linux-kernel - Re: [GIT PULL] string fixes for v6.15-rc1

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Message-ID: <FFE5FB0B-CC92-4A25-8014-E7548AD1C469@kernel.org>
Date: Sun, 06 Apr 2025 18:32:58 -0700
From: Kees Cook <kees@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
CC: linux-kernel@...r.kernel.org, Andrey Konovalov <andreyknvl@...il.com>,
 Andy Shevchenko <andy@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
 Nathan Chancellor <nathan@...nel.org>, Peter Collingbourne <pcc@...gle.com>,
 Vincenzo Frascino <vincenzo.frascino@....com>, Will Deacon <will@...nel.org>
Subject: Re: [GIT PULL] string fixes for v6.15-rc1



On April 6, 2025 12:04:04 PM PDT, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>On Sun, 6 Apr 2025 at 10:54, Kees Cook <kees@...nel.org> wrote:
>>
>> - Add wcslen() to support more Clang libcalls (Nathan Chancellor)
>
>Oh Christ.
>
>Does clang not know how expensive function calls can be?
>
>I really think the right fix here would have been to say "don't do
>that", rather than make that function available.

I should have said "libcall optimizations". It's not just blindly constructing calls. This is the same kind of thing that has been heavily discussed before for bcmp() and stpcpy(). The resolution from those threads was to add the symbol, as the least of many bad options:
https://lore.kernel.org/all/CAK7LNAQHj-GeqH_5WpKo7gA6qZAiX8OOxxnL1v-SNZwRHFSXQQ@mail.gmail.com/


-- 
Kees Cook