Macro hvc1 

macro_rules! hvc1 {
    ($num:expr, $arg0:expr) => { ... };
}

Generate an HVC call with 1 parameters

Puts the first argument in the instruction, and the parameter in r0. Gives you back the value left in r0 by the handler.

const HYPERCALL_FOO: u32 = 0x100;
let result = hvc1!(0x00, HYPERCALL_FOO);