From: Yonghong Song <firstname.lastname@example.org> To: Matthias Kaehlcke <email@example.com>, Josh Poimboeuf <firstname.lastname@example.org> Cc: Arnaldo Carvalho de Melo <email@example.com>, Daniel Borkmann <firstname.lastname@example.org>, Wang Nan <email@example.com>, Alexei Starovoitov <firstname.lastname@example.org>, Adrian Hunter <email@example.com>, David Ahern <firstname.lastname@example.org>, Jiri Olsa <email@example.com>, Ingo Molnar <firstname.lastname@example.org>, Namhyung Kim <email@example.com>, Linux Kernel Mailing List <firstname.lastname@example.org>, Andrey Ryabinin <email@example.com> Subject: Re: perf test LLVM & clang 6 failing Date: Mon, 27 Nov 2017 17:19:17 -0800 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <20171127214521.GB53228@google.com> On 11/27/17 1:45 PM, Matthias Kaehlcke wrote: > El Mon, Nov 27, 2017 at 01:57:56PM -0600 Josh Poimboeuf ha dit: > >> On Mon, Nov 27, 2017 at 04:34:25PM -0300, Arnaldo Carvalho de Melo wrote: >>> Em Mon, Nov 27, 2017 at 11:11:56AM -0800, Yonghong Song escreveu: >>>> On 11/27/17 9:04 AM, Arnaldo Carvalho de Melo wrote: >>>>> Em Fri, Nov 24, 2017 at 04:16:52PM +0100, Daniel Borkmann escreveu: >>>>>> [ +Yonghong ] >>>>> >>>>> + Josh >>>>>> On 11/24/2017 03:47 PM, Arnaldo Carvalho de Melo wrote: >>>>>>> FYI, just noticed, recently updated clang to version 6, from its >>>>>>> upstream git repo. >>>>>> >>>>>> Do you recall what was your LLVM version prior to this where it was >>>>>> working fine? (Wild guess from below would be the BPF inline asm >>>>>> support that was added recently to LLVM (2865ab6996) vs asm() used >>>>>> in headers included in the stdin header causing trouble due to arch >>>>>> mixup?) >>>>> >>>>> So, if I go to the cset just before: >>>>> >>>>> commit f5caf621ee357279e759c0911daf6d55c7d36f03 >>>>> Author: Josh Poimboeuf <email@example.com> >>>>> Date: Wed Sep 20 16:24:33 2017 -0500 >>>>> >>>>> x86/asm: Fix inline asm call constraints for Clang >>>>> --- >>>>> >>>>> 'perf test LLVM' works again: >>>>> >>>>> [root@jouet ~]# perf test LLVM >>>>> 37: LLVM search and compile : >>>>> 37.1: Basic BPF llvm compile : Ok >>>>> 37.2: kbuild searching : Ok >>>>> 37.3: Compile source for BPF prologue generation : Ok >>>>> 37.4: Compile source for BPF relocation : Ok >>>>> [root@jouet ~]# >>>>> >>>>> I.e. 'perf test LLVM' built from what is in my acme/perf/urgent branch, >>>>> targetted to v4.15, uses kernel headers and if I go to just before >>>>> f5caf621ee, it works again, both with clang from fedora26 (4.0.1) and >>>>> with 6.0, built from sources. >>>> >>>> This patch introduced a module level inline assembly. >>>> >>>> ... >>>> --- a/arch/x86/include/asm/asm.h >>>> +++ b/arch/x86/include/asm/asm.h >>>> @@ -132,4 +132,15 @@ >>>> /* For C file, we already have NOKPROBE_SYMBOL macro */ >>>> #endif >>>> >>>> +#ifndef __ASSEMBLY__ >>>> +/* >>>> + * This output constraint should be used for any inline asm which has a >>>> "call" >>>> + * instruction. Otherwise the asm may be inserted before the frame pointer >>>> + * gets set up by the containing function. If you forget to do this, >>>> objtool >>>> + * may print a "call without frame pointer save/setup" warning. >>>> + */ >>>> +register unsigned int __asm_call_sp asm("esp"); >>>> +#define ASM_CALL_CONSTRAINT "+r" (__asm_call_sp) >>>> +#endif >>>> ... >>>> >>>> This will cause "clang ... -target bpf ..." failure since 4.0 does not have >>>> bpf inline asm support and 6.0 does not recognize the register 'esp'. >>> >>> Ok, explains the problem then, Josh, ideas on how to proceed here? >> >> The original change to add the global inline asm: >> >> 5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang") >> >> was done to support clang in the first place. Before that change, a >> clang-built kernel didn't even boot. So I'm a bit perplexed by the fact >> that this change would be causing clang problems, since it was done to >> fix clang in the first place. >> >> Adding Andrey and Matthias, maybe they can help clarify things. > > Indeed the change was needed to boot on x86. > > I know next to nothing about BPF, if I understand correctly the error > is generated when compiling for the BPF "architecture" not for x86. In > this process x86 assembly headers are included, one of which contains > the declaration of the register variable, in an register that exists > on x86, but not BPS. > > I guess the first questions is whether the x86 asm headers should/need > to be included when compiling for BPF. If this needed/can not be > easily avoided one option could be to put the declaration within an > ifdef __x86_64__ block. There is a way to do this. You can use the similar mechanism to the one in linux:samples/bpf and linux:tools/testing/selftests/bpf. Basically, you first do: clang ... -O2 -emit-llvm -S prog.c <=== this uses x86_64 as the default target llc -march=bpf -filetype=obj prog.ll <=== this uses bpf target This should work.
next prev parent reply other threads:[~2017-11-28 1:20 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-11-24 14:47 Arnaldo Carvalho de Melo 2017-11-24 15:16 ` Daniel Borkmann 2017-11-24 19:09 ` Arnaldo Carvalho de Melo 2017-11-26 6:29 ` Yonghong Song 2017-11-27 17:04 ` Arnaldo Carvalho de Melo 2017-11-27 19:11 ` Yonghong Song 2017-11-27 19:34 ` Arnaldo Carvalho de Melo 2017-11-27 19:57 ` Josh Poimboeuf 2017-11-27 21:45 ` Matthias Kaehlcke 2017-11-28 1:19 ` Yonghong Song [this message] 2017-11-28 17:55 ` Arnaldo Carvalho de Melo 2017-11-28 17:59 ` Arnaldo Carvalho de Melo 2017-12-06 16:44 ` [tip:perf/core] x86/asm: Allow again using asm.h when building for the 'bpf' clang target tip-bot for Arnaldo Carvalho de Melo 2017-12-18 17:17 ` [tip:perf/urgent] " tip-bot for Arnaldo Carvalho de Melo 2017-11-27 20:05 ` perf test LLVM & clang 6 failing Arnaldo Carvalho de Melo
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