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

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Date: Tue, 5 Dec 2023 13:51:10 -0800
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: 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 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?

>
> > 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.
-- 
Thanks,
~Nick Desaulniers