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Re: Unaligned access in kernel on ARMv6+ (Re: CVS commit: src/sys/dev/usb)

On Sun, Jan 06, 2019 at 05:52:55AM -0800, Jason Thorpe wrote:
> That's probably a good idea in any case, because there will almost
> certainly be a performance benefit, but I still think ensuring that
> drivers don't perform unaligned accesses is desirable.

It is a bit tricky. We do this only when compiling for CPUs that can do
the unaligned access, i.e. when compiling kernels for arm v5 we tell
gcc to not generate unaligned access ops.

IIUC in this case the driver code was innocent (using proper memcpy),
but gcc optimized the memcpy (which was fine too, given the flags we
pass to it).


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