Messages in this thread | | | Date | Sat, 1 May 2010 21:35:44 +0300 | From | Alexander Shishkin <> | Subject | Re: [RFC PATCH] create generic alignment api (v5) |
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On Sun, Mar 28, 2010 at 08:09:00 -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()
Do you plan to have this integrated to the mainline? I'd like to use one of these in my next version of the __xchg patch. So, do you need any help or feedback or whatnot with this one?
> 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> > CC: Russell King - ARM Linux <linux@arm.linux.org.uk> > Cc: Alexander Shishkin <virtuoso@slind.org>, > 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
Acked-by: Alexander Shishkin <virtuoso@slind.org>
> --- > include/linux/kernel.h | 45 +++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 41 insertions(+), 4 deletions(-) > > Index: linux-2.6-lttng/include/linux/kernel.h > =================================================================== > --- linux-2.6-lttng.orig/include/linux/kernel.h 2010-03-27 20:46:07.000000000 -0400 > +++ linux-2.6-lttng/include/linux/kernel.h 2010-03-28 20:06:27.000000000 -0400 > @@ -37,10 +37,47 @@ extern const char linux_proc_banner[]; > > #define STACK_MAGIC 0xdeadbeef > > -#define ALIGN(x,a) __ALIGN_MASK(x,(typeof(x))(a)-1) > -#define __ALIGN_MASK(x,mask) (((x)+(mask))&~(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 ALIGN(x, a) __ALIGN_MASK((x), (typeof(x)) (a) - 1) > +#define __ALIGN_MASK(x, mask) (((x) + (mask)) & ~(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), sizeof(*(obj))) > +#define object_align_floor(obj) PTR_ALIGN_FLOOR((obj), sizeof(*(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); > +} > > #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr)) > > > -- > Mathieu Desnoyers > Operating System Efficiency R&D Consultant > EfficiOS Inc. > http://www.efficios.com
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