question about InterlockedCompareExchange.

[Jack Yi]

question about InterlockedCompareExchange.
MSDN says: The function returns the initial value of the destination.
I just don't understand, why can we get the initial value of destination as
return value by 'return 0Ch' ?
Thank you!
.text:7C8097A2 ; PVOID __stdcall InterlockedCompareExchange(PVOID
*Destination,PVOID Exchange,PVOID Comperand)
.text:7C8097A2                 public _InterlockedCompareExchange@12
.text:7C8097A2 _InterlockedCompareExchange@12 proc near
.text:7C8097A2                                         ; CODE XREF:
BaseComputeProcessDllPath(x,x)+97B3p
.text:7C8097A2                                         ;
CreateActCtxW(x)+15D2Dp
.text:7C8097A2
.text:7C8097A2 Destination     = dword ptr  4
.text:7C8097A2 Exchange        = dword ptr  8
.text:7C8097A2 Comperand       = dword ptr  0Ch
.text:7C8097A2
.text:7C8097A2                 mov     ecx, [esp+Destination]
.text:7C8097A6                 mov     edx, [esp+Exchange]
.text:7C8097AA                 mov     eax, [esp+Comperand]
.text:7C8097AE
.text:7C8097AE loc_7C8097AE:                           ; DATA XREF:
.data:7C884014o
.text:7C8097AE                 lock cmpxchg [ecx], edx
.text:7C8097B2                 retn    0Ch
.text:7C8097B2 _InterlockedCompareExchange@12 endp

[Thomas Bluemel]

Learn x86 asm first... return values are returned in eax/rax
Thomas
Jack Yi wrote:
>   question about InterlockedCompareExchange.
>  MSDN says: The function returns the initial value of the destination.
>  I just don't understand, why can we get the initial value of
>  destination as return value by 'return 0Ch' ?
>  Thank you!
>  .text:7C8097A2 ; PVOID __stdcall InterlockedCompareExchange(PVOID
>  *Destination,PVOID Exchange,PVOID Comperand)
>  .text:7C8097A2                 public _InterlockedCompareExchange@12
>  <mailto:_InterlockedCompareExchange@12>
>  .text:7C8097A2 _InterlockedCompareExchange@12
>  <mailto:_InterlockedCompareExchange@12> proc near
>  .text:7C8097A2                                         ; CODE XREF:
>  BaseComputeProcessDllPath(x,x)+97B3p
>  .text:7C8097A2                                         ;
>  CreateActCtxW(x)+15D2Dp
>  .text:7C8097A2
>  .text:7C8097A2 Destination     = dword ptr  4
>  .text:7C8097A2 Exchange        = dword ptr  8
>  .text:7C8097A2 Comperand       = dword ptr  0Ch
>  .text:7C8097A2
>  .text:7C8097A2                 mov     ecx, [esp+Destination]
>  .text:7C8097A6                 mov     edx, [esp+Exchange]
>  .text:7C8097AA                 mov     eax, [esp+Comperand]
>  .text:7C8097AE
>  .text:7C8097AE loc_7C8097AE:                           ; DATA XREF:
>  .data:7C884014o
>  .text:7C8097AE                 lock cmpxchg [ecx], edx
>  .text:7C8097B2                 retn    0Ch
>  .text:7C8097B2 _InterlockedCompareExchange@12
>  <mailto:_InterlockedCompareExchange@12> endp
>  ------------------------------------------------------------------------
>  _______________________________________________
>  Ros-dev mailing list
>  Ros-dev(a)reactos.org
>  http://www.reactos.org/mailman/listinfo/ros-dev

[Alex Ionescu]

On a further note, please don't paste Windows disassembly on this
mailing list.
On 10-Oct-08, at 2:27 PM, Jack Yi wrote:
>   question about InterlockedCompareExchange.
>  MSDN says: The function returns the initial value of the destination.
>  I just don't understand, why can we get the initial value of
>  destination as return value by 'return 0Ch' ?
>  Thank you!
>  .text:7C8097A2 ; PVOID __stdcall InterlockedCompareExchange(PVOID
>  *Destination,PVOID Exchange,PVOID Comperand)
>  .text:7C8097A2                 public _InterlockedCompareExchange@12
>  .text:7C8097A2 _InterlockedCompareExchange@12 proc near
>  .text:7C8097A2                                         ; CODE XREF:
>  BaseComputeProcessDllPath(x,x)+97B3p
>  .text:7C8097A2                                         ;
>  CreateActCtxW(x)+15D2Dp
>  .text:7C8097A2
>  .text:7C8097A2 Destination     = dword ptr  4
>  .text:7C8097A2 Exchange        = dword ptr  8
>  .text:7C8097A2 Comperand       = dword ptr  0Ch
>  .text:7C8097A2
>  .text:7C8097A2                 mov     ecx, [esp+Destination]
>  .text:7C8097A6                 mov     edx, [esp+Exchange]
>  .text:7C8097AA                 mov     eax, [esp+Comperand]
>  .text:7C8097AE
>  .text:7C8097AE loc_7C8097AE:                           ; DATA
>  XREF: .data:7C884014o
>  .text:7C8097AE                 lock cmpxchg [ecx], edx
>  .text:7C8097B2                 retn    0Ch
>  .text:7C8097B2 _InterlockedCompareExchange@12 endp
>  _______________________________________________
>  Ros-dev mailing list
>  Ros-dev(a)reactos.org
>  http://www.reactos.org/mailman/listinfo/ros-dev 
Best regards,
Alex Ionescu