On Friday 20 July 2012 07:31:47 Marek Vasut wrote: > Dear Mike Frysinger, > > On Saturday 07 July 2012 23:08:14 Marek Vasut wrote: > > > +/* > > > DEFINE_CACHE_ALIGN_BUFFER() is similar to ALLOC_CACHE_ALIGN_BUFFER, > > > but it's purpose is to allow allocating aligned buffers outside of > > > function scope. Usage of this macro shall be avoided or used with > > > extreme care! */ > > > +#define DEFINE_CACHE_ALIGN_BUFFER(type, name, size) > > > + static char __##name[roundup(size * sizeof(type), ARCH_DMA_MINALIGN)] > > > + __aligned(ARCH_DMA_MINALIGN); > > > + static type *name = (type *)__##name; > > > > how is this any different from doing: > > static __u8 foo[1234] __aligned(ARCH_DMA_MINALIGN); > > Does __aligned() align both start of the buffer downwards and end of it > upwards ?
it guarantees the start is aligned. i don't believe it does any tail padding.
that said, you've added just 1 consumer, but it uses in function scope, so i
don't see why you had to define a new helper in the first place. the existing
one would work fine shouldn't it ?
you should probably add a const to the 2nd part so gcc is more likely to
optimize away the storage:
static type * const name = (type *)__##name;
otherwise older gcc versions will create a pointer to go through rather than
having things directly access the buffer.
w/out const:
$ readelf -s a.out | grep foo
11: 00000000004005d0 8 OBJECT LOCAL DEFAULT 13 foo.1592
12: 0000000000402080 96 OBJECT LOCAL DEFAULT 25 __foo.1591
w/const:
$ readelf -s a.out | grep foo
11: 0000000000402080 96 OBJECT LOCAL DEFAULT 25 __foo.1591
-mike
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