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Commit 9520b1a1 authored by Nicolas Pitre's avatar Nicolas Pitre
Browse files

ARM: head-common.S: speed up startup code 



Let's use optimized routines such as memcpy to copy .data and memzero
to clear .bss in the startup code instead of doing it one word at a
time. Those routines don't use any global data so they're safe to use
even if .data and .bss segments are not initialized.

In the .data copy case a temporary stack is installed in the .bss area
as the actual kernel stack is located within the copied data area. The
XIP kernel linker script ensures a 8 byte alignment for that purpose.

Finally, make the .data copy and related pointers surrounded by
CONFIG_XIP_KERNEL to make it obvious what it is all about. This will
allow for further cleanups in the non-XIP linker script.

Signed-off-by: default avatarNicolas Pitre <nico@linaro.org>
Reviewed-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: default avatarChris Brandt <Chris.Brandt@renesas.com>
parent 569dbb88

arch/arm/kernel/head-common.S

+44 −32
Original line number Diff line number Diff line
@@ -79,47 +79,59 @@ ENDPROC(__vet_atags) 
 */

	__INIT

__mmap_switched:

	adr	r3, __mmap_switched_data



	ldmia	r3!, {r4, r5, r6, r7}

	cmp	r4, r5				@ Copy data segment if needed

1:	cmpne	r5, r6

	ldrne	fp, [r4], #4

	strne	fp, [r5], #4

	bne	1b



	mov	fp, #0				@ Clear BSS (and zero fp)

1:	cmp	r6, r7

	strcc	fp, [r6],#4

	bcc	1b



 ARM(	ldmia	r3, {r4, r5, r6, r7, sp})

 THUMB(	ldmia	r3, {r4, r5, r6, r7}	)

 THUMB(	ldr	sp, [r3, #16]		)

	str	r9, [r4]			@ Save processor ID

	str	r1, [r5]			@ Save machine type

	str	r2, [r6]			@ Save atags pointer

	cmp	r7, #0

	strne	r0, [r7]			@ Save control register values



	mov	r7, r1

	mov	r8, r2

	mov	r10, r0



	adr	r4, __mmap_switched_data

	mov	fp, #0



#ifdef CONFIG_XIP_KERNEL

   ARM(	ldmia	r4!, {r0, r1, r2, sp} )

 THUMB(	ldmia	r4!, {r0, r1, r2, r3} )

 THUMB(	mov	sp, r3 )

	sub	r2, r2, r1

	bl	memcpy				@ copy .data to RAM

#endif



   ARM(	ldmia	r4!, {r0, r1, sp} )

 THUMB(	ldmia	r4!, {r0, r1, r3} )

 THUMB(	mov	sp, r3 )

	sub	r1, r1, r0

	bl	__memzero			@ clear .bss



	ldmia	r4, {r0, r1, r2, r3}

	str	r9, [r0]			@ Save processor ID

	str	r7, [r1]			@ Save machine type

	str	r8, [r2]			@ Save atags pointer

	cmp	r3, #0

	strne	r10, [r3]			@ Save control register values

	b	start_kernel

ENDPROC(__mmap_switched)



	.align	2

	.type	__mmap_switched_data, %object

__mmap_switched_data:

	.long	__data_loc			@ r4

	.long	_sdata				@ r5

	.long	__bss_start			@ r6

	.long	_end				@ r7

	.long	processor_id			@ r4

	.long	__machine_arch_type		@ r5

	.long	__atags_pointer			@ r6

#ifdef CONFIG_XIP_KERNEL

	.long	_sdata				@ r0

	.long	__data_loc			@ r1

	.long	_edata_loc			@ r2

	.long	__bss_stop			@ sp (temporary stack in .bss)

#endif



	.long	__bss_start			@ r0

	.long	__bss_stop			@ r1

	.long	init_thread_union + THREAD_START_SP @ sp



	.long	processor_id			@ r0

	.long	__machine_arch_type		@ r1

	.long	__atags_pointer			@ r2

#ifdef CONFIG_CPU_CP15

	.long	cr_alignment			@ r7

	.long	cr_alignment			@ r3

#else

	.long	0				@ r7

	.long	0				@ r3

#endif

	.long	init_thread_union + THREAD_START_SP @ sp

	.size	__mmap_switched_data, . - __mmap_switched_data



/*

arch/arm/kernel/vmlinux-xip.lds.S

+1 −1
Original line number Diff line number Diff line
@@ -301,7 +301,7 @@ SECTIONS 
	}

#endif



	BSS_SECTION(0, 0, 0)

	BSS_SECTION(0, 0, 8)

	_end = .;



	STABS_DEBUG