[Android, 32-Bit, Debug] Projekt raised exception class Bus error (10)

[Rollo62 546]

Hi there,

 

I've got a strange exception, only with Android 32-Bit during Debugging, other platforms including IOS work well.
With iOS 64 I had no issue seen, but wouldn't count on it right now.

 

I use a TDateTime variable,  and want to compare against NULL..

Since TDateTime is a Double with 8 Bytes, a simple cast to Double( Self ) should make not any harm.

Maybe there are special conditions on Android, as Extended is reduced to Double, and maybe there are some conversion side effects with Double as well ?

 

 

I use a class helper for adding such functionality, which is used in a million other places too.

function  TDateTime_Helper.ToDouble : Double;
begin
    Result := Double( Self );  // Here it crashes, see images enclosed, they only have 2 ARM assembler lines
end;

and I already extended my conversion routing to separated local variables:

// global variable for storage, only reading
var
    LUNull     : TDateTime = TDateTime( 0.0 );  


class function TDateTime_Helper.Create_Null : TDateTime;
begin
    Result := LUNull;  // Could the global variable cause issues in a Thread ?  Buts its readonly.
end;


function TDateTime_Helper.IsNull : Boolean;
var
    LSelf : Double;
    LNull : Double;
begin
    LSelf := Self.ToDouble;         //11.03.20 added local variables, to check Android crash
    LNull := Create_Null.ToDouble;

    if SameValue( LSelf, LNull ) then
        Result := True
    else
        Result := False;
end;

I check a variable, which is called in a thread

if FLastUpdate.IsNull then  // called like this
begin
   ....
end

 

I must confess that I use above scheme in many thousands of places, also heavily within threads (even higher loded),  without an error before.

• The caller can be debugged very reliable, and the error is very reproducable
• When the caller comes in first, second, third time, with zero, all is fine
• When the caller comes in with a real Double value, I can debug and see a valid double value in the watch (e.g. FLastUpdate = 43901.1603147338 )
• Inside the conversion ToDouble it crashes

 

When entering with Zero, it looks like the images img. 1 and 2  (see the registers changing)

When entering with Date, it looks like img. 3, and immediately it crashes at img. 4

 

What could cause such error, it sounds a little like failure of JNI Bus, but maybe I'M totally on the wrong track ?

Probably there is some genius with a good hint how to fix this nasty bug.

 

 

 

 

 

 

 

Edited March 11, 2020 by Rollo62

[Rollo62 546]

I just tired a brute-force approach to get this solved.

I replaced this

function  TDateTime_Helper.ToDouble  : Double;
begin
    Result := Double( Self );
end;

by that

function  TDateTime_Helper.ToDouble  : Double;
var
    LDbl : Double;

begin
    Move( Self, LDbl, Sizeof( LDbl) );

    Result := LDbl;
end;

And believe it or not, I have a crash-less app now.

 

Any ideas or explanations ?

I still would like to get back to the original approach, which should be more effective (untested).

 

 

 

 

 

Edited March 11, 2020 by Rollo62