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https://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongson
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a1f98849fd
This allows for optional alternative implementations of __copy_to_user and __clear_user, with a possible runtime fallback to the standard version when the alternative provides no gain over that standard version. This is done by making the standard __copy_to_user into a weak alias for the symbol __copy_to_user_std. Same thing for __clear_user. Those two functions are particularly good candidates to have alternative implementations for, since they rely on the STRT instruction which has lower performances than STM instructions on some CPU cores such as the ARM1176 and Marvell Feroceon. Signed-off-by: Nicolas Pitre <nico@marvell.com>
55 lines
1.3 KiB
ArmAsm
55 lines
1.3 KiB
ArmAsm
/*
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* linux/arch/arm/lib/clear_user.S
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*
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* Copyright (C) 1995, 1996,1997,1998 Russell King
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/linkage.h>
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#include <asm/assembler.h>
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.text
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/* Prototype: int __clear_user(void *addr, size_t sz)
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* Purpose : clear some user memory
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* Params : addr - user memory address to clear
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* : sz - number of bytes to clear
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* Returns : number of bytes NOT cleared
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*/
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ENTRY(__clear_user_std)
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WEAK(__clear_user)
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stmfd sp!, {r1, lr}
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mov r2, #0
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cmp r1, #4
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blt 2f
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ands ip, r0, #3
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beq 1f
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cmp ip, #2
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USER( strbt r2, [r0], #1)
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USER( strlebt r2, [r0], #1)
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USER( strltbt r2, [r0], #1)
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rsb ip, ip, #4
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sub r1, r1, ip @ 7 6 5 4 3 2 1
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1: subs r1, r1, #8 @ -1 -2 -3 -4 -5 -6 -7
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USER( strplt r2, [r0], #4)
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USER( strplt r2, [r0], #4)
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bpl 1b
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adds r1, r1, #4 @ 3 2 1 0 -1 -2 -3
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USER( strplt r2, [r0], #4)
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2: tst r1, #2 @ 1x 1x 0x 0x 1x 1x 0x
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USER( strnebt r2, [r0], #1)
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USER( strnebt r2, [r0], #1)
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tst r1, #1 @ x1 x0 x1 x0 x1 x0 x1
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USER( strnebt r2, [r0])
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mov r0, #0
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ldmfd sp!, {r1, pc}
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ENDPROC(__clear_user)
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.section .fixup,"ax"
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.align 0
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9001: ldmfd sp!, {r0, pc}
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.previous
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