linux-kernel - Re: [PATCH libcrypto 1/2] array_size: introduce min_array

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Message-ID: <aR4UvNzdLLofbRpW@zx2c4.com>
Date: Wed, 19 Nov 2025 20:04:28 +0100
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Ard Biesheuvel <ardb@...nel.org>, Kees Cook <kees@...nel.org>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH libcrypto 1/2] array_size: introduce min_array_size()
 function decoration

On Wed, Nov 19, 2025 at 12:31:11AM +0100, Jason A. Donenfeld wrote:
> There's also this other approach from 2001 that the C committee I guess
> shot down: https://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_205.htm
> It is basically:
> 
>     #define __at_least static
> 
> We could attempt to do the same with `at_least`...
> 
> It kind of feels like we're just inventing a language at that point
> though.

Actually, you know, the more this apparently terrible idea sits in my
head, the more I like it.

Which of these is most readable to you?

bool __must_check xchacha20poly1305_decrypt(
        u8 *dst, const u8 *src, const size_t src_len, const u8 *ad,
        const size_t ad_len, const u8 nonce[min_array_size(XCHACHA20POLY1305_NONCE_SIZE)],
        const u8 key[min_array_size(CHACHA20POLY1305_KEY_SIZE)]);

bool __must_check xchacha20poly1305_decrypt(
        u8 *dst, const u8 *src, const size_t src_len, const u8 *ad,
        const size_t ad_len, const u8 nonce[static XCHACHA20POLY1305_NONCE_SIZE],
        const u8 key[static CHACHA20POLY1305_KEY_SIZE]);

bool __must_check xchacha20poly1305_decrypt(
        u8 *dst, const u8 *src, const size_t src_len, const u8 *ad,
        const size_t ad_len, const u8 nonce[at_least XCHACHA20POLY1305_NONCE_SIZE],
        const u8 key[at_least CHACHA20POLY1305_KEY_SIZE]);

The macro function syntax of the first one means nested bracket brain
parsing. The second one means more `static` usage that might be
unfamiliar. The third one actually makes it kind of clear what's up.
It's got that weird-but-nice Objective-C-style sentence programming
thing.

Would somebody jump in here to tell me to stop sniffing glue? I feel
silly actually considering this, but here I am. Maybe this is actually
an okay idea?

Jason