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Commit 11539337 authored by Alexey Dobriyan's avatar Alexey Dobriyan Committed by Ingo Molnar
Browse files

x86/asm/64: Micro-optimize __clear_user() - Use immediate constants 



Save two registers. Adding constants should be just as fast as adding registers.

Signed-off-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180507213937.GB32406@avx2


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 67b8d5c7

arch/x86/lib/usercopy_64.c

+4 −5
Original line number Diff line number Diff line
@@ -23,13 +23,13 @@ unsigned long __clear_user(void __user *addr, unsigned long size) 
	asm volatile(

		"	testq  %[size8],%[size8]\n"

		"	jz     4f\n"

		"0:	movq %[zero],(%[dst])\n"

		"	addq   %[eight],%[dst]\n"

		"0:	movq $0,(%[dst])\n"

		"	addq   $8,%[dst]\n"

		"	decl %%ecx ; jnz   0b\n"

		"4:	movq  %[size1],%%rcx\n"

		"	testl %%ecx,%%ecx\n"

		"	jz     2f\n"

		"1:	movb   %b[zero],(%[dst])\n"

		"1:	movb   $0,(%[dst])\n"

		"	incq   %[dst]\n"

		"	decl %%ecx ; jnz  1b\n"

		"2:\n"
@@ -40,8 +40,7 @@ unsigned long __clear_user(void __user *addr, unsigned long size) 
		_ASM_EXTABLE(0b,3b)

		_ASM_EXTABLE(1b,2b)

		: [size8] "=&c"(size), [dst] "=&D" (__d0)

		: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr),

		  [zero] "r" (0UL), [eight] "r" (8UL));

		: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr));

	clac();

	return size;

}