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charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Oct 9, 2020 at 11:41 AM Daniel Borkmann wrot= e: > > 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 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 men= tioned. > > > > 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 ver= sion > libbpf should support). If we do `#if __clang_major__ >=3D 6 && defined(_= _bpf__)` > for the final patch, then this means that user passed clang -target bpf a= nd > the min supported version for inline assembly was there, otherwise we fal= l back > to bpf_tail_call. In Yaniv's case, he probably had native target with -em= it-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. > > >>>> 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/immedi= ate map slot. > >>>> */ > >>>> +#if __clang_major__ >=3D 10 && defined(__bpf__) > >>>> static __always_inline void > >>>> bpf_tail_call_static(void *ctx, const void *map, const __u32 slo= t) > >>>> { > >>>> @@ -98,6 +99,9 @@ bpf_tail_call_static(void *ctx, const void *map, c= onst __u32 slot) > >>>> :: [ctx]"r"(ctx), [map]"r"(map), [slot]"i"(sl= ot) > >>>> : "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 > >> >