Kyrylo Tkachov kyrylo.tkachov@arm.com
Thu Aug 8 09:21:00 GMT 2013

> 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 defined by GCC when compiling for the ARMv2 architecture.
GCC defines an __ARM_ARCH_<architecture version>__ predefine when compiling
for a particular architecture.

In the snippet you posted it is used to make sure the code below the #ifndef
is not used/compiled when targeting ARMv2.


P.S. In the future, questions like these go on the gcc-help list. The gcc list
is used for discussions on the development of gcc.

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