linux-kernel - Re: [PATCH v2] crypto, dm: LLVMLinux: Remove VLAIS usage from dm-crypt

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Date:	Sat, 06 Sep 2014 19:10:06 -0700
From:	Behan Webster <behanw@...verseincode.com>
To:	Milan Broz <gmazyland@...il.com>, agk@...hat.com,
	dm-devel@...hat.com, snitzer@...hat.com
CC:	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	neilb@...e.de, torvalds@...ux-foundation.org,
	Jan-Simon Möller 
	<dl9pf@....de>, pageexec@...email.hu
Subject: Re: [PATCH v2] crypto, dm: LLVMLinux: Remove VLAIS usage from dm-crypt

On 09/06/14 01:46, Milan Broz wrote:
> On 09/06/2014 01:02 AM, behanw@...verseincode.com wrote:
>> From: Jan-Simon Möller <dl9pf@....de>
>>
>> The use of variable length arrays in structs (VLAIS) in the Linux Kernel code
>> precludes the use of compilers which don't implement VLAIS (for instance the
>> Clang compiler). This patch instead allocates the appropriate amount of memory
>> using an char array.
> Well, if clang (or C99 code) is now preferred for kernel, why not.
>
> Just please commit the patch series en bloc (together with the patches
> removing VLAIS from crypto code you posted to cryptoapi list).
They seemed more separate than that. However, happy to post them as a 
patch set.

>> -	struct {
>> -		struct shash_desc desc;
>> -		char ctx[crypto_shash_descsize(lmk->hash_tfm)];
>> -	} sdesc;
>> +	char sdesc[sizeof(struct shash_desc) +
>> +		crypto_shash_descsize(lmk->hash_tfm)] CRYPTO_MINALIGN_ATTR;
>> +	struct shash_desc *desc = (struct shash_desc *)sdesc;
> TBH, this looks even more uglier that the previous code :-)
I'm not claiming it's prettier. Merely C99. :)

> (But tglx already complained on different patch and I fully agree that crypto code
> should not use this kind of construction in the first place...
> It would be very nice to introduce at least some macro hiding these crazy
> stack allocations later.)
I actually agree with you and tglx. Will fix.

As I said to tglx, we were asked not to hide things with macro magic in 
some of our non-crypto VLAIS removal patches. Happy to use macros in 
this case.

Thanks,

Behan

-- 
Behan Webster
behanw@...verseincode.com

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