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

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Message-ID: <20231205213807.GE1674809@ZenIV>
Date:   Tue, 5 Dec 2023 21:38:07 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     tanzirh@...gle.com
Cc:     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 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.

> 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.

> 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.