What can cause System.Move to occasionaly give wrong results?
- by Fredrik Loftheim
The last few days we have had some strange problems with our database components developed by a third party. There has been no changes to these components for months.
The code that HAS changed the last few days is our own code and we have also updated our gui-components developed by another third party.
After debugging I have found that a call to System.Move in one of the database component procedures occationaly gives wrong results!
Please take a look at the code below from the database components and read my comments. How can this inconsistent behaviour happen?
Can anyone give me an idea of how to procede to find the cause of this inconsistent behaviour?
NB! I dont think there is anything wrong with THIS code, it is only shown to explain the problem "symptoms".
My guess is that there is some sort of memory corruption or something, caused by our code or the updated gui-component-code.
Edit: Take a look at the blogpost linked below. It seems that it could be related to my problem. At least as I read it it confirms that System.Move can give wrong results:
http://blog.excastle.com/2007/08/28/delphi-bug-of-the-day-fpu-stack-leak/
Procedure InternalDescribe;
var
cbufl: sb4; //sb4=LongInt
cbuf: array[0..30] of char;
cbufp: PChar;
//....
begin
//..Some code
repeat
//...Some code to initialize cbufp and cbufl
//On the 15. iteration the values immediately Before Move are always these:
//cbufp = 'STDPRODUCTSTOREDELEMENTSCOUNT'
//cbuf = ('S', 'T', 'A', 'T', 'U', 'S', #0, 'E', 'V', 'A', 'R', 'R', 'E', 'C', 'I', 'D', #0, 'D', 'U', 'C', 'T', 'I', 'D', #0, #0, #0, #0, #0, #0, #0, #0)
//cbufl = 29
Move(cbufp^, cbuf, cbufl);
//Values immediately After Move should then be:
//cbuf = ('S', 'T', 'D', 'P', 'R', 'O', 'D', 'U', 'C', 'T', 'S', 'T', 'O', 'R', 'E', 'D', 'E', 'L', 'E', 'M', 'E', 'N', 'T', 'S', 'C', 'O', 'U', 'N', 'T', #0, #0)
//But sometimes this Move results in this value( 1 in 5..15 times):
//cbuf = ('S', 'T', 'D', 'P', 'R', 'O', 'D', 'U', 'C', 'T', 'S', 'T', 'O', 'R', 'E', 'D', #0, #0, #0, #0, #0, 'N', 'T', 'S', 'C', 'O', 'U', 'N', 'T', #0, #0) }
until SomeCondition;
//...Some more code
end;
