[PATCH] x86_64: Clean up copy_*_user
- Remove optimization for old B stepping Opteron - Make the fast path for copies with a multiple of eight length faster. - Minor instruction rearrangement to hopefully avoid a pipeline stall or two. - Add comment about errata to consider. Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Andi Kleen
Linus Torvalds
parent
17a941d854
commit
2cbc9ee35c
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@ -4,12 +4,9 @@
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* Functions to copy from and to user space.
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*/
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#define FIX_ALIGNMENT 1
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#include <asm/current.h>
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#include <asm/asm-offsets.h>
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#include <asm/thread_info.h>
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#include <asm/cpufeature.h>
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/* Standard copy_to_user with segment limit checking */
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.globl copy_to_user
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@ -21,23 +18,7 @@ copy_to_user:
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jc bad_to_user
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cmpq threadinfo_addr_limit(%rax),%rcx
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jae bad_to_user
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2:
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.byte 0xe9 /* 32bit jump */
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.long .Lcug-1f
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1:
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.section .altinstr_replacement,"ax"
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3: .byte 0xe9 /* replacement jmp with 8 bit immediate */
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.long copy_user_generic_c-1b /* offset */
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.previous
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.section .altinstructions,"a"
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.align 8
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.quad 2b
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.quad 3b
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.byte X86_FEATURE_K8_C
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.byte 5
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.byte 5
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.previous
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jmp copy_user_generic
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/* Standard copy_from_user with segment limit checking */
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.globl copy_from_user
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@ -72,223 +53,44 @@ bad_to_user:
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* rsi source
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* rdx count
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*
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* Only 4GB of copy is supported. This shouldn't be a problem
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* because the kernel normally only writes from/to page sized chunks
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* even if user space passed a longer buffer.
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* And more would be dangerous because both Intel and AMD have
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* errata with rep movsq > 4GB. If someone feels the need to fix
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* this please consider this.
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*
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* Output:
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* eax uncopied bytes or 0 if successful.
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*/
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.globl copy_user_generic
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.p2align 4
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copy_user_generic:
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.byte 0x66,0x66,0x90 /* 5 byte nop for replacement jump */
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.byte 0x66,0x90
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1:
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.section .altinstr_replacement,"ax"
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2: .byte 0xe9 /* near jump with 32bit immediate */
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.long copy_user_generic_c-1b /* offset */
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.previous
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.section .altinstructions,"a"
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.align 8
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.quad copy_user_generic
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.quad 2b
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.byte X86_FEATURE_K8_C
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.byte 5
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.byte 5
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.previous
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.Lcug:
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pushq %rbx
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xorl %eax,%eax /*zero for the exception handler */
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#ifdef FIX_ALIGNMENT
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/* check for bad alignment of destination */
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movl %edi,%ecx
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andl $7,%ecx
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jnz .Lbad_alignment
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.Lafter_bad_alignment:
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#endif
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movq %rdx,%rcx
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movl $64,%ebx
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shrq $6,%rdx
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decq %rdx
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js .Lhandle_tail
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.p2align 4
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.Lloop:
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.Ls1: movq (%rsi),%r11
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.Ls2: movq 1*8(%rsi),%r8
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.Ls3: movq 2*8(%rsi),%r9
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.Ls4: movq 3*8(%rsi),%r10
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.Ld1: movq %r11,(%rdi)
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.Ld2: movq %r8,1*8(%rdi)
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.Ld3: movq %r9,2*8(%rdi)
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.Ld4: movq %r10,3*8(%rdi)
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.Ls5: movq 4*8(%rsi),%r11
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.Ls6: movq 5*8(%rsi),%r8
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.Ls7: movq 6*8(%rsi),%r9
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.Ls8: movq 7*8(%rsi),%r10
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.Ld5: movq %r11,4*8(%rdi)
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.Ld6: movq %r8,5*8(%rdi)
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.Ld7: movq %r9,6*8(%rdi)
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.Ld8: movq %r10,7*8(%rdi)
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decq %rdx
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leaq 64(%rsi),%rsi
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leaq 64(%rdi),%rdi
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jns .Lloop
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.p2align 4
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.Lhandle_tail:
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movl %ecx,%edx
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andl $63,%ecx
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shrl $3,%ecx
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jz .Lhandle_7
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movl $8,%ebx
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.p2align 4
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.Lloop_8:
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.Ls9: movq (%rsi),%r8
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.Ld9: movq %r8,(%rdi)
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decl %ecx
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leaq 8(%rdi),%rdi
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leaq 8(%rsi),%rsi
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jnz .Lloop_8
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.Lhandle_7:
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movl %edx,%ecx
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andl $7,%ecx
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jz .Lende
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.p2align 4
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.Lloop_1:
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.Ls10: movb (%rsi),%bl
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.Ld10: movb %bl,(%rdi)
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incq %rdi
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incq %rsi
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decl %ecx
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jnz .Lloop_1
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.Lende:
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popq %rbx
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ret
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#ifdef FIX_ALIGNMENT
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/* align destination */
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.p2align 4
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.Lbad_alignment:
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movl $8,%r9d
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subl %ecx,%r9d
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movl %r9d,%ecx
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cmpq %r9,%rdx
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jz .Lhandle_7
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js .Lhandle_7
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.Lalign_1:
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.Ls11: movb (%rsi),%bl
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.Ld11: movb %bl,(%rdi)
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incq %rsi
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incq %rdi
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decl %ecx
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jnz .Lalign_1
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subq %r9,%rdx
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jmp .Lafter_bad_alignment
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#endif
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/* table sorted by exception address */
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.section __ex_table,"a"
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.align 8
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.quad .Ls1,.Ls1e
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.quad .Ls2,.Ls2e
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.quad .Ls3,.Ls3e
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.quad .Ls4,.Ls4e
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.quad .Ld1,.Ls1e
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.quad .Ld2,.Ls2e
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.quad .Ld3,.Ls3e
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.quad .Ld4,.Ls4e
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.quad .Ls5,.Ls5e
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.quad .Ls6,.Ls6e
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.quad .Ls7,.Ls7e
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.quad .Ls8,.Ls8e
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.quad .Ld5,.Ls5e
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.quad .Ld6,.Ls6e
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.quad .Ld7,.Ls7e
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.quad .Ld8,.Ls8e
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.quad .Ls9,.Le_quad
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.quad .Ld9,.Le_quad
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.quad .Ls10,.Le_byte
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.quad .Ld10,.Le_byte
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#ifdef FIX_ALIGNMENT
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.quad .Ls11,.Lzero_rest
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.quad .Ld11,.Lzero_rest
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#endif
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.quad .Le5,.Le_zero
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.previous
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/* compute 64-offset for main loop. 8 bytes accuracy with error on the
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pessimistic side. this is gross. it would be better to fix the
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interface. */
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/* eax: zero, ebx: 64 */
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.Ls1e: addl $8,%eax
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.Ls2e: addl $8,%eax
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.Ls3e: addl $8,%eax
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.Ls4e: addl $8,%eax
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.Ls5e: addl $8,%eax
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.Ls6e: addl $8,%eax
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.Ls7e: addl $8,%eax
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.Ls8e: addl $8,%eax
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addq %rbx,%rdi /* +64 */
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subq %rax,%rdi /* correct destination with computed offset */
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shlq $6,%rdx /* loop counter * 64 (stride length) */
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addq %rax,%rdx /* add offset to loopcnt */
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andl $63,%ecx /* remaining bytes */
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addq %rcx,%rdx /* add them */
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jmp .Lzero_rest
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/* exception on quad word loop in tail handling */
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/* ecx: loopcnt/8, %edx: length, rdi: correct */
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.Le_quad:
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shll $3,%ecx
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andl $7,%edx
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addl %ecx,%edx
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/* edx: bytes to zero, rdi: dest, eax:zero */
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.Lzero_rest:
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movq %rdx,%rcx
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.Le_byte:
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xorl %eax,%eax
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.Le5: rep
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stosb
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/* when there is another exception while zeroing the rest just return */
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.Le_zero:
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movq %rdx,%rax
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jmp .Lende
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/* C stepping K8 run faster using the string copy instructions.
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This is also a lot simpler. Use them when possible.
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Patch in jmps to this code instead of copying it fully
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to avoid unwanted aliasing in the exception tables. */
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/* rdi destination
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* rsi source
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* rdx count
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*
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* Output:
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* eax uncopied bytes or 0 if successfull.
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*/
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copy_user_generic_c:
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movl %edx,%ecx
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shrl $3,%ecx
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andl $7,%edx
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jz 5f
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1: rep
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movsq
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movl %edx,%ecx
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xor %eax,%eax
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2: rep
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movsb
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4: movl %ecx,%eax
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ret
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/* align here? */
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5: xorl %eax,%eax
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6: rep movsq
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ret
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.section .fixup,"ax"
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3: lea (%rdx,%rcx,8),%rax
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ret
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4: movl %ecx,%eax
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ret
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.previous
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.section __ex_table,"a"
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.quad 1b,3b
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.quad 2b,4b
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.quad 6b,4b
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.previous
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