linux-kernel - Re: [PATCH v3 10/30] perf clang: Add builtin clang support ant test case

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Date:   Tue, 6 Dec 2016 10:43:29 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Wangnan (F)" <wangnan0@...wei.com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>, ast@...com,
        lizefan@...wei.com, hekuang@...wei.com,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        pi3orama@....com, joe@....org, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v3 10/30] perf clang: Add builtin clang support ant test
 case

Em Tue, Dec 06, 2016 at 10:07:51AM +0800, Wangnan (F) escreveu:
> On 2016/12/6 5:48, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Dec 05, 2016 at 07:02:48PM -0200, Arnaldo Carvalho de Melo escreveu:
> > > Em Mon, Dec 05, 2016 at 08:51:01AM -0800, Alexei Starovoitov escreveu:
> > > > yeah. it's kinda high. I'm guessing rpm llvm libs are in debug mode.
> > > > Try llvm-config --build-mode --assertion-mode
> > > > it should be Release OFF
> > > Probably this was with 3.9 and built from git, quite a while ago, now I
> > > removed it from /usr/local/ and installed what is in f25, but I fear it
> > > will be insufficient, does 3.8 cuts it for what we're testing? Humm, it
> > > looks like it will:

> > > [root@...et ~]# llc --version
> > > LLVM (http://llvm.org/):
> > >    LLVM version 3.8.0

> > > But I'm now running the container based tests to send a pull req, will
> > > check later, after that.
> > Not really, Wang, we need to update that feature detection test to state what
> > is the minimum required LLVM/clang version, one that has those functions,
> > which, unfortunately, isn't the one in the latest fedora, fedora 25:
 
> I'll set the minimum required LLVM version to 3.9, and report
> warning when LLVM is too old. However, since LLVM interface is
> keep changing, finally we will have problem if we want to support
> 2 or 3 different clang/LLVM. We should keep moving minimum
> requirement LLVM version if we don't want to see '#ifdef's
> spread in our code.

If this area is in that much flux, I see no problem in us both not
enabling this by default, which is the case right now, and go on moving
the minimum required version for LLVM/clang, hopefully at some point
this will get stable and widely available (as in what distros ship),
when we then switch to doing the feature detection automatically.

I see you already submitted the patch to do this test, thanks, will
check and continue processing your series.

- Arnaldo