Macro svc6 

macro_rules! svc6 {
    ($num:expr, $arg0:expr, $arg1:expr, $arg2:expr, $arg3:expr, $arg4:expr, $arg5:expr) => { ... };
}

Generate an SVC call with 6 parameters

Puts the first argument in the instruction, and the parameters in r0-r5. Gives you back the value left in r0 by the handler.

const SYSCALL_FOO: u32 = 0x100;
let result = svc6!(0x00, SYSCALL_FOO, 1, 2, 3, 4, 5);