[Lazarus] Windows exceptions and gdb

Martok listbox at martoks-place.de
Tue Mar 8 19:20:28 CET 2016


this isn't technically a Lazarus issue but a gdb one, but maybe someone here
(Sven?) has encountered this before and knows what to do. I think this is
related to the discussion we had on #24908, and my lack of understanding back

Take this example program, compile with -Pi386 and execute on a 64bit Windows
(Wow64, reproduced on 8.1 and 10). This might also apply to pure 32bit Windows,
but I currently don't have any available to test.

program Project1;
uses Windows;

This will execute fine when called directly:


But from gdb, Windows' internal use of exceptions confuses gdb and it doesn't
continue properly:

  (gdb) r
  Starting program: ...\Temp\project1.exe
  [New Thread 1444.0x1240]
  gdb: unknown target exception 0xc0000008 at 0x7737c56c

  Program received signal ?, Unknown signal.
  0x7737c56c in ntdll!ZwClose () from C:\Windows\SYSTEM32\ntdll.dll
  (gdb) c
  [Inferior 1 (process 1444) exited with code 030000000010]

This issue is not new, an explanation can be found in this 9 year old list
reply: <https://sourceware.org/ml/gdb/2007-10/msg00162.html> In a nutshell, gdb
passes an exception back to the application that was only intended as a hint for
the debugger. It goes unhandled there (obiously) and Windows then kills the
application. There was a patch that would have fixed the situation, but
apparently that never landed

Is there any way to "fix"/avoid this from our side? This currently completely
breaks debugging on Wow64 in some situations... note that the example above is
just a simple version, gdb chokes as soon as anyone in the current process
throws an EXCEPTION_INVALID_HANDLE: drivers, codecs, ActiveX-objects, ...

I'd be grateful for any help,



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