Tcl Source Code

Copied email exchanges with Jeff.

Hi Eric,
 
Yes, I was able to repro it with a mem_debug build.  I 
also found that it is related to TCL_LINK_READ_ONLY - 
if you remove that, the error does not occur.  You should 
file this at http://tcl.sourceforge.net/ where it can be 
tracked through to fix.
 
Regards,
  Jeff Hobbs, The Tcl Guy
  http://www.ActiveState.com/, a division of Sophos 

-----Original Message-----
From: Tse, Eric [mailto:[email protected]] 
Sent: April 26, 2005 3:23 PM
To: [email protected]
Subject: RE: Tcl_LinkVar reproduced


Hi Jeff,

 

Can you reproduce it? Thanks,

 

ERic

 


--------------------------------------------------------------------------------

From: Tse, Eric 
Sent: Tuesday, April 26, 2005 11:31 AM
To: '[email protected]'
Subject: Tcl_LinkVar reproduced

 

Hi Jeff,

 

Here is the diff from 8.4.9:

 

*** tclTest.c   Tue Apr 26 11:11:02 2005

--- tclTest.c~  Mon Aug 30 12:58:48 2004

***************

*** 2482,2490 ****

   *----------------------------------------------------------------------

   */

  

- static int eric1 = 0;

- static int eric2 = 0;

- 

        /* ARGSUSED */

  static int

  TestlinkCmd(dummy, interp, argc, argv)

--- 2482,2487 ----

***************

*** 2502,2510 ****

      char buffer[2*TCL_DOUBLE_SPACE];

      int writable, flag;

      Tcl_Obj *tmp;

- 

-     Tcl_LinkVar(interp, "eric_var", (char *) &eric1, 
TCL_LINK_INT | TCL_LINK_READ_ONLY);

-     Tcl_LinkVar(interp, "eric_var", (char *) &eric2, 
TCL_LINK_INT | TCL_LINK_READ_ONLY);

  

      if (argc < 2) {

        Tcl_AppendResult(interp, "wrong # args: should be 
\"", argv[0],

--- 2499,2504 ----

 

 

 

Steps to reproduce:

-          gmake tcltest

-          tcltest

-          type “testlink” on the prompt

 

 

etse.cad889 [~/tmp/tcl8.4.9/unix]% tcltest

% testlink

file = ../generic/tclLink.c, line = 119

Trying to decrement refCount of previously disposed 
object.

Abort

 

Thanks,

Eric

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The problem is that Tcl_LinkVar tries to set the variable to
an obj with refCount 0. If that fails due to a trace (in the
example, because the variable was read only), the obj's
refcount is decremented by the SetVar code before returning,
and the obj is freed. Therefore, the code in Tcl_LinkVar
should not decrRefCount again.

This is a special of [Bug 1334947], which supersedes it.

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user_id=148712

This flew under my radar - upping prio to check for presence
in 8.4 and HEAD.