angel_SWI_ARM

[zhaobin xv]

Hello
when I read linux/arch/arm/boot/compressed/head.S
I can't understand :
 mrs    r2, cpsr        @ get current mode
        tst    r2, #3            @ not user?
        bne    not_angel
        mov    r0, #0x17        @ angel_SWIreason_EnterSVC
        swi    0x123456        @ angel_SWI_ARM
I want to know :
a) what is angel_SWI_ARM
b) what is angel debuger
c)Do the code " swi    0x123456 " make interrupt what make program
jump to addr 0x0000 0008
,but addr 0x0000 0008 doesn't initialize.