11KQkipi58Nerlth73kBk45Z8KUlcUVC/Y 8G+Q== X-Gm-Message-State: AOAM530MG/lIAKbZfLNLuVMfC21lcacmt/rQgGe+PmoP7+MPVQbmfza8 j88XgKaOhMh/ekVsl1EEHSfWfV8SknC/GTBkhkg= X-Google-Smtp-Source: ABdhPJyiXONWzElDjMyqp9Ms7jp5oMTTnHabEGy5BBg71I7HBHpASY/gy4fq0koJAQ521Eh64Dl0UHPA58jaAlRCbRQ= X-Received: by 2002:a05:6402:b31:: with SMTP id bo17mr856228edb.342.1602272048220; Fri, 09 Oct 2020 12:34:08 -0700 (PDT) MIME-Version: 1.0 References: <231e3e6b-0118-f600-05c5-f4e2f2c76129@fb.com> In-Reply-To: <231e3e6b-0118-f600-05c5-f4e2f2c76129@fb.com> From: Yaniv Agman Date: Fri, 9 Oct 2020 22:33:56 +0300 Message-ID: Subject: Re: libbpf error: unknown register name 'r0' in asm To: Yonghong Song Cc: Andrii Nakryiko , Daniel Borkmann , bpf Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org =E2=80=AB=D7=91=D7=AA=D7=90=D7=A8=D7=99=D7=9A =D7=99=D7=95=D7=9D =D7=95=D7= =B3, 9 =D7=91=D7=90=D7=95=D7=A7=D7=B3 2020 =D7=91-22:08 =D7=9E=D7=90=D7=AA = =E2=80=AAYonghong Song=E2=80=AC=E2=80=8F <=E2=80=AAyhs@fb.com=E2=80=AC=E2= =80=8F>:=E2=80=AC > > > > On 10/9/20 11:59 AM, Andrii Nakryiko wrote: > > On Fri, Oct 9, 2020 at 11:41 AM Daniel Borkmann = wrote: > >> > >> 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: > >>>>> =E2=80=AB=D7=91=D7=AA=D7=90=D7=A8=D7=99=D7=9A =D7=99=D7=95=D7=9D = =D7=95=D7=B3, 9 =D7=91=D7=90=D7=95=D7=A7=D7=B3 2020 =D7=91-20:39 =D7=9E=D7= =90=D7=AA =E2=80=AADaniel Borkmann=E2=80=AC=E2=80=8F > >>>>> <=E2=80=AAdaniel@iogearbox.net=E2=80=AC=E2=80=8F>:=E2=80=AC > >>>>>> > >>>>>> On 10/9/20 6:56 PM, Yaniv Agman wrote: > >>>>>>> =E2=80=AB=D7=91=D7=AA=D7=90=D7=A8=D7=99=D7=9A =D7=99=D7=95=D7=9D = =D7=95=D7=B3, 9 =D7=91=D7=90=D7=95=D7=A7=D7=B3 2020 =D7=91-19:27 =D7=9E=D7= =90=D7=AA =E2=80=AADaniel Borkmann=E2=80=AC=E2=80=8F > >>>>>>> <=E2=80=AAdaniel@iogearbox.net=E2=80=AC=E2=80=8F>:=E2=80=AC > >>>>>>>> > >>>>>>>> [ Cc +Yonghong ] > >>>>>>>> > >>>>>>>> On 10/9/20 6:05 PM, Yaniv Agman wrote: > >>>>>>>>> Pulling the latest changes of libbpf and compiling my applicati= on 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?), o= r 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 m= entioned. > >>> > >>> 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__ >=3D 6 && define= d(__bpf__)` > >> for the final patch, then this means that user passed clang -target bp= f 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. > > > > The "-emit-llvm" was the part that we were missing and had to figure > > it out, before we could discuss the fix. > > Maybe Yaniv can confirm. I think the following properly happens. > - clang10 -O2 -g -S -emit-llvm t.c // This is native compilation > becasue some header files. Maybe some thing is guarded with x86 specific > config's which is not available to -target bpf. This is mostly for > tracing programs and Yanic mentions pt_regs which should be related > to tracing. > - llc -march=3Dbpf t.ll > Yes, like I said, I do use --emit-llvm, and indeed have a tracing program > So guarding the function with __bpf__ should be the one fixing this issue= . > > guard with clang version >=3D6 should not hurt and may prevent > compilation failures if people use < 6 llvm with clang -target bpf. > I think most people should already use newer llvm, but who knows. > > > > >> > >>>>>> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpe= rs.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/imm= ediate map slot. > >>>>>> */ > >>>>>> +#if __clang_major__ >=3D 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 > > > > bpf_tail_call_static has very specific guarantees, so in cases where > > we can't use inline assembly to satisfy those guarantees, I think we > > should not just silently redefine bpf_tail_call_static as > > bpf_tail_call, rather make compilation fail if someone is attempting > > to use bpf_tail_call_static. _Static_assert could be used to provide a > > better error message here, probably. > > > >>>>>> +#endif /* __clang_major__ >=3D 10 && __bpf__ */ > >>>>>> > >>>>>> /* > >>>>>> * Helper structure used by eBPF C program > >>>> > >>