Intercepting exceptions in a dll
lazarus / 67-Windows

----------------------------------------------------------------------
DenReq · 2022-05-11 13:10

Hello,

I hesitated to put this post in the "beginners" section.

I am trying to set up a Win32 DLL to intercept all the various
exceptions and errors that can occur, including in threads.

Currently I'm failing completely, and I think my inexperience with FPC
is most likely the cause. Something that seems pretty basic to me like
setting up an ErrorProc procedure, which is supposed to convert a call
to RunError into an exception, doesn't work at all: the set up
function is obviously not called and the program execution abruptly
terminates. This seems to me to be a sign that I'm missing something
as big as a house.

The minimal code is here. To me the call to TestExceptionRunError from
the host application should produce an exception intercepted by the
try except block, not terminate immediately. Am I making a mistake?

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i Library
FPCDLL; uses SysUtils; procedure TestExceptionRunError; stdcall;
export;    begin   try      RunError(123);   except   end; 
 end; Procedure RunErrorToExcept (ErrNo : Longint; Address :
CodePointer; Frame : Pointer);    begin   raise Exception.Create('Run
error '+IntToStr(ErrNo));   end; exports 
 TestExceptionRunError; beginErrorProc:=@RunErrorToExcept;end. 
I call FPC compiler using the following FPC.cfg file for options.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  -Twin32 -
ve -S2 -Sc -Se -Sg -Sm -Sd -FeErrPrg.Log -Ci- -
FuC:\FPC\3.2.2\units\i386-win32\fcl-base -gl -Rintel -MDelphi 
Could someone possibly give me an example of this kind of thing? I've
seen that exception handling in a DLL is a boring topic, but I must
not be the first one to break my teeth on this ?

Thanks in advance.

----------------------------------------------------------------------
PascalDragon · 2022-05-12 08:13

Some points:

you don't need to set ErrorProc, because the default handler provided
by the SysUtils unit already converts all run errorsyou don't need to
declare your TestExceptionRunError as export as you have it in the
exports clauseyour assumptions about the RunError function are wrong:
it does not use the exception handling hooks, but always terminates;
normal run errors (e.g. triggered by I/O errors) go through the
HandleError*-family of functions (and not RunErrror) which are handled
by the exception handling hooks and are not exported from the System
unit (so to test this you need to trigger a run error some other way)

----------------------------------------------------------------------
DenReq · 2022-05-16 07:18

Hello PascalDragon,

Thank you for the reply and the informations.

Regards