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Index > Macroinstructions > Minor problem with 'if.inc' macro

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madmatt



Joined: 07 Oct 2003
Posts: 1045
Location: Michigan, USA
madmatt
Hello everyone, I thought I would report a small bug with the 'if.inc' macro include, It seems to produce an extra 'jmp' right after you 'ret', before you reach the '.else' part of the macro. Is there a simple fix for this?

Code:
;[ORIGINAL CODE]
proc DDRestoreBack
     .if     dword [ddback] <> NULL
             cominvk ddback, Restore; ;this reattaches the video memory to the surface
             return
     .else
             return  -1
     .endif
endp

;[CODE DIS-ASSEMBLED WITH OBJCONV BY AGNER FOG]
        nop                                             ; 004210FD _ 90
        nop                                             ; 004210FE _ 90
        nop                                             ; 004210FF _ 90

DDRestoreBack:
        cmp     dword [?_0070], 0                       ; 00421100 _ 83. 3D, 00402248(d), 00
        jz      ?_0482                                  ; 00421107 _ 74, 0E
        mov     eax, dword [?_0070]                     ; 00421109 _ A1, 00402248(d)
        push    eax                                     ; 0042110E _ 50
        mov     eax, dword [eax]                        ; 0042110F _ 8B. 00
        call    near [eax+6CH]                          ; 00421111 _ FF. 50, 6C
        ret                                             ; 00421114 _ C3

; Note: Inaccessible code
        jmp     ?_0483                                  ; 00421115 _ EB, 06

?_0482: mov     eax, 4294967295                         ; 00421117 _ B8, FFFFFFFF
        ret                                             ; 0042111C _ C3

?_0483: nop                                             ; 0042111D _ 90
        nop                                             ; 0042111E _ 90
        nop                                             ; 0042111F _ 90
        nop                                             ; 00421120 _ 90
    

_________________
Gimme a sledge hammer! I'LL FIX IT!
Post 07 Aug 2010, 23:06
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
I think that detecting whether the jmp that skips the else (or elseIf) block is required or not is too hard even if considering ret alone only. For instance, I think you won't find a method to detect situations like this:

Code:
proc foo, arg
  .if dword [arg] <> NULL
    call [arg]
    test eax, eax
    js @f
    return
@@:
  .else
    return -1
  .endif
  
  return -2
endp    
This clearly kill the naive method of detecting if the last instruction in the If/ElseIf body was a RET to perform JMP suppression. If we assume that there are no jumps from nowhere into any part of the body nor intra-body jumps, the naive method is still a problem:

Code:
proc foo, arg
  .if dword [arg] <> NULL
    call [arg]
    .if eax >= 0
      return
    .endif
@@:
  .else
    return -1
  .endif
  
  return -2
endp    
But perhaps correctly detecting when the JMP to skip the else is needed is doable with fasm, the other one I think it is impossible to get it right.
Post 08 Aug 2010, 00:36
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madmatt



Joined: 07 Oct 2003
Posts: 1045
Location: Michigan, USA
madmatt
Quote:
But perhaps correctly detecting when the JMP to skip the else is needed is doable with fasm, the other one I think it is impossible to get it right.


I was thinking something like having something like '.else NJ' (NJ = no jmp) to signal that a 'jmp' shouldn't be used when the .else macro keyword is used.
Post 08 Aug 2010, 13:05
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Tomasz Grysztar
Assembly Artist


Joined: 16 Jun 2003
Posts: 7715
Location: Kraków, Poland
Tomasz Grysztar
madmatt wrote:
I was thinking something like having something like '.else NJ' (NJ = no jmp) to signal that a 'jmp' shouldn't be used when the .else macro keyword is used.
Isn't it better to just write it this way?
Code:
     .if     dword [ddback] <> NULL 
             cominvk ddback, Restore; ;this reattaches the video memory to the surface 
             return 
     .endif 
             return  -1     
Post 08 Aug 2010, 13:23
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madmatt



Joined: 07 Oct 2003
Posts: 1045
Location: Michigan, USA
madmatt
Tomasz Grysztar wrote:
madmatt wrote:
I was thinking something like having something like '.else NJ' (NJ = no jmp) to signal that a 'jmp' shouldn't be used when the .else macro keyword is used.
Isn't it better to just write it this way?
Code:
     .if     dword [ddback] <> NULL 
             cominvk ddback, Restore; ;this reattaches the video memory to the surface 
             return 
     .endif 
             return  -1     


Yeh, that would work better. But, still seems to need a fix when it is inserting code that is not needed (obviously, this should be a very low priority fix, nothing is truly broken here.). By the way, also discovered that the '.elseif' macro does the same thing. see code below.
Code:
;[ORIGINAL CODE]
proc DDGetDefaultFont  fontaddress, fontnumber
     .if     [fontnumber] = DDCHARFONTVGA8
             cinvoke memcpy, [fontaddress], vgafont8x8, 2048
             return  DD_OK

     .elseif [fontnumber] = DDCHARFONTATR8
             cinvoke memcpy, [fontaddress], atarifont8x8, 2048
             return  DD_OK

     .elseif [fontnumber] = DDCHARFONTAPP8
             cinvoke memcpy, [fontaddress], AppleFont8x8, 2048
             return  DD_OK

     .elseif [fontnumber] = DDCHARFONTC648
             cinvoke memcpy, [fontaddress], c64font8x8, 4096
             return  DD_OK

     .elseif [fontnumber] = DDCHARFONTVGA16
             cinvoke memcpy, [fontaddress], vgafont8x16, 4096
             return  DD_OK
     .else 1
             return -1
     .endif
endp

;[CODE DIS-ASSEMBLED WITH OBJCONV BY AGNER FOG]
        nop                                             ; 00423D7A _ 90
        nop                                             ; 00423D7B _ 90
        nop                                             ; 00423D7C _ 90
        nop                                             ; 00423D7D _ 90
        nop                                             ; 00423D7E _ 90
        nop                                             ; 00423D7F _ 90

DDGetDefaultFont:; Function begin
        push    ebp                                     ; 00423D80 _ 55
        mov     ebp, esp                                ; 00423D81 _ 89. E5
        cmp     dword [ebp+0CH], 0                      ; 00423D83 _ 83. 7D, 0C, 00
        jnz     ?_0716                                  ; 00423D87 _ 75, 24
        push    2048                                    ; 00423D89 _ 68, 00000800
        push    ?_0145                                  ; 00423D8E _ 68, 004029C0(d)
        push    dword [ebp+8H]                          ; 00423D93 _ FF. 75, 08
        call    near [imp_memcpy]                       ; 00423D96 _ FF. 15, 00429516(d)
        add     esp, 12                                 ; 00423D9C _ 83. C4, 0C
        mov     eax, 0                                  ; 00423D9F _ B8, 00000000
        leave                                           ; 00423DA4 _ C9
        ret     8                                       ; 00423DA5 _ C2, 0008

; Note: Inaccessible code
        jmp     ?_0721                                  ; 00423DA8 _ E9, 000000A3

?_0716: cmp     dword [ebp+0CH], 1                      ; 00423DAD _ 83. 7D, 0C, 01
        jnz     ?_0717                                  ; 00423DB1 _ 75, 21
        push    2048                                    ; 00423DB3 _ 68, 00000800
        push    ?_0148                                  ; 00423DB8 _ 68, 004051C0(d)
        push    dword [ebp+8H]                          ; 00423DBD _ FF. 75, 08
        call    near [imp_memcpy]                       ; 00423DC0 _ FF. 15, 00429516(d)
        add     esp, 12                                 ; 00423DC6 _ 83. C4, 0C
        mov     eax, 0                                  ; 00423DC9 _ B8, 00000000
        leave                                           ; 00423DCE _ C9
        ret     8                                       ; 00423DCF _ C2, 0008

; Note: Inaccessible code
        jmp     ?_0721                                  ; 00423DD2 _ EB, 7C

?_0717: cmp     dword [ebp+0CH], 2                      ; 00423DD4 _ 83. 7D, 0C, 02
        jnz     ?_0718                                  ; 00423DD8 _ 75, 21
        push    2048                                    ; 00423DDA _ 68, 00000800
        push    ?_0149                                  ; 00423DDF _ 68, 004059C0(d)
        push    dword [ebp+8H]                          ; 00423DE4 _ FF. 75, 08
        call    near [imp_memcpy]                       ; 00423DE7 _ FF. 15, 00429516(d)
        add     esp, 12                                 ; 00423DED _ 83. C4, 0C
        mov     eax, 0                                  ; 00423DF0 _ B8, 00000000
        leave                                           ; 00423DF5 _ C9
        ret     8                                       ; 00423DF6 _ C2, 0008

; Note: Inaccessible code
        jmp     ?_0721                                  ; 00423DF9 _ EB, 55

?_0718: cmp     dword [ebp+0CH], 3                      ; 00423DFB _ 83. 7D, 0C, 03
        jnz     ?_0719                                  ; 00423DFF _ 75, 21
        push    4096                                    ; 00423E01 _ 68, 00001000
        push    ?_0147                                  ; 00423E06 _ 68, 004041C0(d)
        push    dword [ebp+8H]                          ; 00423E0B _ FF. 75, 08
        call    near [imp_memcpy]                       ; 00423E0E _ FF. 15, 00429516(d)
        add     esp, 12                                 ; 00423E14 _ 83. C4, 0C
        mov     eax, 0                                  ; 00423E17 _ B8, 00000000
        leave                                           ; 00423E1C _ C9
        ret     8                                       ; 00423E1D _ C2, 0008

; Note: Inaccessible code
        jmp     ?_0721                                  ; 00423E20 _ EB, 2E

?_0719: cmp     dword [ebp+0CH], 4                      ; 00423E22 _ 83. 7D, 0C, 04
        jnz     ?_0720                                  ; 00423E26 _ 75, 1F
        push    4096                                    ; 00423E28 _ 68, 00001000
        push    ?_0146                                  ; 00423E2D _ 68, 004031C0(d)
        push    dword [ebp+8H]                          ; 00423E32 _ FF. 75, 08
        call    near [imp_memcpy]                       ; 00423E35 _ FF. 15, 00429516(d)
        add     esp, 12                                 ; 00423E3B _ 83. C4, 0C
        mov     eax, 0                                  ; 00423E3E _ B8, 00000000
        leave                                           ; 00423E43 _ C9
        ret     8                                       ; 00423E44 _ C2, 0008

?_0720: mov     eax, 4294967295                         ; 00423E47 _ B8, FFFFFFFF
        leave                                           ; 00423E4C _ C9
        ret     8                                       ; 00423E4D _ C2, 0008

?_0721: nop                                             ; 00423E50 _ 90
        nop                                             ; 00423E51 _ 90
        nop                                             ; 00423E52 _ 90
        nop                                             ; 00423E53 _ 90
        nop                                             ; 00423E54 _ 90
        nop                                             ; 00423E55 _ 90
        nop                                             ; 00423E56 _ 90
        nop                                             ; 00423E57 _ 90
        nop                                             ; 00423E58 _ 90
        nop                                             ; 00423E59 _ 90
    

_________________
Gimme a sledge hammer! I'LL FIX IT!
Post 08 Aug 2010, 17:49
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