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

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Message-ID: <20200306201331.GC13774@kernel.org>
Date:   Fri, 6 Mar 2020 17:13:31 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Igor Lubashev <ilubashe@...mai.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Alexios Zavras <alexios.zavras@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wei Li <liwei391@...wei.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/3] tools: fix off-by 1 relative directory includes

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@...hat.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