Exceptions

[Semen Matusovski]

Today I played a little with exceptions.
I looked Florent's code, MSJ C/ASM code and some moments confused me.
1) strange values:
%ExceptionContinueExecution = 0 ...
I know that this is EXCEPTION_DISPOSITION's values valid for C except.
But why ExceptionContinueExecution <> Exception_Continue_Execution ?
Because of C implementation or something else ?
2) is it really necessary to save ESP / EBP in similar situations ?
And what happends, if do not save ?

My own test also confuses me.
Ok, first FNCLEX is possible to explain.
But why I can't avoid second FNCLEX in OnError ? (I am under Win2000).

  #Compile Exe
  #Dim All
  #Register None
  #Include "WIN32API.INC"

  '==============================================================================================
  Type EXCEPTION1_POINTERS ' <--- Because of mistake in Win32Api.Inc
     pExceptionRecord As EXCEPTION_RECORD Ptr
     pContextRecord As CONTEXT Ptr
  End Type

  Global GPFCode As Dword, GPFContAddr As Dword

  Function GPFMsg(Code As Dword) As String
     Select Case Code
        Case %EXCEPTION_ACCESS_VIOLATION      : Function = "Access violation"
        Case %EXCEPTION_DATATYPE_MISALIGNMENT : Function = "Datatype misalgnment"
        Case %EXCEPTION_BREAKPOINT            : Function = "Breakpoint"
        Case %EXCEPTION_SINGLE_STEP           : Function = "Single step"
        Case %EXCEPTION_ARRAY_BOUNDS_EXCEEDED : Function = "Array bounds exceeded"
        Case %EXCEPTION_FLT_DENORMAL_OPERAND  : Function = "Float denormal operand"
        Case %EXCEPTION_FLT_DIVIDE_BY_ZERO    : Function = "Float divide by zero"
        Case %EXCEPTION_FLT_INEXACT_RESULT    : Function = "Float inexact result"
        Case %EXCEPTION_FLT_INVALID_OPERATION : Function = "Float invalid operation"
        Case %EXCEPTION_FLT_OVERFLOW          : Function = "Float overflow"
        Case %EXCEPTION_FLT_STACK_CHECK       : Function = "Float stack check"
        Case %EXCEPTION_FLT_UNDERFLOW         : Function = "Float underflow"
        Case %EXCEPTION_INT_DIVIDE_BY_ZERO    : Function = "Integer divide by zero"
        Case %EXCEPTION_INT_OVERFLOW          : Function  = "Integer Overflow"
        Case %EXCEPTION_PRIV_INSTRUCTION      : Function = "Privileged instruction"
        Case %EXCEPTION_IN_PAGE_ERROR         : Function = "In page error"
        Case Else                             : Function  = "Exception &H" + Hex$(Code, 8)
     End Select
  End Function

  Function OurUnhandledExceptionFilter(Exception_Pointers As EXCEPTION1_POINTERS) As Long
     ! FNCLEX
     GPFCode = [email protected]
     Function =  %EXCEPTION_CONTINUE_SEARCH
     If IsFalse(VarPtr(Exception_Pointers)) Then
     ElseIf IsFalse(Exception_Pointers.pExceptionRecord) Then
     ElseIf [email protected] = %EXCEPTION_NONCONTINUABLE Then
     ElseIf IsFalse(GPFContAddr) Then
        MsgBox "You crashed the PC." + $CRLF + "Time to buy new one.", %MB_ICONEXCLAMATION, "Dr. Watson"
        Function = %EXCEPTION_EXECUTE_HANDLER
     Else
        [email protected] = GPFContAddr
        Function = %EXCEPTION_CONTINUE_EXECUTION
     End If
  End Function
  '=============================================================================
  
  Function PbMain() As Long
     Dim x As Integer, y As Integer, Stmt As Long
     SetUnhandledExceptionFilter ByVal CodePtr(OurUnhandledExceptionFilter)
     Dim s As Long
     ! FSTCW s
     s = s And &HFF30   ' Allow FPU exceptions
     ! FLDCW s

     GPFContAddr = CodePtr(OnError)
     
     
     Stmt = 1: x = 0: x = x / y

  Step2:
     Stmt = 2: x = 10: x = x / y

  Step3:
     GPFContAddr = 0

     ' Test for access violation
     Dim b As Byte Ptr
     @b = 0
    
     MsgBox "Finished" ' <-- Doesn't work, because we already exited
     Exit Function

  OnError:
     ! FNCLEX
     MsgBox GPFMsg(GPFCode) + " at statement" + Str$(Stmt), %MB_TASKMODAL, "Program Error"
     If Stmt = 1 Then GoTo Step2
     If Stmt = 2 Then GoTo Step3
  End Function

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E-MAIL: [email protected]

[Scott Turchin]

Not sure if I can help at all but when I want to *cause* one I just do this:


RaiseException %EXCEPTION_ACCESS_VIOLATION, 0, 0, 0

------------------
Scott

[Tom Hanlin]

  Type EXCEPTION1_POINTERS ' <--- Because of mistake in Win32Api.Inc

I gather that any mistake there has since been fixed. If not, please let us know.

------------------
Tom Hanlin
PowerBASIC Staff