Messages in this thread | | | Date | Wed, 18 Aug 2010 03:00:56 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [RFC PATCH 01/20] Create generic alignment API (v8) |
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On Tue, Aug 17, 2010 at 07:16:20PM -0400, Mathieu Desnoyers wrote: > Rather than re-doing the "alignment on a type size" trick all over again at > different levels, import the "ltt_align" from LTTng into kernel.h and make this > available to everyone. Renaming to: > > - object_align() > - object_align_floor() > - offset_align() > - offset_align_floor() > > Changelog since v7: > - Add missing include/linux/Kconfig header-y. > > Changelog since v6: > - Adapt to changes introduced by > commit a79ff731a1b277d0e92d9453bdf374e04cec717a > - Use __alignof__() instead of sizeof() to support compound types. > > Changelog since v5: > - moved alignment apis to a separate header file so that it is possible > to use them from other header files which are, for example, included > from kernel.h. > > Changelog since v4: > - add missing ( ) around parameters within object_align() and > object_align_floor(). > - More coding style cleanups to ALIGN() (checkpatch.pl is happy now). > > Changelog since v3: > - optimize object_align*() so fewer instructions are needed for alignment of > addresses known dynamically. Use the (already existing) "ALIGN()", and create > the "ALIGN_FLOOR()" macro. > - While we are there, let's clean up the ALIGN() macros wrt coding style. e.g. > missing parenthesis around the first use of the "x" parameter in ALIGN(). > > Changelog since v2: > - Fix object_align*(): should use object size alignment, not pointer alignment. > > Changelog since v1: > - Align on the object natural alignment > (rather than min(arch word alignment, natural alignment)) > > The advantage of separating the API in "object alignment" and "offset alignment" > is that it gives more freedom to play with offset alignment. Very useful to > implement a tracer ring-buffer alignment. (hint hint) > > Typical users will use "object alignment", but infrastructures like tracers > which need to perform alignment of statically known base+offsets will typically > use "offset alignment", because it allows to align with respect to a base rather > than to pass an absolute address. > > We use "sizeof(object)" rather than "__alignof__()" object because alignof > returns "recommended" object alignment for the architecture, which can be > sub-optimal on some architectures. By ensuring alignment on the object size, we > are sure to make the right choice. > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > Signed-off-by: Alexander Shishkin <virtuoso@slind.org> > CC: Russell King - ARM Linux <linux@arm.linux.org.uk> > CC: linux-arm-kernel@lists.infradead.org > CC: Imre Deak <imre.deak@nokia.com> > CC: Jamie Lokier <jamie@shareable.org> > CC: rostedt@goodmis.org > CC: mingo@elte.hu > CC: Alexey Dobriyan <adobriyan@gmail.com> > --- > include/linux/Kbuild | 1 > include/linux/align.h | 56 +++++++++++++++++++++++++++++++++++++++++++++++++ > include/linux/kernel.h | 8 ------- > 3 files changed, 58 insertions(+), 7 deletions(-) > create mode 100644 include/linux/align.h > > Index: linux.trees.git/include/linux/align.h > =================================================================== > --- /dev/null 1970-01-01 00:00:00.000000000 +0000 > +++ linux.trees.git/include/linux/align.h 2010-08-17 16:31:50.000000000 -0400 > @@ -0,0 +1,56 @@ > +#ifndef _LINUX_ALIGN_H > +#define _LINUX_ALIGN_H > + > +#define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK((x), (typeof(x))(a) - 1) ^^^ Unnecessary braces. And many below.
> +#define __ALIGN_KERNEL_MASK(x, mask) \ > + (((x) + (mask)) & ~(mask)) > + > +#ifdef __KERNEL__ > + > +#include <linux/types.h> > + > +#define ALIGN(x, a) __ALIGN_KERNEL((x), (a)) > +#define __ALIGN_MASK(x, mask) __ALIGN_KERNEL_MASK((x), (mask)) > +#define PTR_ALIGN(p, a) ((typeof(p)) ALIGN((unsigned long) (p), (a))) > +#define ALIGN_FLOOR(x, a) __ALIGN_FLOOR_MASK((x), (typeof(x)) (a) - 1) > +#define __ALIGN_FLOOR_MASK(x, mask) ((x) & ~(mask)) > +#define PTR_ALIGN_FLOOR(p, a) \ > + ((typeof(p)) ALIGN_FLOOR((unsigned long) (p), (a))) > +#define IS_ALIGNED(x, a) (((x) & ((typeof(x)) (a) - 1)) == 0) > + > +/* > + * Align pointer on natural object alignment. Object size must be power of two. > + */ > +#define object_align(obj) PTR_ALIGN((obj), __alignof__(*(obj))) > +#define object_align_floor(obj) PTR_ALIGN_FLOOR((obj), __alignof__(*(obj))) > + > +/** > + * offset_align - Calculate the offset needed to align an object on its natural > + * alignment towards higher addresses. > + * @align_drift: object offset from an "alignment"-aligned address. > + * @alignment: natural object alignment. Must be non-zero, power of 2. > + * > + * Returns the offset that must be added to align towards higher > + * addresses. > + */ > +static inline size_t offset_align(size_t align_drift, size_t alignment) > +{ > + return (alignment - align_drift) & (alignment - 1); > +} > + > +/** > + * offset_align_floor - Calculate the offset needed to align an object > + * on its natural alignment towards lower addresses. > + * @align_drift: object offset from an "alignment"-aligned address. > + * @alignment: natural object alignment. Must be non-zero, power of 2. > + * > + * Returns the offset that must be substracted to align towards lower addresses. > + */ > +static inline size_t offset_align_floor(size_t align_drift, size_t alignment) > +{ > + return (align_drift - alignment) & (alignment - 1); > +} > + > +#endif /* __KERNEL__ */ > + > +#endif > Index: linux.trees.git/include/linux/kernel.h > =================================================================== > --- linux.trees.git.orig/include/linux/kernel.h 2010-08-17 16:28:25.000000000 -0400 > +++ linux.trees.git/include/linux/kernel.h 2010-08-17 16:31:50.000000000 -0400 > @@ -4,8 +4,7 @@ > /* > * 'kernel.h' contains some often-used function prototypes etc > */ > -#define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK(x, (typeof(x))(a) - 1) > -#define __ALIGN_KERNEL_MASK(x, mask) (((x) + (mask)) & ~(mask)) > +#include <linux/align.h> > > #ifdef __KERNEL__ > > @@ -39,11 +38,6 @@ extern const char linux_proc_banner[]; > > #define STACK_MAGIC 0xdeadbeef > > -#define ALIGN(x, a) __ALIGN_KERNEL((x), (a)) > -#define __ALIGN_MASK(x, mask) __ALIGN_KERNEL_MASK((x), (mask)) > -#define PTR_ALIGN(p, a) ((typeof(p))ALIGN((unsigned long)(p), (a))) > -#define IS_ALIGNED(x, a) (((x) & ((typeof(x))(a) - 1)) == 0) > - > #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr)) > > /* > Index: linux.trees.git/include/linux/Kbuild > =================================================================== > --- linux.trees.git.orig/include/linux/Kbuild 2010-08-17 16:28:25.000000000 -0400 > +++ linux.trees.git/include/linux/Kbuild 2010-08-17 16:32:30.000000000 -0400 > @@ -38,6 +38,7 @@ header-y += adfs_fs.h > header-y += affs_hardblocks.h > header-y += agpgart.h > header-y += aio_abi.h > +header-y += align.h > header-y += apm_bios.h > header-y += arcfb.h > header-y += atalk.h > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
-- Kirill A. Shutemov
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