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I have stumbled into what appears to me to be a compiler error, but before I post in the fpc list, I'd like to get expert advice. I have an application already in use since many years, which uses a thread to handle a serial line. I don't know if that second thread is related to the problem or not, but that is what I have. Now, in the main thread, which sends messages and receives answers, I wanted to measure the time from send to receive, therefore I added a TdateTime variable to do the job. The related snippets of code are as follows: TForm1 = class(TForm)
....
procedure SendMessage(Tipo,Lung: Byte);
....
public
{ Public declarations }
LastMsgTime: TDateTime;
end;
....
var
Form1: TForm1;
..
procedure TForm1.SendMessage(Tipo,Lung: Byte);
begin
...
LastMsgTime:= Now;
...
end;Now, whatever I do, with this code, I always get an access violation error for the LastMsgTime variable after a couple of messages have been sent and received. Suspecting that I could have some problems from the serial thread, I tried to change the way the main thread communicates with the main thread. I used a synchronize method to pass information from the serial thread to the main thread; I changed it with a message passing technique, i.e the serial thread uses a PostMessage to Form1.Handle but nothing changed. But I managed to make everything working perfectly if either: 1) I move the variable declaration out from the TForm1 Object type declaration: var Form1: TForm1; .... LastMsgTime: TDateTime;2) I change the code in SendMessage like that: procedure TForm1.SendMessage(Tipo,Lung: Byte); begin ... Form1.LastMsgTime:= Now; ... end;Which appears to me to be rather crazy, because to make it work I need to qualify an identifier which doesn't need to be qualified. The assembler generated in for the two cases is different (which IMHO shouldn't be): ULprog.pas:641 LastMsgTime:= Now; 00000000004FB500 e8bbc8feff callq 0x4e7dc0 <NOW> 00000000004FB505 488b45e8 mov -0x18(%rbp),%rax 00000000004FB509 f20f1180d0080000 movsd %xmm0,0x8d0(%rax) ULprog.pas:641 Form1.LastMsgTime:= Now; 00000000004FB500 e8bbc8feff callq 0x4e7dc0 <NOW> 00000000004FB505 488b050cce5000 mov 0x50ce0c(%rip),%rax # 0xa08318 00000000004FB50C 488b00 mov (%rax),%rax 00000000004FB50F f20f1180d0080000 movsd %xmm0,0x8d0(%rax)If in the first case I put a breakpont before the offending line, and I move the cursor to the variable name, the debugger tells that it cannot access memory at 0x8d0, in the second case everything works fine and the debugger just shows me the last value of LastMsgTime. I'm doing something wrong, I'm missing something, or this is just a compiler bug? Tested on a Linux platform, both with Lazarus 1.6 - fpc 3.0.0 and Lazarus 1.8 RC5 - fpc 3.1.1 Giuliano
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