[fpc-pascal] Corba ABI change ?

[Tony Whyman]

Supplementing my point below, I went back and checked my notes. The 
TObject layout post 3.2 (in my copy of trunk) is now

        TObject = class
        {$IFDEF SYSTEM_HAS_FEATURE_MONITOR}
        strict private
           _MonitorData : Pointer;
        private
           function SetMonitorData(aData,aCheckOld : Pointer) : Pointer; 
inline;
           function GetMonitorData: Pointer; inline;
        {$ENDIF}
        protected
           function GetDisposed : Boolean; inline;
           Property Disposed : Boolean Read GetDisposed;
        public

with everything before "public" having been added. The big change is the 
addition of "_MonitorData". This bumps the offset of all later fields up 
by sizeof(pointer). If you have code that makes assumptions about the 
object layout - and this very much applies to code that tries to import 
an object from C++ then your previous assumptions are invalid.

The advice I got was that for external interfaces, only the "record" 
layout is immutable between versions. In the end, I had to remove all 
the Firebird interface code that relied on the assumption that the 
Pascal object layout was the same as the C++ and replaced it with 
extended records in order to mimimise the impact on code that used the API.

There's more information about the changes to my code on github 
https://github.com/MWASoftware/fbintf/tree/main/client/3.0/firebird

On 18/02/2026 08:39, Tony Whyman via fpc-pascal wrote:
>
>     The object layout has changed post 3.2 with the addition of an
>     extra field. This breaks any code that makes assumptions about
>     this. I had a problem with the Firebird OO API due to this change
>     (also interfacing to C++), and had to rewrite the Firebird/IBX
>     interface moving away from OO to extended records.
>
>
> -------- Original message --------
> From: Adriaan van Os via fpc-pascal <fpc-pascal at lists.freepascal.org>
> Date: 17/02/2026 17:05 (GMT+00:00)
> To: FPC-Pascal users discussions <fpc-pascal at lists.freepascal.org>
> Cc: Adriaan van Os <adriaan at adriaan.biz>
> Subject: [fpc-pascal] Corba ABI change ?
>
> Has there been an ABI change in the trunk compiler (compared to 
> fpc-3.2.4-rc1) for CORBA interfaces
> ? Maybe related to "Unicode"-strings ? I have some C++ interfacing 
> code that works fine with
> fpc-3.2.4-rc1 but crashes with the trunk compiler.
>
> Any hints are appreciated.
>
> Regards,
>
> Adriaan van Os
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