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Line numbers in an ASM block: Unpredictable results

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  • Lance Edmonds
    replied
    I find ERADR completely acceptable, and it offers improved resolution over line numbers (per line, not per line number).


    ------------------
    Lance
    PowerBASIC Support
    mailto:[email protected][email protected]</A>

    Leave a comment:


  • Hans Ruegg
    replied
    Thank you again for your hints, although the problem seems not to be
    that easy.
    Tom, a JMP over the line number makes the number "invisible" to ERL,
    so there would be no sense in inserting the number at all.
    I tried the following code which generates a Division by Zero Error:

    Code:
    ON ERROR GOTO errHandler
    
    10 PRINT "Program Start"
    
    ! PUSH AX
    ! PUSH BX
    ! MOV AX, 3768
      ! JMP pastNumber
    20
    pastNumber:
    ! MOV BL, 0
    ! DIV BL
    ! POP BX
    ! POP AX
    
    30 PRINT "Program ends here."
    END
    
    errHandler:
    PRINT "Error "; STR$(ERR); " in Line "; STR$(ERL)
    END
    Output was: "Error 11 in Line 10"
    Without the JMP, output was (as expected): "Error 11 in Line 20".

    Maybe the conclusion is still to completely avoid line numbers in
    assembler blocks and to apply other debugging techniques?

    Regards,

    Hans Ruegg.

    Leave a comment:


  • Tom Hanlin
    replied
    If the line number is in the middle of your asm code, it may cause unexpected results.
    I'd suggest avoiding this entirely, but you may find it safe to explicitly JMP over
    line numbers.


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

    Leave a comment:


  • Lance Edmonds
    replied
    PUSH DS and SI before the line number, and POP them again afterward. However, if you jump to that line number from elsewhere, the stack frame must have those two registers PUSHed already or the stcak will be desynchronized by two unbalanced POP's.



    ------------------
    Lance
    PowerBASIC Support
    mailto:[email protected][email protected]</A>

    Leave a comment:


  • Hans Ruegg
    replied
    Thank you very much for your explanations!

    DS and SI are preserved earlier in the code, but are not restored
    before inserting the line number. So if I understand your comments
    correctly, it is possible to refer to a line number with ERL,
    provided I restore the registers before inserting the line
    number?

    Hans Ruegg

    Leave a comment:


  • Bob Zale
    replied
    One other problem with the code you posted is that you did not preserve the DS and SI registers. Perhaps you did so earlier and it's just not shown, but...

    Good luck with this.

    Bob Zale
    PowerBASIC Inc.



    ------------------

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  • Bob Zale
    replied
    1- Labels are followed by a colon, line numbers are not.

    2- When you reference ERL in a program, each occurrence of a line number must cause code to be generated to track it. It is the programmer's responsibility to ensure that the status of the machine is maintained. Don't put anything in between source code lines which may disrupt it.

    3- This is a bug in your source code, not in PowerBASIC.

    Regards,

    Bob Zale
    PowerBASIC Inc.



    ------------------

    Leave a comment:


  • Hans Ruegg
    started a topic Line numbers in an ASM block: Unpredictable results

    Line numbers in an ASM block: Unpredictable results

    This week I spent about five hours tracking a strange bug in a
    program with over 2000 lines. I had several inline assembler
    procedures which manipulate data in several arrays, and always
    the same array at the same position was overwritten with two
    bytes of data I had no idea where they came from.
    Finally I discovered by accident, that these strange two bytes,
    taken together as an integer value, corresponded exactly to the
    value of a line number I had inserted between two assembler
    statements for error tracking purposes. It looked somehow like
    this:

    Code:
    ...
    ! CLD
    ! LDS SI, CS:currentPtr    ;(this is a CS variable declared earlier)
    8020                       '(this is the line number causing the bug)
    MyLoop:
    ! LODSB
    ! XOR AH,AH
    ! TEST AL, 1
    ...
    You won't believe it: I removed the line number (8020), and everything
    worked perfectly!!

    Now this leads me to some questions, of course:

    - Is it an error to insert line numbers between assembler statements?
    - How does the compiler interpret resp. misinterpret this number?
    (I am still not able to explain how the value of the line number gets
    into a data array when the code is executed.)
    - If it is an error, why does this code compile without an error message?
    - Does it make sense at all to apply ERR and ERL to code written in
    inline Assembler? (I thought at least some errors, such as numeric
    errors or disk write errors, could be trapped like that, but maybe I am
    wrong. The program referred to makes heavy use of conventional memory,
    so I cannot run it in PBD.)

    I hope somebody can enlighten me about this point.
    Thank you!

    Hans Ruegg
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