malloc memory to be 32 byte aligned in kernel

[Valdis.Kletnieks at vt.edu]

On Tue, 28 Jan 2014 15:32:37 -0800, anish singh said:
> On Tue, Jan 28, 2014 at 11:20 AM, m silverstri
> <michael.j.silverstri at gmail.com> wrote:
> > Hi,
> >
> > I am writing a kernel driver, can you please tell me how can I
> > allocate a buffer which is 32 byte aligned?
> malloc already aligns memory for basic data types AFAIK

Yes, but even if it allocates on a long-long boundary, he can still get
hosed if it ends up on a 8-byte boundary that's *not* a 32-byte aligned.

Your best approach is probably to use the KMEM_CACHE() macro to create a slab
cache, and then allocate from that slab.  See include/linux/slab.h

/*
 * Please use this macro to create slab caches. Simply specify the
 * name of the structure and maybe some flags that are listed above.
 *
 * The alignment of the struct determines object alignment. If you
 * f.e. add ____cacheline_aligned_in_smp to the struct declaration
 * then the objects will be properly aligned in SMP configurations.
 */
#define KMEM_CACHE(__struct, __flags) kmem_cache_create(#__struct,                sizeof(struct __struct), __alignof__(struct __struct),                (__flags), NULL)

Oh, and you'll need to declare a 'struct foo {...} __attribute__(aligned(32))'
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