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Date:   Tue, 1 Mar 2022 10:14:07 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
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Subject: Re: [PATCH 2/6] treewide: remove using list iterator after loop body
 as a ptr
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On Mon, Feb 28, 2022 at 04:45:11PM -0800, Linus Torvalds wrote:
> Really. The "-Wshadow doesn't work on the kernel" is not some new
> issue, because you have to do completely insane things to the source
> code to enable it.

The first big glitch with -Wshadow was with shadowed global variables.
GCC 4.8 fixed that, but it still yells about shadowed functions. What
_almost_ works is -Wshadow=local. At first glace, all the warnings
look solvable, but then one will eventually discover __wait_event()
and associated macros that mix when and how deeply it intentionally
shadows variables. :)

Another way to try to catch misused shadow variables is
-Wunused-but-set-varible, but it, too, has tons of false positives.

I tried to capture some of the rationale and research here:
https://github.com/KSPP/linux/issues/152

-- 
Kees Cook