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Date: Thu, 04 Jun 2015 09:22:23 -0700
From: Alexei Starovoitov <ast@plumgrid.com>
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To: Ingo Molnar <mingo@kernel.org>, pi3orama <pi3orama@163.com>
CC: "Wangnan (F)" <wangnan0@huawei.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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        Brendan Gregg <brendan.d.gregg@gmail.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        David Ahern <dsahern@gmail.com>, He Kuang <hekuang@huawei.com>,
        Jiri Olsa <jolsa@redhat.com>, Kaixu Xia <xiakaixu@huawei.com>,
        Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Namhyung Kim <namhyung@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
        Zefan Li <lizefan@huawei.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>
Subject: Re: [GIT PULL 0/6] perf/core improvements and fixes
References: <1433371238-14572-1-git-send-email-acme@kernel.org> <20150604054854.GA10969@gmail.com> <556FEB32.8040909@huawei.com> <20150604072153.GA18983@gmail.com> <557021D3.7070900@huawei.com> <20150604124033.GA10580@gmail.com> <0108CD89-BFFA-4A68-90AE-A34597777641@163.com> <20150604140412.GB14445@gmail.com>
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On 6/4/15 7:04 AM, Ingo Molnar wrote:
>> >  # perf record -e bpf_source.c cmdline
>> >
>> >  to create a eBPF filter from source,
>> >
>> >Use
>> >
>> ># perf record -e bpf_object.o cmdline
>> >
>> >to create a eBPF filter from object intermedia.
>> >
>> >Use
>> >
>> ># perf bpf compile bpf_source.c --kbuild=kernel-build-dir -o bpf_object.o
>> >
>> >to create the .o
>> >
>> >I think this should be enough. Currently only the second case has been implemented.
> So if users cannot actually generate .o files then it's premature to merge this in
> such an incomplete form!
>
> It should be possible to use a feature that we are merging.

of course it's usable :) There is some confusion here.
To compile .c into .o one can easily use
clang -O2 -emit-llvm -c file.c -o - | llc -march=bpf -o file.o
any version of clang is ok,
llc needs to be fresh with bpf backend.

For a lot of cases kernel headers are not needed, so above
will work fine.
For our TC examples we recommend to use 'bcc' alias:
bcc() {
   clang -O2 -emit-llvm -c $1 -o - | llc -march=bpf -filetype=obj -o 
"`basename $1 .c`.o"
}
then compiling as easy as 'bcc file.c'

What Wang mentioned that we're working on is fully integrated 'bcc'.
It will use clang/llvm as libraries, so no intermediate steps will
be needed, but some folks will always have concerns about
ultra-embedded environments where even 20Mb of libllvm.so is too much.

So I think we need to support both 'perf record -e file.[co]'