Re: [PATCH 00/14] perf clang: Support compiling BPF script use builtin clang

[Wangnan (F)]

On 2016/9/27 7:58, Arnaldo Carvalho de Melo wrote:
> Le 26 sept. 2016 8:47 PM, "Alexei Starovoitov" 
> <alexei.starovoitov@xxxxxxxxx <mailto:alexei.starovoitov@xxxxxxxxx>> a 
> Ãcrit :
> >
> > On Mon, Sep 26, 2016 at 09:49:30AM +0800, Wangnan (F) wrote:
> > >
> > >
> > > On 2016/9/24 23:16, Alexei Starovoitov wrote:
> > > >On Fri, Sep 23, 2016 at 12:49:47PM +0000, Wang Nan wrote:
> > > >>This patch set is the first step to implement features I announced
> > > >>in LinuxCon NA 2016. See page 31 of:
> > > >>
> > > >> 
> http://events.linuxfoundation.org/sites/events/files/slides/Performance%20Monitoring%20and%20Analysis%20Using%20perf%20and%20BPF_1.pdf
> > > >>
> > > >>This patch set links LLVM and Clang libraries to perf, so perf
> > > >>is able to compile BPF script to BPF object on the fly.
> > > >Nice!
> > > >So single perf binary won't have llvm external dependency anymore
> > > >or both ways will be maintained?
> > > >The command line stays the same?
> > >
> > > Yes. This patch set doesn't change interface. It compiles BPF script
> > > with builtin clang, and if it fail, fall back to external clang.
> > >
> > > >If I understand the patches correctly, this set is establishing
> > > >the basic functionality and more complex features coming?
> > > >
> > >
> > > Yes. Following steps are:
> > >
> > >  1. Ease of use improvement: automatically include BPF functions
> > >     declaration and macros.
> >
> > +1
> >
> > >  2. Perf's hook: compile part of BPF script into native code, run
> > >     them in perf when something happen. Create a channel, coordinate
> > >     BPF and native code use bpf-output event.
> >
> > +1
> >
> > >  3. Define a new language to support common profiling task. I'm not
> > >     very clear what the new language should be. It may looks like lua,
> > >     perf converts it to C then to LLVM IR with builtin clang.
> >
> > Many tracing languages were invented in the past.
> > At this point I'm not sure what exactly new language will solve.
> > To make it easier to write bpf programs?
> > I think it will be more fruitful to tweak clang/llvm to add
> > good warnings/errors for cases where we know that C is not going
> > be compiled into the code that the kernel verifier will accept.
> > Like we can complain about loops, unitialized variables,
> > non-inlined and unkown helper functions... all from clang/llvm.
> > imo that would be the better path forward and will help
> > both tracing and networking users that write in this restricted C.
>
> ++1
> >

OK. Now let's focus on the first two goals. After that let's consider
how to help writing BPF program.

Thank you.