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Subject[patch 12/13] syslets: x86: optimized copy_uatom()
From: Ingo Molnar <mingo@elte.hu>

provide an optimized assembly version of the copy_uatom() method.
This is about 3 times faster than the C version.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
---
arch/i386/lib/getuser.S | 115 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 115 insertions(+)

Index: linux/arch/i386/lib/getuser.S
===================================================================
--- linux.orig/arch/i386/lib/getuser.S
+++ linux/arch/i386/lib/getuser.S
@@ -10,6 +10,121 @@
*/
#include <asm/thread_info.h>

+/*
+ * copy_uatom() - copy a syslet_atom from user-space into kernel-space:
+ */
+
+.text
+.align 4
+.globl copy_uatom
+copy_uatom:
+ #
+ # regparm(2) call, %eax: atom, %edx: uatom
+ #
+ movl %eax, %ecx # %ecx is atom, %edx remains uatom
+
+ cmpl $__PAGE_OFFSET-40, %edx # access_ok(uatom-sizeof(*uatom))
+ jae bad_copy_uatom
+
+
+1: movl (%edx), %eax # atom->flags = uatom->flags
+ movl %eax, (%ecx)
+
+2: movl 4(%edx), %eax # atom->nr = uatom->nr
+ movl %eax, 4(%ecx)
+
+3: movl 8(%edx), %eax # atom->ret_ptr = uatom->ret_ptr
+ movl %eax, 8(%ecx)
+
+4: movl 12(%edx), %eax # atom->next = uatom->next
+ movl %eax, 12(%ecx)
+
+
+10: movl 16(%edx), %eax # atom->arg_ptr[0] = uatom->arg_ptr[0]
+ testl %eax, %eax
+ jz 20f # NULL ptr - zero out remaining args
+ cmpl $__PAGE_OFFSET, %eax # access_ok(arg_ptr)
+ jae bad_copy_uatom
+100: movl (%eax), %eax
+ movl %eax, 16(%ecx)
+
+11: movl 20(%edx), %eax # atom->arg_ptr[1] = uatom->arg_ptr[1]
+ testl %eax, %eax
+ jz 21f # NULL ptr - zero out remaining args
+ cmpl $__PAGE_OFFSET, %eax # access_ok(arg_ptr)
+ jae bad_copy_uatom
+110: movl (%eax), %eax
+ movl %eax, 20(%ecx)
+
+12: movl 24(%edx), %eax # atom->arg_ptr[2] = uatom->arg_ptr[2]
+ testl %eax, %eax
+ jz 22f # NULL ptr - zero out remaining args
+ cmpl $__PAGE_OFFSET, %eax # access_ok(arg_ptr)
+ jae bad_copy_uatom
+120: movl (%eax), %eax
+ movl %eax, 24(%ecx)
+
+13: movl 28(%edx), %eax # atom->arg_ptr[3] = uatom->arg_ptr[3]
+ testl %eax, %eax
+ jz 23f # NULL ptr - zero out remaining args
+ cmpl $__PAGE_OFFSET, %eax # access_ok(arg_ptr)
+ jae bad_copy_uatom
+130: movl (%eax), %eax
+ movl %eax, 28(%ecx)
+
+14: movl 32(%edx), %eax # atom->arg_ptr[4] = uatom->arg_ptr[4]
+ testl %eax, %eax
+ jz 24f # NULL ptr - zero out remaining args
+ cmpl $__PAGE_OFFSET, %eax # access_ok(arg_ptr)
+ jae bad_copy_uatom
+140: movl (%eax), %eax
+ movl %eax, 32(%ecx)
+
+15: movl 36(%edx), %eax # atom->arg_ptr[5] = uatom->arg_ptr[5]
+ testl %eax, %eax
+ jz 25f # NULL ptr - zero out remaining args
+ cmpl $__PAGE_OFFSET, %eax # access_ok(arg_ptr)
+ jae bad_copy_uatom
+150: movl (%eax), %eax
+ movl %eax, 36(%ecx)
+
+ xorl %eax, %eax # return 0
+ ret
+
+ #
+ # Zero out arg values. Since ptr was NULL, %eax is zero:
+ #
+20: movl %eax, 16(%ecx) # atom->args[0] = 0
+21: movl %eax, 20(%ecx) # atom->args[1] = 0
+22: movl %eax, 24(%ecx) # atom->args[2] = 0
+23: movl %eax, 28(%ecx) # atom->args[3] = 0
+24: movl %eax, 32(%ecx) # atom->args[4] = 0
+25: movl %eax, 36(%ecx) # atom->args[5] = 0
+
+ ret # return 0
+
+bad_copy_uatom:
+ movl $-14, %eax
+ ret
+
+.section __ex_table,"a"
+ .long 1b, bad_copy_uatom
+ .long 2b, bad_copy_uatom
+ .long 3b, bad_copy_uatom
+ .long 4b, bad_copy_uatom
+ .long 10b, bad_copy_uatom
+ .long 100b, bad_copy_uatom
+ .long 11b, bad_copy_uatom
+ .long 110b, bad_copy_uatom
+ .long 12b, bad_copy_uatom
+ .long 120b, bad_copy_uatom
+ .long 13b, bad_copy_uatom
+ .long 130b, bad_copy_uatom
+ .long 14b, bad_copy_uatom
+ .long 140b, bad_copy_uatom
+ .long 15b, bad_copy_uatom
+ .long 150b, bad_copy_uatom
+.previous

/*
* __get_user_X
-
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