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Date: Tue, 5 Dec 2023 13:51:10 -0800
From: Nick Desaulniers <>
To: Al Viro <>
Cc:, Kees Cook <>, 
	Andy Shevchenko <>,,, Nick DeSaulniers <>, 
	Andrew Morton <>,
Subject: Re: [PATCH] lib/string: shrink lib/string.i via IWYU

On Tue, Dec 5, 2023 at 1:38 PM Al Viro <> wrote:
> On Tue, Dec 05, 2023 at 08:58:53PM +0000, 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 toolchains for
very extensive testing.

> > 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?

> > If there are any problems with the output of the tool please raise an
> > issue on the github.
> Sorry, no.  Your tool, your workflow, of course, but I don't do github issues.
> You are welcome to the contents of this reply, but I'm not using browser-based
> UI without very strong reasons; this one isn't.

No problem; Tanzir, please drop that part of the commit message in
future patches.
~Nick Desaulniers

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