IBX fbintf isc_start_transaction exception on Win64
lazarus / 16-Databases

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ttomas · 2024-02-01 20:25

Using only fbintf and trying to connect to Fb3/4/5 with legacy
interface (-dLEGACYFIREBIRDAPIONLY) on Win64 TCP connection, some
times isc_start_transaction raise exception "Access violation reading
from addresss...".
Win32 Local and Remote and Win64 Local(Embedded) connection never
raise exception, only Win64 Remote localhost:mybase.fdb.
Can you check isc_start_transaction definition, its look like some
stack corruption. In program that work, changing some lines, start
raising this exception.
USEFIREBIRD3API don't have this problem.
In ibase.h isc_start_transaction is defined as
Code: [Select]ISC_STATUS ISC_EXPORT_VARARG
isc_start_transaction(ISC_STATUS*,
                                           isc_tr_handle*,
                                           short, ...);
I solve the problem with this change in client\IB_Header
Code: [Select]Tisc_start_transaction = function (status_vector       
  : PISC_STATUS;
                                tran_handle               :
PISC_TR_HANDLE;
                                db_handle_count           : Short):
ISC_STATUS;
                                cdecl; varargs;
In fpc 3.2fix packages\ibase\src\ibase60.inc this function is defined
as
Code: [Select]function isc_start_transaction(_para1:PISC_STATUS;
 _para2:Pisc_tr_handle;
 _para3:smallint;
 args:array of const):ISC_STATUS;
 cdecl; external gdslib;
fbintf 1.4, Win 10 x64, Lazarus 3, Fpc 3.2fix

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tonyw · 2024-02-01 22:55

Interesting...

This type definition is largely unchanged from the original Borland
IBX. The only change I have made was to change PChar to PByte (to keep
Delphi happy).

The InterBase 6 API guide defines the function as:

Code: C  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i ISC_STATUS
isc_start_transaction(ISC_STATUS *status_vector,isc_tr_handle
*trans_handle,short db_handle_count,isc_db_handle *db_handle,unsigned
short tpb_length,char *tpb_address,[isc_db_handle *db_handle,unsigned
short tpb_length,char *tpb_address ...]);
which in IBHeader.pas is translated to

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 function
(status_vector           : PISC_STATUS;                              
 tran_handle               : PISC_TR_HANDLE;                         
      db_handle_count           : Short;                             
  db_handle                 : PISC_DB_HANDLE;                        
       tpb_length                : UShort;                           
    tpb_address               : PByte): ISC_STATUS;                  
            cdecl;   
i.e. only a single database group is supported.

Given that start_transaction is only ever called by IBX to start a
transaction against a single database, this definition has sufficed
for the last 25 or so years (start_multiple is used by IBX to start a
transaction against multiple databases). My guess is that the IBX
definition predated Delphi support for varargs - and maybe
start_multiple was added to in InterBase API in consequence.

So the interesting question is why has this bug suddenly arisen? Is
there something different in the way 'C' handles varargs in win64
compared with win32 or Linux (32 and 64)?

Before publishing a change to use varargs, I will need to check out
the behaviour under all platforms and not just win64.

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ttomas · 2024-02-02 00:52

Yes must be checked on all platforms.
This simple test in attach don't raise exception. Debugging/Watching
in TFB25Transaction.InternalStartSingle, I change code to
Code: [Select]procedure
TFB25Transaction.InternalStartSingle(attachment: IAttachment);
var db_handle: TISC_DB_HANDLE;
    pb: PByte;  // add
    i: integer;  // add
begin
  with FFirebird25ClientAPI do
  try
    db_handle := (attachment as TFB25Attachment).Handle;
    pb := (FTPB as TTPB).getBuffer;  //add
    Call(isc_start_transaction(StatusVector, @FHandle,1,
              @db_handle,(FTPB as TTPB).getDataLength,(FTPB as
TTPB).getBuffer));
  except
    FHandle := nil;
    raise;
  end
end;
And exception start raising. If you remove dummy/not used var i,
exception is not raising.