linux-kernel - Re: Q: crypto/cipher.c

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Message-ID: <49ECC1DF.3040401@grupopie.com>
Date:	Mon, 20 Apr 2009 19:41:35 +0100
From:	Paulo Marques <pmarques@...popie.com>
To:	H Hartley Sweeten <hartleys@...ionengravers.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Q: crypto/cipher.c

H Hartley Sweeten wrote:
> Hello all,

Hi,

> I have a question about the following code in crypto/cipher.c.
> 
> static void cipher_crypt_unaligned(void (*fn)(struct crypto_tfm *, u8 *,
> 					      const u8 *),
> 				   struct crypto_tfm *tfm,
> 				   u8 *dst, const u8 *src)
> {
> 	unsigned long alignmask = crypto_tfm_alg_alignmask(tfm);
> 	unsigned int size = crypto_tfm_alg_blocksize(tfm);
> 	u8 buffer[size + alignmask];
> 	u8 *tmp = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
> 
> 	memcpy(tmp, src, size);
> 	fn(tfm, tmp, tmp);
> 	memcpy(dst, tmp, size);
> }
> 
> Doesn't the size of buffer need to be known at compile time for this
> to actually work? Or do alignmask and size work out to be constants?
> 
> This appears to be buggy. But I may just be missing something...

It's a GCC extension:

http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html

-- 
Paulo Marques - www.grupopie.com

"All generalizations are false."
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