Windows MASM / RDTSCP

Code

.586
.MODEL FLAT,STDCALL
 include    windows.inc
 include    kernel32.inc
 includelib kernel32.lib
 include    user32.inc
 includelib user32.lib
 include    masm32.inc
 includelib masm32.lib
.data
  pat                  db 'rdtscp delta=%d, rdtsc delta=%d',13,10,0
  rdtscp_not_supported db 'rdtscp not supported'
.data?
  buf db 64 dup (?)
.code
rdtscp macro
  db 0Fh, 01h, 0F9h
endm
assume fs:nothing
RDTSCP  proc
  LOCAL _retval:DWORD
   mov  _retval,0
   pushad
   push OFFSET e
   push dword ptr fs:[0]
   mov  dword ptr fs:[0], esp
   rdtscp
   mov ebx,eax
   rdtscp
   sub  eax,ebx
   mov  _retval,eax
   jmp  no_e
 e:
   mov  esp, [esp + 8]
   pop  dword ptr fs:[0]
   add  esp, 4
   popad
   mov  _retval,-1
   jmp  _ret
 no_e:
   pop  dword ptr fs:[0]
   add  esp, 4
   popad
_ret:
   mov eax,_retval
   ret
RDTSCP  endp
  Start:
   rdtsc
   mov ebx,eax
   rdtsc
   sub  eax,ebx
   mov  ebp,eax
   call RDTSCP
   .if eax==-1
       invoke  StdOut,OFFSET rdtscp_not_supported
   .else
       invoke  wsprintfA,OFFSET buf,OFFSET pat,eax,ebp
       invoke  StdOut,OFFSET buf
   .endif
   invoke ExitProcess,0
END Start