From: Dmitry Vyukov <dvyukov@google.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Michael Davidson <md@google.com>,
Alexander Potapenko <glider@google.com>,
Michal Marek <mmarek@suse.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Herbert Xu <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>,
Shaohua Li <shli@kernel.org>,
Matthias Kaehlcke <mka@chromium.org>,
"x86@kernel.org" <x86@kernel.org>,
"open list:KERNEL BUILD + fi..." <linux-kbuild@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-crypto@vger.kernel.org, linux-raid@vger.kernel.org
Subject: Re: [PATCH 6/7] md/raid10, LLVM: get rid of variable length array
Date: Fri, 24 Mar 2017 14:47:15 +0100 [thread overview]
Message-ID: <CACT4Y+awYCAwoCkh8PQ-i2BdkxeuFp9meVXp=Yv6hGY8YjDnQg@mail.gmail.com> (raw)
In-Reply-To: <96158847-4F1F-4293-8435-E111F39E3260@zytor.com>
On Fri, Mar 17, 2017 at 9:04 PM, <hpa@zytor.com> wrote:
> On March 17, 2017 12:27:46 PM PDT, Peter Zijlstra <peterz@infradead.org> wrote:
>>On Fri, Mar 17, 2017 at 11:52:01AM -0700, Michael Davidson wrote:
>>> On Fri, Mar 17, 2017 at 5:44 AM, Peter Zijlstra
>><peterz@infradead.org> wrote:
>>> >
>>> > Be that as it may; what you construct above is disgusting. Surely
>>the
>>> > code can be refactored to not look like dog vomit?
>>> >
>>> > Also; its not immediately obvious conf->copies is 'small' and this
>>> > doesn't blow up the stack; I feel that deserves a comment
>>somewhere.
>>> >
>>>
>>> I agree that the code is horrible.
>>>
>>> It is, in fact, exactly the same solution that was used to remove
>>> variable length arrays in structs from several of the crypto drivers
>>a
>>> few years ago - see the definition of SHASH_DESC_ON_STACK() in
>>> "crypto/hash.h" - I did not, however, hide the horrors in a macro
>>> preferring to leave the implementation visible as a warning to
>>whoever
>>> might touch the code next.
>>>
>>> I believe that the actual stack usage is exactly the same as it was
>>previously.
>>>
>>> I can certainly wrap this up in a macro and add comments with
>>> appropriately dire warnings in it if you feel that is both necessary
>>> and sufficient.
>>
>>We got away with ugly in the past, so we should get to do it again?
>
> Seriously, you should have taken the hack the first time that this needs to be fixed. Just because this is a fairly uncommon construct in the kernel doesn't mean it is not in userspace.
There is a reason why it is fairly uncommon in kernel.
Initially it was used more widely, but then there was a decision to
drop all uses of this feature. Namely:
Linus: "We should definitely drop it. The feature is an abomination".
https://lkml.org/lkml/2013/9/23/500
I really don't understand why you cling onto this last use of the
feature. Having a single use of a compiler extension on an error path
of a non-mandatory driver does not look like a great idea to me. Let's
just kill it off outside of clang discussion.
next prev parent reply other threads:[~2017-03-24 13:47 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-17 0:15 [PATCH 0/7] LLVM: make x86_64 kernel build with clang Michael Davidson
2017-03-17 0:15 ` [PATCH 1/7] Makefile, LLVM: add -no-integrated-as to KBUILD_[AC]FLAGS Michael Davidson
2017-04-03 22:49 ` Matthias Kaehlcke
2017-04-21 7:49 ` Masahiro Yamada
2017-03-17 0:15 ` [PATCH 2/7] Makefile, x86, LLVM: disable unsupported optimization flags Michael Davidson
2017-03-17 21:32 ` H. Peter Anvin
2017-03-17 21:34 ` H. Peter Anvin
2017-04-05 18:08 ` Masahiro Yamada
2017-04-05 19:01 ` Matthias Kaehlcke
2017-04-05 19:11 ` Michael Davidson
2017-04-10 14:54 ` Masahiro Yamada
2017-03-17 0:15 ` [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned accesses Michael Davidson
2017-03-17 23:50 ` hpa
2017-04-03 23:01 ` Matthias Kaehlcke
2017-04-13 23:14 ` Matthias Kaehlcke
2017-04-13 23:55 ` H. Peter Anvin
2017-04-14 0:23 ` Matthias Kaehlcke
2017-04-14 5:30 ` hpa
2017-03-17 0:15 ` [PATCH 4/7] x86, boot, LLVM: #undef memcpy etc in string.c Michael Davidson
2017-06-22 22:31 ` Matthias Kaehlcke
2017-06-22 22:37 ` H. Peter Anvin
2017-06-30 18:32 ` Matthias Kaehlcke
2017-03-17 0:15 ` [PATCH 5/7] x86, boot, LLVM: Use regparm=0 for memcpy and memset Michael Davidson
2017-03-17 12:08 ` Peter Zijlstra
2017-06-22 22:38 ` H. Peter Anvin
2017-03-17 0:15 ` [PATCH 6/7] md/raid10, LLVM: get rid of variable length array Michael Davidson
2017-03-17 12:08 ` Peter Zijlstra
2017-03-17 12:31 ` Alexander Potapenko
2017-03-17 12:32 ` Alexander Potapenko
2017-03-17 18:03 ` Borislav Petkov
2017-03-17 18:47 ` Dmitry Vyukov
2017-03-17 18:57 ` Borislav Petkov
2017-03-17 19:05 ` Dmitry Vyukov
2017-03-17 19:26 ` Peter Zijlstra
2017-03-17 19:29 ` Peter Zijlstra
2017-03-24 13:50 ` Dmitry Vyukov
2017-03-24 14:10 ` Peter Zijlstra
2017-03-24 14:22 ` Dmitry Vyukov
2017-03-18 0:41 ` Fengguang Wu
2017-03-17 12:44 ` Peter Zijlstra
2017-03-17 18:52 ` Michael Davidson
2017-03-17 19:27 ` Peter Zijlstra
2017-03-17 20:04 ` hpa
2017-03-24 13:47 ` Dmitry Vyukov [this message]
2017-03-24 14:09 ` Peter Zijlstra
2017-03-17 0:15 ` [PATCH 7/7] crypto, x86, LLVM: aesni - fix token pasting Michael Davidson
2017-04-03 23:14 ` Matthias Kaehlcke
2017-03-17 8:17 ` [PATCH 0/7] LLVM: make x86_64 kernel build with clang Dmitry Vyukov
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