Re: [Bluez-devel] Alignment issue

[Marcel Holtmann <marcel@holtmann.org>]

Hi David,

> > > The attached patch should fix the problem (it does as far as I can tell).
> > > The compiler probably thinks both arguments to memcpy() are aligned and so
> > > makes an optimization which breaks the copy (because the destination is not
> > > actually aligned). Perhaps this is a compiler bug... I'm using gcc 3.3.3.
> > > After googling and reading some discussion on the topic it seems that it's
> > > probably not a compiler bug. I'll leave that for someone else to decide. :)
> > 
> > after checking some more resources, you may be right and the compiler
> > optimizes here where it should not. I found a comment about gcc and
> > using its __builtin_memcpy. Try to replace the memcpy with memmove and
> > see if this works.
> 
> That isn't guaranteed to work either. This is the patch I've been
> testing in the Fedora RPM since August. It lets the compiler know what's
> happening so it can generate optimal code.

why using a do-while for put_unaligned() and not for get_unaligned(). Is
this supposed to work with each GCC version? Will it also work with
other compilers? What about performance? If a platform can do unaligned
access by itself it should be faster than compiler tricks.

Regards

Marcel




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