__ARM_ARCH_2__

[zhaobin xv]

Hi

In linux/arch/arm/boot/compressed/head.S:


#ifndef __ARM_ARCH_2__
        /*
         * Booting from Angel - need to enter SVC mode and disable
         * FIQs/IRQs (numeric definitions from angel arm.h source).
         * We only do this if we were in user mode on entry.
         */
        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 don't know what the"__ARM_ARCH_2__" mean?
"__ARM_ARCH_2__" is definded by gcc or definded byarmlinux?
where does it come from? what does it want to do?