Re: [PATCH 1/3] tools: fix off-by 1 relative directory includes

From: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
To: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Igor Lubashev <ilubashe@akamai.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Alexios Zavras <alexios.zavras@intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Wei Li <liwei391@huawei.com>,
	Kan Liang <kan.liang@linux.intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH 1/3] tools: fix off-by 1 relative directory includes
Date: Fri, 6 Mar 2020 17:13:31 -0300	[thread overview]
Message-ID: <20200306201331.GC13774@kernel.org> (raw)
In-Reply-To: <CAP-5=fUAjMxGDWfev_q6vKhe1M5D1UdXhPK6x5Y9bxUbrJ-tNw@mail.gmail.com>

Em Fri, Mar 06, 2020 at 08:47:51AM -0800, Ian Rogers escreveu:
> On Fri, Mar 6, 2020 at 1:34 AM Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > On Thu, Mar 05, 2020 at 11:11:08PM -0800, Ian Rogers wrote:
> > > This is currently working due to extra include paths in the build.
> >
> > if you're fixing this, why not remove that extra include path then?
> 
> TL;DR it is complicated, but the include paths are all currently
> necessary I believe and doing this way is necessary due to how header
> files may be copied out of the kernel.

TL;DR response: yeah, lets make incremental fixes to this, like applying
this patch :)

- Arnaldo
 
> The current build uses multiple -Is to ensure the correct version of a
> file is included, for example there are 27 files called bitops.h and
> 29 called bitsperlong.h. In
> Google we're using libraries and bazel build files:
> https://docs.bazel.build/versions/master/be/c-cpp.html#cc_library
> and there's no way to say if you depend on this library then you need
> this include path. We've tried to make perf this way but having tied
> ourselves in knots we decided instead to emulate the include path
> behaviour by rewriting includes when we import code using copybara:
> https://github.com/google/copybara
> We are able when doing this to prioritize the include paths we rewrite
> so that a local directory version of a header is preferred over say
> one in tools/lib/perf and perhaps tools/perf. Having full include
> paths isn't really an option upstream as the same header file may be
> copied into a libc project that has a different directory layout.
> As we have absolute include paths at the time of building we need
> relative include paths to be correct. Upstream -Is allow the build to
> find the file but it is a bit of a quirk of the C preprocessor, so
> fixing these off-by 1s feels like value add both for us and upstream.
> For upstream to do anything different I think is going to be a
> significant rewrite of how the Makefile build works and I'm not sure
> what the result would look like.
> 
> Thanks!
> Ian
> 
> > jirka
> >

-- 

- Arnaldo