linux-kernel - Re: [PATCH] lib/string: shrink lib/string.i via IWYU

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Date:   Thu, 7 Dec 2023 14:52:40 +0200
From:   Andy Shevchenko <andy@...nel.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>, tanzirh@...gle.com,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nick DeSaulniers <nnn@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH] lib/string: shrink lib/string.i via IWYU

On Tue, Dec 05, 2023 at 10:15:21PM +0000, Al Viro wrote:
> On Wed, Dec 06, 2023 at 12:01:56AM +0200, Andy Shevchenko wrote:
> > On Tue, Dec 05, 2023 at 01:51:10PM -0800, Nick Desaulniers wrote:
> > > On Tue, Dec 5, 2023 at 1:38 PM Al Viro <viro@...iv.linux.org.uk> wrote:
> > > > On Tue, Dec 05, 2023 at 08:58:53PM +0000, tanzirh@...gle.com wrote:

...

> > > > > IWYU is implemented using the IWYUScripts github repository which is a tool that is
> > > > > currently undergoing development. These changes seek to improve build times.
> > > > >
> > > > > This change to lib/string.c resulted in a preprocessed size of
> > > > > lib/string.i from 26371 lines to 5232 lines (-80%).
> > > >
> > > > It also breeds includes of asm/*.h, by the look of the output, which is
> > > > not a good thing in general ;-/  E.g. #include <asm/uaccess.h> *anywhere*
> > > > outside of linux/uaccess.h is a bad idea.
> > > 
> > > It's not clear to me when it's ok to #include <asm/*.h>.  Is there a
> > > convention here that I'm missing?
> > 
> > The mandatory ones can be used, but not all of them.
> > In some cases you even must include asm and not linux
> > (unaligned.h, byteorder.h, maybe others...).
> > 
> > As I told, it comes with experience, we lack of the
> > respective documentation (or file which is good for
> > automation checks, like with IWYU).
> 
> It would certainly be nice to have such information in the tree;
> "where should I pick $SYMBOL from?" is something one needs to
> find out often enough.  To a large extent it's covered by "where
> in include/*.h do we have it defined?", but that's not all there
> is to it.  E.g. "get_user() => use linux/uaccess.h".
> 
> There's also stuff like "$SYMBOL should not be used outside of arch/*
> and include/*, better use $OTHER_SYMBOL", etc.

Precisely! That's what many developers will benefit from!

-- 
With Best Regards,
Andy Shevchenko