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

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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: Nicolas Pitre <nico@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Chris Brandt <Chris.Brandt@renesas.com>
This commit is contained in:
Nicolas Pitre 2017-08-24 15:54:47 -04:00
parent 569dbb88e8
commit 9520b1a1b5
2 changed files with 43 additions and 31 deletions
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72
arch/arm/kernel/head-common.S
View file

@ -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 r7, r1
mov r8, r2
mov r10, r0
mov fp, #0 @ Clear BSS (and zero fp)
1: cmp r6, r7
strcc fp, [r6],#4
bcc 1b
adr r4, __mmap_switched_data
mov fp, #0
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
#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_CPU_CP15
.long cr_alignment @ r7
#else
.long 0 @ r7
#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 @ r3
#else
.long 0 @ r3
#endif
.size __mmap_switched_data, . - __mmap_switched_data
/*

2
arch/arm/kernel/vmlinux-xip.lds.S
View file

@ -301,7 +301,7 @@ SECTIONS
}
#endif
BSS_SECTION(0, 0, 0)
BSS_SECTION(0, 0, 8)
_end = .;
STABS_DEBUG