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From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linux-arch <linux-arch@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	Aleksa Sarai <cyphar@cyphar.com>, Ingo Molnar <mingo@kernel.org>,
	Khalid Aziz <khalid.aziz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"open list:SYNOPSYS ARC ARCHITECTURE"
	<linux-snps-arc@lists.infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 4/4] ARC: uaccess: use optimized generic __strnlen_user/__strncpy_from_user
Date: Tue, 14 Jan 2020 21:36:15 +0000
Message-ID: <3734021d-1756-3a09-6595-14ca58c64bf9@synopsys.com> (raw)
In-Reply-To: <CAK8P3a2GUqmcA_q33=20OrK1+cU4f3mCrgci_bO3ho4B5PRODg@mail.gmail.com>

On 1/14/20 12:42 PM, Arnd Bergmann wrote:
> On Tue, Jan 14, 2020 at 9:08 PM Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote:
> 
>> diff --git a/arch/arc/include/asm/word-at-a-time.h b/arch/arc/include/asm/word-at-a-time.h
>> new file mode 100644
>> index 000000000000..00e92be70987
>> --- /dev/null
>> +++ b/arch/arc/include/asm/word-at-a-time.h
>> @@ -0,0 +1,49 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Copyright (C) 2020 Synopsys Inc.
>> + */
>> +#ifndef __ASM_ARC_WORD_AT_A_TIME_H
>> +#define __ASM_ARC_WORD_AT_A_TIME_H
>> +
>> +#ifdef __LITTLE_ENDIAN__
>> +
>> +#include <linux/kernel.h>
>> +
>> +struct word_at_a_time {
>> +       const unsigned long one_bits, high_bits;
>> +};
> 
> What's wrong with the generic version on little-endian? Any
> chance you can find a way to make it work as well for you as
> this copy?

find_zero() by default doesn't use pop count instructions. I didn't like the copy
either but wasn't sure of the best way to make this 4 API interface reusable. Are
you suggesting we allow partial over-ride starting with #ifndef find_zero ?

>> +static inline unsigned long find_zero(unsigned long mask)
>> +{
>> +#ifdef CONFIG_64BIT
>> +       return fls64(mask) >> 3;
>> +#else
>> +       return fls(mask) >> 3;
>> +#endif
> 
> The CONFIG_64BIT check not be needed, unless you are adding
> support for 64-bit ARC really soon.

:-) Indeed that was the premise !

Thx for the quick review.

-Vineet
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Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-14 20:08 [RFC 0/4] Switching ARC to optimized generic strncpy_from_user Vineet Gupta
2020-01-14 20:08 ` [RFC 1/4] asm-generic/uaccess: don't define inline functions if noinline lib/* in use Vineet Gupta
2020-01-14 20:57   ` Arnd Bergmann
2020-01-15 23:01     ` Vineet Gupta
2020-01-16 11:43       ` Arnd Bergmann
2020-01-14 21:32   ` Linus Torvalds
2020-01-15  9:08     ` Arnd Bergmann
2020-01-15 14:12       ` Al Viro
2020-01-15 14:21         ` Arnd Bergmann
2020-01-14 20:08 ` [RFC 2/4] lib/strncpy_from_user: Remove redundant user space pointer range check Vineet Gupta
2020-01-14 21:22   ` Linus Torvalds
2020-01-14 21:52     ` Vineet Gupta
2020-01-14 23:46     ` Al Viro
2020-01-15 14:42   ` Andrey Konovalov
2020-01-15 23:00     ` Vineet Gupta
2020-01-14 20:08 ` [RFC 3/4] ARC: uaccess: remove noinline variants of __strncpy_from_user() and friends Vineet Gupta
2020-01-14 20:08 ` [RFC 4/4] ARC: uaccess: use optimized generic __strnlen_user/__strncpy_from_user Vineet Gupta
2020-01-14 20:42   ` Arnd Bergmann
2020-01-14 21:36     ` Vineet Gupta [this message]
2020-01-14 21:49       ` Linus Torvalds
2020-01-14 22:14         ` Vineet Gupta

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