Debugging a DLL
lazarus / 12-Debugger

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Phil H. · 2005-11-10 20:04

How do you debug a DLL with Free Pascal/Lazarus?

The -gl switch doesn't display line tracing info if your program uses
SysUtils (what program doesn't?!). Setting ExceptProc := nil disables
SysUtils' exception handler, so line tracing is displayed. However,
this line tracing info doesn't work if they exception occurs in a DLL.
Instead, the trace shows only up to the call of the DLL function in
the main program, which is completely useless.

Trapping the exception in the DLL and executing

  WriteLn(BackTraceStrFunc(ExceptAddr));

displays the name of the source file and line number where the
exception occurred (for example, in one of the run-time units), but
not the place in the DLL source where the error started. How to trace
back to this error location? Normally this is what -gl does
automatically in an .exe.

Also, BackTraceStrFunc (and -gl) don't work right if the FPC-compiled
DLL is called by a non-FPC program.

Thanks.