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From: Tkhai Kirill <tkhai@yandex.ru>
To: sparclinux@vger.kernel.org
Subject: Re: [PATCH]SPARC32: Fixed unaligned memory copying in function __csum_partial_copy_sparc_generic
Date: Tue, 10 May 2011 23:21:49 +0000	[thread overview]
Message-ID: <414351305069709@web42.yandex.ru> (raw)
In-Reply-To: <1304845558.9492.14.camel@big>

11.05.11, 00:28, "David Miller" <davem@davemloft.net>:

>I don't understand why you're testing "andcc %o3, %o0, %g0", as %o3 has
>the value computed in "srl %g1, 1, %o3" here.

>What is so interesting about "ptr & (length >> 1)"?

1)Label ccte (rather, cc_end_cruft) copies data sequentially by pieces of length 2^x bytes from biggest to smallest. For example, if %g1 is 15, then the label copies 8+4+2+1\x15, and %o0 must be aligned to 8.

Let alignment a = 2^x. Pointer ptr % a = 0 when:
ptr & (a >> 1) = 0
ptr & (a >> 2) = 0
..

Or, what is the same:
ptr & (length >> 1) = 0
ptr & (length >> 2) = 0
..

I.e. we are looking for right alignment, if another case don't call ccte.

2)We check %o0 only, because %o1 has the same last two bits, and cc_end_cruft writes 4 bytes or less.

  parent reply	other threads:[~2011-05-10 23:21 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-08  9:05 [PATCH]SPARC32: Fixed unaligned memory copying in function kirill
2011-05-08 23:44 ` David Miller
2011-05-09  8:49 ` [PATCH]SPARC32: Fixed unaligned memory copying in function __csum_partial_copy_sparc_generic Tkhai Kirill
2011-05-09 18:33 ` [PATCH]SPARC32: Fixed unaligned memory copying in function David Miller
2011-05-09 19:55 ` [PATCH]SPARC32: Fixed unaligned memory copying in function __csum_partial_copy_sparc_generic Tkhai Kirill
2011-05-10 12:31 ` Tkhai Kirill
2011-05-10 20:28 ` [PATCH]SPARC32: Fixed unaligned memory copying in function David Miller
2011-05-10 23:21 ` Tkhai Kirill [this message]
2011-05-11 12:53 ` [PATCH]SPARC32: Fixed unaligned memory copying in function __csum_partial_copy_sparc_generic Daniel Hellstrom
2011-05-11 17:10 ` [PATCH]SPARC32: Fixed unaligned memory copying in function David Miller
2011-05-12  4:38 ` David Miller

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