linux-kernel - Re: [GIT PULL 0/6] perf/core improvements and fixes

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Date:	Thu, 04 Jun 2015 09:22:23 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Ingo Molnar <mingo@...nel.org>, pi3orama <pi3orama@....com>
CC:	"Wangnan (F)" <wangnan0@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	David Ahern <dsahern@...il.com>, He Kuang <hekuang@...wei.com>,
	Jiri Olsa <jolsa@...hat.com>, Kaixu Xia <xiakaixu@...wei.com>,
	Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Zefan Li <lizefan@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [GIT PULL 0/6] perf/core improvements and fixes

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]'

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