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Assembler code for atomic_sub_64 seems wrong (i386) #5671

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Ringdingcoder opened this issue Jan 26, 2017 · 2 comments
Closed

Assembler code for atomic_sub_64 seems wrong (i386) #5671

Ringdingcoder opened this issue Jan 26, 2017 · 2 comments

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@Ringdingcoder
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While poring over the atomic code I noticed that atomic_sub_64 in lib/libspl/asm-i386/atomic.S looks wrong. Shouldn't it be subl followed by sbbl instead of adcl?
@behlendorf
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Yes, that does look wrong. @ironMann could you comment on the this.

The good news is that is the user space implementation of these atomics. They're mainly used for statistics tracking when testing ZFS in user space with ztest.

        ENTRY(atomic_sub_64)
        ALTENTRY(atomic_sub_64_nv)
        pushl   %edi
        pushl   %ebx
        movl    12(%esp), %edi
        movl    (%edi), %eax
        movl    4(%edi), %edx
1:
        movl    16(%esp), %ebx
        movl    20(%esp), %ecx
        subl    %eax, %ebx
>>>        adcl    %edx, %ecx
        lock
        cmpxchg8b (%edi)
        jne     1b
        movl    %ebx, %eax
        movl    %ecx, %edx
        popl    %ebx
        popl    %edi
        ret
        SET_SIZE(atomic_sub_64_nv)
        SET_SIZE(atomic_sub_64)

@ironMann
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Agree, that should be sbbl instead of adcl.

behlendorf added a commit to behlendorf/zfs that referenced this issue Jan 31, 2017
@behlendorf
Fix atomic_sub_64() i386 assembly implementation
2695051 
The atomic_sub_64() should use sbbl instead of adcl.  In user
space these atomics are used for statistics tracking and aren't
critical which explain how this was overlooked.  The kernel
space implementation of these atomics are layered on the
architecture specific implementations provided by the kernel.

Signed-off-by: Brian Behlendorf <[email protected]>
Issue openzfs#5671
@behlendorf behlendorf mentioned this issue Jan 31, 2017
Merged
wli5 pushed a commit to wli5/zfs that referenced this issue Feb 28, 2017
@behlendorf @wli5
Fix atomic_sub_64() i386 assembly implementation
e3e9b0e 
The atomic_sub_64() should use sbbl instead of adcl.  In user
space these atomics are used for statistics tracking and aren't
critical which explain how this was overlooked.  The kernel
space implementation of these atomics are layered on the
architecture specific implementations provided by the kernel.

Reviewed by: Stefan Ring <[email protected]>
Reviewed-by: Gvozden Neskovic <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes openzfs#5671 
Closes openzfs#5717
wli5 pushed a commit to wli5/zfs that referenced this issue Feb 28, 2017
@behlendorf @wli5
Fix atomic_sub_64() i386 assembly implementation
4fbf5f3 
The atomic_sub_64() should use sbbl instead of adcl.  In user
space these atomics are used for statistics tracking and aren't
critical which explain how this was overlooked.  The kernel
space implementation of these atomics are layered on the
architecture specific implementations provided by the kernel.

Reviewed by: Stefan Ring <[email protected]>
Reviewed-by: Gvozden Neskovic <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes openzfs#5671
Closes openzfs#5717
l1k pushed a commit to l1k/zfs that referenced this issue Apr 17, 2017
@behlendorf @l1k
Fix atomic_sub_64() i386 assembly implementation
7bdcf65 
The atomic_sub_64() should use sbbl instead of adcl.  In user
space these atomics are used for statistics tracking and aren't
critical which explain how this was overlooked.  The kernel
space implementation of these atomics are layered on the
architecture specific implementations provided by the kernel.

Reviewed by: Stefan Ring <[email protected]>
Reviewed-by: Gvozden Neskovic <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes openzfs#5671
Closes openzfs#5717
tonyhutter pushed a commit to tonyhutter/zfs that referenced this issue May 18, 2017
@behlendorf @tonyhutter
Fix atomic_sub_64() i386 assembly implementation
88d9a60 
The atomic_sub_64() should use sbbl instead of adcl.  In user
space these atomics are used for statistics tracking and aren't
critical which explain how this was overlooked.  The kernel
space implementation of these atomics are layered on the
architecture specific implementations provided by the kernel.

Reviewed by: Stefan Ring <[email protected]>
Reviewed-by: Gvozden Neskovic <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes openzfs#5671
Closes openzfs#5717
tonyhutter pushed a commit that referenced this issue Jun 9, 2017
@behlendorf @tonyhutter
Fix atomic_sub_64() i386 assembly implementation
4a4c57d 
The atomic_sub_64() should use sbbl instead of adcl.  In user
space these atomics are used for statistics tracking and aren't
critical which explain how this was overlooked.  The kernel
space implementation of these atomics are layered on the
architecture specific implementations provided by the kernel.

Reviewed by: Stefan Ring <[email protected]>
Reviewed-by: Gvozden Neskovic <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #5671
Closes #5717
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3 participants
@behlendorf @Ringdingcoder @ironMann