> As far as I know, it is an old (and documented) flaw of gcc: it needs 
> at
> least -O in order to get inline assembly correctly (the binding of 
> local
> variables to register is not handled properly by the dummy register
> allocator used when compiling without optimisations). And the kernel
> uses inline assembly to talk to the hardware.
>
I guess this actually enough of a problem to warrant a pr - and I just 
did a quick search and saw toolchain/18270.  From what I can see, COPTS 
is reset even if "+=" is used.  I'll see if I can just append my 
observations to the PR.  At the very least, it's a documentation bug in 
mk.conf(5)...

Joe.