Better code check before compile?


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  1. #1
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    Default Better code check before compile?

    Hello. Recently accidentially deleted RETURN in one subroutine, and it caused catastrophic failure to attached hardware (almost started a fire). Of course this is my fault, but even on ZX Spectrum we had "gosub without return" error check. So I guess, it'll be nice if this will be implemented in PBP. It does that check for FOR-NEXT, why it can't be done for GOSUB-RETURN?

  2. #2
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    Default Re: Better code check before compile?

    I don't write compilers and/or preprocessors but from my limited point of view I can't really see how a check like that would work in the case of PBP. How would the compiler or preprocessor be able to "match" a RETURN statement with a GOSUB?

    You can easily have several RETURN statements and multiple labels within a single subroutine.

    Alright, if there's one (or more) GOSUB statements in the program but not a single RETURN statement you know you have a problem but apart from that I'm not sure how it would work.

    In your case I suppose the following represents what happened, the RETURN from Label1 got deleted and is missing but that isn't NECCESARILY an error, the code is still correct.
    Code:
    Label1:
      ...code
      ...clode
    
    Label2:
      ...code
      ...code
    RETURN
    Out of curiosity, would you share more details about what happened?

    /Henrik.

  3. #3
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    Default Re: Better code check before compile?

    How would the compiler or preprocessor be able to "match" a RETURN statement with a GOSUB?
    Hi,

    As one RETURN statement can match more than one GOSUB's ...

    even math can't do anything for you ... just verify if there's at least one RETURN for one GOSUB ...or number of RETURN is smaller or equal than number of GOSUB

    the only way is to run the debugger and verify you jump at the good moment or to the right location ...

    for critical applications, only a GOTO - GOTO or multiple local subroutine INCLUDE could secure the code ...

    but you also could wipe the critical line ...



    Alain
    Last edited by Acetronics2; - 26th December 2019 at 13:03.
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  4. #4
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    Default Re: Better code check before compile?

    If your code can start fire, you are doing something really wrong.
    For first run, always use PSU with limited power(at least current limiting) with no load at output. Move actuators if you have them manually to check sensors.
    If you are creating PSU controlled by PIC(or any mcu), simulate output voltage by applying voltage on feedback.
    Any way you must have HW protections that would prevent code to do catastrophic damage.

    As all software in this world PBP can have unsuspected bugs that doesn't manifest all time. I found one few years ago. Other compilers have many more than one.
    Also as this is all clock dependent, it can freeze due falling oscillator eg lot of vibration can cause crystal to breaks.

    I saw result of using PLC with untested code on 300ton press, and actuating pressing and pulling actuators, it wasn't pretty... And that could be avoided if hydraulics was done correctly to disallow engaging both actuators in opposite directions. Or using relay that would disable inputs to other solenoids, etc...

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    Default Re: Better code check before compile?

    Added to the above, no one can guarantee you that the software will always run, even with faults in it. MCU's can stop anytime and hardware must protect itself in that case.

    Now, regarding Subs, it is not easy or feasible at all, to check for correct pairs of gosub-return. It is not the same as open-close of { and } in C for example.

    In the case of Returns, you can have one or 100 for the same sub. So, how will the compiler check?

    Ioannis

  6. #6
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    Default Re: Better code check before compile?

    it is simple. Just count number of Subroutines and RETURNs and make sure they match, that's all, and already done 30 years ago.

    Regarding what happened - it was huge (about 30 meters) Christmas tree 8 channel light controller. The code enables lights at max power for 0.1 second, to give "blink" effect. It worked for 2 years without any issues, until now, when I added some new programs, and forgot to add RETURN, so lights remain at high power for about 10 minutes, instead of 0.5second. It ended up with 9 pieces of solid state relays fried, until thermal switch cut off the power
    Last edited by CuriousOne; - 26th December 2019 at 15:33.

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    Default Re: Better code check before compile?

    Even more simple.

    Just add different label for subroutines, say, subroutines should start with SUB statement, after the label. At compile time, do check and that's all.

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    Default Re: Better code check before compile?

    Then 80% of my programs wouldn't compile. I often use multiple entry point in same sub. And have only one return at end.

  9. #9
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    Default Re: Better code check before compile?

    Or the reverse. Have one entry and multiple exits:

    Code:
    gosub test
    
    ....
    
    test:
    if x=1 then
       a=1
       return
    endif
    
    if x=2 then
       a=2
       return
    endif
    
    return
    Ioannis

  10. #10
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    Default Re: Better code check before compile?

    So you're doing it wrong - same for overlapping for-next cycles

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    Default Re: Better code check before compile?

    If you mean my example, OK, it is a not efficient one but I was trying to show that you can have many Returns from the same sub.

    Sure it can be made more compact or efficient, but still. Compiler has difficult time to check this for errors.

    Ioannis

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    Default Re: Better code check before compile?

    Ok, here is an example (not exact syntax, just to get idea)

    Code:
    MAINCODE: 'do something
    high PORTC.0
    PAUSE 500
    low PORTC.0
    Pause 500
    GOSUB CHECKER
    GOTO MAINCODE
    CHECKER:
    TOGGLE PORTD.0
    RETURN
    In above example, if we remove RETURN, it will compile fine in PBP, but will produce unusable code. But even on ZX Spectrum, it would give us "Gosub without return" error, and save our time.

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    Default Re: Better code check before compile?

    Agreed. This is easy to check, but above we stated other cases that are difficult to check.

    So a sub-without-return check in whole is not easy to implement. I suppose... Maybe Charles knows better to justify it.

    Ioannis

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    Default Re: Better code check before compile?

    There have been situations where if a test meets certain criteria you want to go through 5 sequences of code. However, if one of the criteria is missing, you want to skip the first sequence and do the other 4. On down the line, you may only need to do the last 2. The subroutine may look like;
    Code:
    Main:
    SELECT CASE Var
     CASE < 50 : GOSUB Sub1
     CASE < 100 : GOSUB Sub2
     CASE < 150 : GOSUB Sub3
     CASE < 200 : GOSUB Sub4
     CASE ELSE : GOSUB Sub5
    END SELECT
    GOTO Main
    
    Sub5:
     TOGGLE LED1
    Sub4:
     TOGGLE LED2
    Sub3:
     TOGGLE LED3
    Sub2:
     HIGH LATA.4
    Sub1:
     LATB = 0
    RETURN
    Here is a legitimate case of needing only 1 RETURN for multiple subroutines.

  15. #15
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    Default Re: Better code check before compile?

    That is exactly what I have on my mind in post #8.
    Maybe it will be useful if compiler give just warning about missing RETUN.
    But That wouldn't prevent bad stuff from happening same as it throwing an error wouldn't prevent that. So no real point of having it.

  16. #16
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    Default Re: Better code check before compile?

    Another "bug" found - you can easily refer to out of array bounds and it won't give any error during compile
    like

    MAS var byte[5]
    MAS[10]=20

    Won't give any error or warning.

  17. #17
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    Default Re: Better code check before compile?

    You may have found something you did not know and it IS something to be aware of but it's not a bug. It's like that by design.
    It's all covered in details thru out section 7.6 in the manual - read it ;-)

    /Henrik.

  18. #18
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    Default Re: Better code check before compile?

    It is common to other languages too like C for example.

    Ioannis

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    Default Re: Better code check before compile?

    And the compiler is really only able (if so designed) to catch out-of-bounds error when you have a static index like that MAS[10]=20 but in many cases you're using an index variable like MAS[x]=20 and then there is no way for the compiler to know what x is going to be at runtime.

    On your typical 80's computer running BASIC, like the ZX Spectrum referenced earlier, the execution was interpreted so the interpreter could catch out of bounds errors during execution. PBP isn't interpreted but say it was or that it in some other way COULD detect that out-of-bounds error - what should happen?
    Last edited by HenrikOlsson; - 2nd November 2020 at 11:37.

  20. #20
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    Default Re: Better code check before compile?

    Yes the example I have is static, not runtime occurrence.

  21. #21
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    Default Re: Better code check before compile?


    Found another "bug" - if you put more DATA lines in code, than size of built-in eeprom, it will compile without errors, but PicKit 3 programmer will show you "Warning: Hex file loaded is larger than device."

  22. #22
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    Default Re: Better code check before compile?

    Interesting... This is easy to check I guess.

    Ioannis

  23. #23
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    Default Re: Better code check before compile?

    I made a typo, putting = instead of -

    hpwm 2,rmd*rmd=1,20000

    This statement does not produce any errors, as it should. Also, RMD value remains the same

  24. #24
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    Default Re: Better code check before compile?

    Found another.

    Here is sample code, both variants should work same, but they don't

    Code:
    if ticker>150 and ard<140 and atrig=0 then
    ticker=1 
    atrig=1 
    endif
    This one is fine, but this one:
    Code:
    if ticker>150 and ard<140 and atrig=0 then ticker=1: atrig=1
    is not - atrig is always set to 1, no matter if ticker and ard values are as defined in if-then thing. It looks like that code after : is handled as separate code, not part of if-then. But, if I add say GOSUB XX after it, it is executed.

  25. #25
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    Default Re: Better code check before compile?

    That is not bug. That way should work. This : is same as new row.
    So this line
    Code:
    if ticker>150 and ard<140 and atrig=0 then ticker=1: atrig=1
    is same as this

    Code:
    if ticker>150 and ard<140 and atrig=0 then ticker=1
    
    atrig=1
    I'm using PBP since 2004. And I found only one bug in pbp, and encounter multiple in MPASM.... DT helped me a lot to track bug to MPASM...

  26. #26
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    Default Re: Better code check before compile?

    no, it is not, because if I add GOSUB statement, it is being triggered on IF-THEN condition only.

  27. #27
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    Default Re: Better code check before compile?

    Hehe. Read manual...
    This : replaces new row. Same as you press enter on your keyboard. So try to compile code from my code above. You will get same results.
    Only thing behind THEN depending on IF. Next statement after : does not.

  28. #28
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    Default Re: Better code check before compile?

    From manual
    Code:
    2.18 Line-Concatenation ( : )
    Multiple commands may be written on a single line using colon characters to tell PBP where to insert a "virtual" line break.

  29. #29
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    Default Re: Better code check before compile?

    I agree with peja089, the colon acts as a virtual line break.
    If more than a signle statement should execute as a result of the evaluation use IF-THEN-ENDIF.

    With that said... In section 5.35 of the manual they actually DO show the following as a valid example:
    Code:
    IF B0 <> 10 THEN B0 = B0 + 1: B1 = B1 - 1
    And in fact, when compiling the followong code for a 16F628 both the Test1 and Test2 routines results in the same assembly code
    Code:
    A VAR BYTE
    B VAR BYTE
    C VAR BYTE
    D VAR BYTE
    
    Test1:
    IF A = 12 THEN B = 2 : C = 3 :  D = 4
    
    Test2:
    IF A = 12 THEN
      B=2
      C=3
      D=4
    ENDIF
    Here's the resulting assembly (both versions looks identical to me (wasn't really expecting that to be honest):
    Code:
    _Test1
             clrwdt
             movf    _A,  W
             sublw   00Ch
             btfss   STATUS, Z
             goto    L00001
             movlw   low (002h)
             movwf   _B
             movlw   low (003h)
             movwf   _C
             movlw   low (004h)
             movwf   _D
    L00001
    _Test2
            clrwdt
            movf    _A,  W
            sublw   00Ch
            btfss   STATUS, Z
            goto    L00003
            movlw   low (002h)
            movwf   _B
            movlw   low (003h)
            movwf   _C
            movlw   low (004h)
            movwf   _D
    L00003
    That got me curious so I compiled both version of the original code
    Code:
    ticker VAR BYTE
    ard VAR BYTE
    atrig VAR BYTE
    
    Test1:
    if ticker>150 and ard<140 and atrig=0 then ticker=1: atrig=1
    
    Test2:
    if ticker>150 and ard<140 and atrig=0 then
      ticker=1
      atrig=1
    ENDIF
    And the resulting assebly (less library code) looks like this:
    Code:
    _Test1
            movf    _ticker, W
            movwf   R0
            movlw   low (096h)
            call    CMPGTB
            movwf   T1
            movf    _ard, W
            movwf   R0
            movlw   low (08Ch)
            call    CMPLTB
            movwf   T2
            movf    T1,  W
            movwf   FSR
            movf    T2,  W
            call    LAND
            movwf   T2
            movwf   T2   + 1
            movf    _atrig, W
            sublw   000h
            btfss   STATUS, Z
            movlw   -1
            xorlw   0ffh
            movwf   T3
            movf    T2,  W
            iorwf   T2  + 1, W
            movwf   FSR
            movf    T3,  W
            call    LAND
            movwf   T3
            movwf   T3   + 1
            clrwdt
            movf    T3,  W
            iorwf   (T3)  + 1, W
            btfsc   STATUS, Z
            goto    L00001
            movlw   low (001h)
            movwf   _ticker
            movlw   low (001h)
            movwf   _atrig
    L00001
    _Test2
            movf    _ticker, W
            movwf   R0
            movlw   low (096h)
            call    CMPGTB
            movwf   T1
            movf    _ard, W
            movwf   R0
            movlw   low (08Ch)
            call    CMPLTB
            movwf   T2
            movf    T1,  W
            movwf   FSR
            movf    T2,  W
            call    LAND
            movwf   T2
            movwf   T2   + 1
            movf    _atrig, W
            sublw   000h
            btfss   STATUS, Z
            movlw   -1
            xorlw   0ffh
            movwf   T3
            movf    T2,  W
            iorwf   T2  + 1, W
            movwf   FSR
            movf    T3,  W
            call    LAND
            movwf   T3
            movwf   T3   + 1
            clrwdt
            movf    T3,  W
            iorwf   (T3)  + 1, W
            btfsc   STATUS, Z
            goto    L00003
            movlw   low (001h)
            movwf   _ticker
            movlw   low (001h)
            movwf   _atrig
    L00003
    As far as I can see they are identical, meaning atrig will only get set to 1 if the evaulation is true. So I don't know what might be happening in CuriousOnes case because as far as I can see it IS working as CuriousOne expects - which I did NOT expect.

    /Henrik.

  30. #30
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    Default Re: Better code check before compile?

    Quote Originally Posted by HenrikOlsson View Post
    ... which I did NOT expect.
    /Henrik.
    Same here

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