arch/arm/kernel/entry-header.S

#include <linux/config.h> /* for CONFIG_ARCH_xxxx */
#include <linux/linkage.h>

#include <asm/assembler.h>
#include <asm/constants.h>
#include <asm/errno.h>
#include <asm/hardware.h>
#include <asm/arch/irqs.h>
#include <asm/arch/entry-macro.S>

#ifndef MODE_SVC
#define MODE_SVC 0x13
#endif

	.macro	zero_fp
#ifdef CONFIG_FRAME_POINTER
	mov	fp, #0
#endif
	.endm

	.text

@ Bad Abort numbers
@ -----------------
@
#define BAD_PREFETCH	0
#define BAD_DATA	1
#define BAD_ADDREXCPTN	2
#define BAD_IRQ		3
#define BAD_UNDEFINSTR	4

#define PT_TRACESYS	0x00000002

@ OS version number used in SWIs
@  RISC OS is 0
@  RISC iX is 8
@
#define OS_NUMBER	9
#define ARMSWI_OFFSET	0x000f0000

@
@ Most of the stack format comes from struct pt_regs, but with
@ the addition of 8 bytes for storing syscall args 5 and 6.
@
#define S_OFF		8

/* 
 * The SWI code relies on the fact that R0 is at the bottom of the stack
 * (due to slow/fast restore user regs).
 */
#if S_R0 != 0
#error "Please fix"
#endif

#if __LINUX_ARM_ARCH__ >= 6
	.macro	disable_irq
	cpsid	i
	.endm

	.macro	enable_irq
	cpsie	i
	.endm
#else
	.macro	disable_irq
	msr	cpsr_c, #PSR_I_BIT | SVC_MODE
	.endm

	.macro	enable_irq
	msr	cpsr_c, #SVC_MODE
	.endm
#endif

	.macro	save_user_regs
	sub	sp, sp, #S_FRAME_SIZE
	stmia	sp, {r0 - r12}			@ Calling r0 - r12
	add	r8, sp, #S_PC
	stmdb	r8, {sp, lr}^			@ Calling sp, lr
	mrs	r8, spsr			@ called from non-FIQ mode, so ok.
	str	lr, [sp, #S_PC]			@ Save calling PC
	str	r8, [sp, #S_PSR]		@ Save CPSR
	str	r0, [sp, #S_OLD_R0]		@ Save OLD_R0
	.endm

	.macro	restore_user_regs
	ldr	r1, [sp, #S_PSR]		@ Get calling cpsr
	disable_irq ip				@ disable IRQs
	ldr	lr, [sp, #S_PC]!		@ Get PC
	msr	spsr_cxsf, r1			@ save in spsr_svc
	ldmdb	sp, {r0 - lr}^			@ Get calling r0 - lr
	mov	r0, r0
	add	sp, sp, #S_FRAME_SIZE - S_PC
	movs	pc, lr				@ return & move spsr_svc into cpsr
	.endm

/*
 * Must be called with IRQs already disabled.
 */
	.macro	fast_restore_user_regs
	ldr	r1, [sp, #S_OFF + S_PSR]	@ get calling cpsr
	ldr	lr, [sp, #S_OFF + S_PC]!	@ get pc
	msr	spsr_cxsf, r1			@ save in spsr_svc
	ldmdb	sp, {r1 - lr}^			@ get calling r1 - lr
	mov	r0, r0
	add	sp, sp, #S_FRAME_SIZE - S_PC
	movs	pc, lr				@ return & move spsr_svc into cpsr
	.endm

/*
 * Must be called with IRQs already disabled.
 */
	.macro	slow_restore_user_regs
	ldr	r1, [sp, #S_PSR]		@ get calling cpsr
	ldr	lr, [sp, #S_PC]!		@ get pc
	msr	spsr_cxsf, r1			@ save in spsr_svc
	ldmdb	sp, {r0 - lr}^			@ get calling r1 - lr
	mov	r0, r0
	add	sp, sp, #S_FRAME_SIZE - S_PC
	movs	pc, lr				@ return & move spsr_svc into cpsr
	.endm

	.macro	mask_pc, rd, rm
	.endm

	.macro	get_thread_info, rd
	mov	\rd, sp, lsr #13
	mov	\rd, \rd, lsl #13
	.endm

	.macro	alignment_trap, rbase, rtemp, sym
#ifdef CONFIG_ALIGNMENT_TRAP
#define OFF_CR_ALIGNMENT(x)	cr_alignment - x

	ldr	\rtemp, [\rbase, #OFF_CR_ALIGNMENT(\sym)]
	mcr	p15, 0, \rtemp, c1, c0
#endif
	.endm


/*
 * These are the registers used in the syscall handler, and allow us to
 * have in theory up to 7 arguments to a function - r0 to r6.
 *
 * r7 is reserved for the system call number for thumb mode.
 *
 * Note that tbl == why is intentional.
 *
 * We must set at least "tsk" and "why" when calling ret_with_reschedule.
 */
scno	.req	r7		@ syscall number
tbl	.req	r8		@ syscall table pointer
why	.req	r8		@ Linux syscall (!= 0)
tsk	.req	r9		@ current thread_info

/*
 * Get the system call number.
 */
	.macro	get_scno
#ifdef CONFIG_ARM_THUMB
	tst	r8, #PSR_T_BIT		@ this is SPSR from save_user_regs
	addne	scno, r7, #OS_NUMBER << 20 @ put OS number in
	ldreq	scno, [lr, #-4]

#else
	mask_pc	lr, lr
	ldr	scno, [lr, #-4]		@ get SWI instruction
#endif
	.endm