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

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

On 2015/06/05 1:22, Alexei Starovoitov wrote:
> 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]'

I think we'd better make 'perf record -e file.c' default and '-e file.o'
should be an option.

Thank you,

> 
> 


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@hitachi.com