Re: Getting rid of alignment faults in userspace

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  char buf[8];
  void *v = &buf[1];
  unsigned int *p = (unsigned int *)v;

This does not (reliably) do what you expect. The compiler need not align buf.

Printing the value of p should clarify this.

And, as we can see above, the "simple" accesses are left to the hardware to fix up. However, if the misaligned access is performed using a 64-bit value pointer, then the kernel will trap an exception and the access will be simulated.

I think you've missed my point. gcc may (though unlikely in this case) choose to place buf at an odd address. In which case p will happen to be properly aligned.

I'm not sure where you get "64-bit value pointer" from. *p is only a word sized access, and memcpy is defined in terms of bytes so will only be promoted to wider accesses when the compiler believes it is safe.

Paul