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Date: Wed, 6 Dec 2023 06:59:07 +0900
From: Greg KH <greg@...ah.com>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Al Viro <viro@...iv.linux.org.uk>, tanzirh@...gle.com,
	Kees Cook <keescook@...omium.org>,
	Andy Shevchenko <andy@...nel.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 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:
> > > This diff uses an open source tool include-what-you-use (IWYU) to modify
> > > the include list changing indirect includes to direct includes.
> >
> > How does it account for arch- and config-dependent indirect includes?
> >
> > In particular, on sh this patch breaks, since there word-at-a-time.h does not
> > contain an include of kernel.h, even though it uses REPEAT_BYTE.  This is
> > a very simple case (they really ought to include kernel.h, same as all other
> > instances of word-at-a-time.h), but I would expect arseloads of more subtle
> > breakage in anything less trivial.
> >
> > And I'm not at all sure that there's no config-dependent breakage as well -
> > this had been caught by quick make allmodconfig + make lib/string.o on
> > a bunch of architectures; the graph of indirects includes (as well as the
> > set of symbols needed for given header) is very much config-dependent.
> 
> We're sending these to Kees to stage in branch flowing into linux-next
> in order for the patches to get soak time in linux-next; it's not
> possible to test every possible randconfig, but with enough soak time
> and the bots chewing on linux-next, I think we can get to a certain
> level of confidence.
> 
> We'll ramp up the amount of testing we're doing locally as well. (I
> did quite a few randconfigs locally in a loop; didn't test all
> architectures) We can probably fetch the kernel.org toolchains for
> very extensive testing.
> https://mirrors.edge.kernel.org/pub/tools/crosstool/
> 
> >
> > > 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?

General rule, NEVER include asm/*.h, there should be a include/*.h
instead that works.  So much so that checkpatch.pl should catch this,
right?

But of course, it doesn't always hold true, there are a few minor
exceptions, but they are rare.

thanks,

greg k-h

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