Inline assembly constraints for a specific register

[Avi Kivity <avi@xxxxxxxxxxxx>]

How can I specify a constraint for a specific register, for example r8 
on x86_64?

I can specify any of rax, rbx, rcx, and rdx using a,b, c, and d.  But 
what about the rest of the register file?

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error compiling committee.c: too many arguments to function