linux-kernel - Re: [PATCH 1/1] tools build: Fix llvm feature detection, still used by bpftool

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Date:   Thu, 19 Oct 2023 23:50:20 +0100
From:   Quentin Monnet <quentin@...valent.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Manu Bretelle <chantr4@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Carsten Haitzler <carsten.haitzler@....com>,
        Eduard Zingerman <eddyz87@...il.com>,
        Fangrui Song <maskray@...gle.com>,
        He Kuang <hekuang@...wei.com>, Ian Rogers <irogers@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        James Clark <james.clark@....com>,
        Jiri Olsa <jolsa@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Leo Yan <leo.yan@...aro.org>, llvm@...ts.linux.dev,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Rob Herring <robh@...nel.org>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Tom Rix <trix@...hat.com>, Wang Nan <wangnan0@...wei.com>,
        Wang ShaoBo <bobo.shaobowang@...wei.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        Yonghong Song <yhs@...com>, YueHaibing <yuehaibing@...wei.com>,
        linux-perf-users@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH 1/1] tools build: Fix llvm feature detection, still used
 by bpftool

On 19/10/2023 23:47, Andrii Nakryiko wrote:
> On Thu, Oct 19, 2023 at 2:17 PM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
>>
>> When removing the BPF event for perf a feature test that checks if the
>> llvm devel files are availabe was removed but that is also used by
>> bpftool.
>>
>> bpftool uses it to decide what kind of disassembly it will use: llvm or
>> binutils based.
>>
>> Removing the tools/build/feature/test-llvm.cpp file made bpftool to
>> always fallback to binutils disassembly, even with the llvm devel files
>> installed, fix it by restoring just that small test-llvm.cpp test file.
>>
>> Fixes: 56b11a2126bf2f42 ("perf bpf: Remove support for embedding clang for compiling BPF events (-e foo.c)")
> 
> Should we route this through the bpf-next tree to get the fix for
> bpftool into Github mirror ASAP?

It shouldn't be necessary. The GitHub mirror for bpftool uses its own
feature detection mechanism, and is not affected here. This patch won't
even make it to the mirror.

Quentin