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Date:   Thu, 6 Jun 2019 13:54:06 -0700
From:   Tom Roeder <tmroeder@google.com>
To:     Raul E Rangel <rrangel@chromium.org>
Cc:     yamada.masahiro@socionext.com, mka@chromium.org,
        ndesaulniers@google.com, zwisler@chromium.org,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        linux-kbuild@vger.kernel.org, Petr Mladek <pmladek@suse.com>,
        linux-kernel@vger.kernel.org,
        Michal Marek <michal.lkml@markovi.net>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Changbin Du <changbin.du@intel.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Sri Krishna chowdary <schowdary@nvidia.com>,
        Matthew Wilcox <willy@infradead.org>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH] kbuild: Add option to generate a Compilation Database
Message-ID: <20190606205406.GA120512@google.com>
References: <20190606203003.112040-1-rrangel@chromium.org>
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On Thu, Jun 06, 2019 at 02:30:03PM -0600, Raul E Rangel wrote:
> Clang tooling requires a compilation database to figure out the build
> options for each file. This enables tools like clang-tidy and
> clang-check.
> 
> See https://clang.llvm.org/docs/HowToSetupToolingForLLVM.html for more
> information.

I'm glad to see someone adding this to the Makefile directly. I added
scripts/gen_compile_commands.py in b302046 (in Dec 2018) when I was
working on using clang-check to look for bugs in KVM. That script
sidesteps the -MJ option because I found that trying to add it as an
extra option ended up adding entries to the database that didn't work
properly in some cases. This patch adds -MJ in a different way than I
was trying, so I hope it doesn't have the same problems.

I would much prefer to have this functionality integrated into the
Makefile system directly, so if this works with clang-check over all
files and doesn't lead to spurious entries in the database, I'm all for
it.

> 
> Normally cmake is used to generate the compilation database, but the
> linux kernel uses make. Another option is using
> [BEAR](https://github.com/rizsotto/Bear) which instruments
> exec to find clang invocations and generate the database that way.
> 
> Clang 4.0.0 added the -MJ option to generate the json for each
> compilation unit. https://reviews.llvm.org/D27140
> 
> This patch takes advantage of the -MJ option. So it only works for
> Clang.
> 
Can you please add details about how this was tested and compare
coverage with the existing script?

Tom