freebsd-dev/sys/arm/include/_align.h
Ian Lepore da6da1575b Adjust _ALIGNBYTES to the proper value for arm and armv6 arches. Modern
compilers can emit arm instructions that require 8-byte alignment.  The
alignment-sensitive instructions were added in armv5, which has to be
supported by our combined v4/v5 kernels, so the value is set uncoditionally
for all arm architecture versions.

Also adjust the comment to explain in more detail why the macros have the
form and values they do.

Per advice from bde@, maintain the unsignedness of the value of _ALIGNBYTES
(but do so using his second choice of allowing sizeof() to supply the
unsignedness, rather than just hardcoding '8U', which in my mind would
require an even more verbose comment to explain why it's right).  Also
explain in the comment that the resulting type of _ALIGN() is equivelent
to uinptr_t on arm (32-bit unsigned int), but it's purposely spelled as
"unsigned" to avoid problems with including other header files.  Even
including machine/_types.h to allow use of __uintptr_t causes compilation
failures because of this header being included (indirectly) in asm code.

The discussion that led to this change (albeit at a glacial pace) is at
https://lists.freebsd.org/pipermail/svn-src-head/2014-November/064593.html
2016-05-21 16:52:38 +00:00

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/*-
* Copyright (c) 2001 David E. O'Brien
* Copyright (c) 1990 The Regents of the University of California.
* All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* William Jolitz.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* from: @(#)param.h 5.8 (Berkeley) 6/28/91
* $FreeBSD$
*/
#ifndef _ARM_INCLUDE__ALIGN_H_
#define _ARM_INCLUDE__ALIGN_H_
/*
* Round p (pointer or byte index) up to the hardware-required alignment which
* is sufficient for any data type, pointer or numeric. The resulting type
* is equivelent to arm's uintptr_t (but is purposely spelled "unsigned" here).
*/
#define _ALIGNBYTES (sizeof(long long) - 1)
#define _ALIGN(p) (((unsigned)(p) + _ALIGNBYTES) & ~_ALIGNBYTES)
#endif /* !_ARM_INCLUDE__ALIGN_H_ */