Re: [linux-usb] How to get aligned memory?
Fri, 31 Jul 1998 15:25:41 +0200

On Fri, Jul 31, 1998 at 10:15:21AM +0200, Nick Hibma wrote:

> > This is a so silly question I feel dumb for not having able to
> > find it myself ... how can I get aligned memory?
> >
> > The problem is I have this structure, 64 bits long which needs
> > to be aligned to 16 bytes (thx, Intel >:), but I cannot find my to do
> > it (except to allocate a lot until I get it aligned, which is quite
> > wasteful :).
> Have a look at the malloc man page. I think it tells you that a block of
> n bytes (n a power of two) is aligned to the nearest higher power of
> two, guarantueed. At least that is the way the Framelist is aligned in
> my code. I do check that in debugging mode but it has not failed up to
> now.

First: malloc gives only the limited guarantee about alignment that the
alignment is sufficient for storing any basic type or structure. Otherwise
constructs like

double *blurb;

blurb = malloc(sizeof(double));

*blurb = 42.0;

might bomb on certain architectures or have to take a serious performance

Second: the original poster was asking about allocation of aligned memory
in the kernel. And in the kernel there is no malloc(3).


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