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Date: Wed, 17 Sep 2014 08:26:19 -0700 From: Behan Webster <behanw@...verseincode.com> To: Herbert Xu <herbert@...dor.apana.org.au>, Dmitry Kasatkin <d.kasatkin@...sung.com> CC: agk@...hat.com, clm@...com, davem@...emloft.net, dm-devel@...hat.com, fabf@...net.be, jbacik@...com, snitzer@...hat.com, tadeusz.struk@...el.com, akpm@...ux-foundation.org, bruce.w.allan@...el.com, james.l.morris@...cle.com, john.griffin@...el.com, linux-btrfs@...r.kernel.org, linux-crypto@...r.kernel.org, linux-ima-devel@...ts.sourceforge.net, linux-ima-user@...ts.sourceforge.net, linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org, linux-security-module@...r.kernel.org, neilb@...e.de, qat-linux@...el.com, serge@...lyn.com, thomas.lendacky@....com, zohar@...ux.vnet.ibm.com, torvalds@...ux-foundation.org Subject: Re: [PATCH v3 01/12] crypto: LLVMLinux: Add macro to remove use of VLAIS in crypto code On 09/17/14 04:30, Herbert Xu wrote: > On Wed, Sep 17, 2014 at 02:15:40PM +0300, Dmitry Kasatkin wrote: >> On 17/09/14 12:22, Herbert Xu wrote: >>> On Mon, Sep 15, 2014 at 12:30:23AM -0700, behanw@...verseincode.com wrote: >>>> From: Behan Webster <behanw@...verseincode.com> >>>> >>>> Add a macro which replaces the use of a Variable Length Array In Struct (VLAIS) >>>> with a C99 compliant equivalent. This macro instead allocates the appropriate >>>> amount of memory using an char array. >>>> >>>> The new code can be compiled with both gcc and clang. >>>> >>>> struct shash_desc contains a flexible array member member ctx declared with >>>> CRYPTO_MINALIGN_ATTR, so sizeof(struct shash_desc) aligns the beginning >>>> of the array declared after struct shash_desc with long long. >>>> >>>> No trailing padding is required because it is not a struct type that can >>>> be used in an array. >>>> >>>> The CRYPTO_MINALIGN_ATTR is required so that desc is aligned with long long >>>> as would be the case for a struct containing a member with >>>> CRYPTO_MINALIGN_ATTR. >>>> >>>> Signed-off-by: Behan Webster <behanw@...verseincode.com> >>> Acked-by: Herbert Xu <herbert@...dor.apana.org.au> >>> >>> Thanks, >> Just in case. >> I would still follow advice from "Michał Mirosław" to use shash##__desc[] Absolutely. I will be posting a v4 patchset . Just waiting a bit more for more comments on v3. The macro from v4 will look like this which I believe will satisfy the concern and indeed be safer than my previous version. +#define SHASH_DESC_ON_STACK(shash, tfm) \ + char __##shash##_desc[sizeof(struct shash_desc) + \ + crypto_shash_descsize(tfm)] CRYPTO_MINALIGN_ATTR; \ + struct shash_desc *shash = (struct shash_desc *)__##shash##_desc Hmm. Is it worth adding a comment with this macro explaining the reason this works? Essentially much of what is in the commit message? > Oh yes of course. My ack is more about the approach. Wonderful! Indeed. I would have asked for you to wait for v4 anyways. :) Thank you, Behan -- Behan Webster behanw@...verseincode.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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