[Tcl-soc2008] Problem with Tcl_EvalObjv

[Remigiusz J. A. M. <lr...@go...>]

Hi,

Not the first, probably not the last - problem with Tcl_EvalObjv. Now 
I've got this here:
http://dev.lrem.net/tcldtrace/browser/trunk/generic/dtrace.c#L680
When executing this test:
http://dev.lrem.net/tcldtrace/browser/trunk/tests/dtrace.test#L484
I get a segfault. This is during the second call of callback. Everything 
looks quite the same as in the first call. Some gdb dump:
#v+

(gdb) p *objv[0]
$11 = {refCount = 1, bytes = 0x81aa938 "callback", length = 8,
   typePtr = 0xfef9e5b8, internalRep = {longValue = 139022144,
     doubleValue = 6.8686065361594778e-316, otherValuePtr = 0x8494f40,
     wideValue = 139022144, twoPtrValue = {ptr1 = 0x8494f40,
       ptr2 = 0x0}}}
(gdb) p *objv[1]
$12 = {refCount = 3, bytes = 0x0, length = 0, typePtr = 0xfef9e498,
   internalRep = {longValue = 135929976,
     doubleValue = 6.7158331381625143e-316, otherValuePtr = 0x81a2078,
     wideValue = 135929976, twoPtrValue = {ptr1 = 0x81a2078,
       ptr2 = 0x0}}}
(gdb) p *objv[2]
$13 = {refCount = 1, bytes = 0xfef9e674 "", length = 0,
   typePtr = 0x0, internalRep = {longValue = 138565592,
     doubleValue = 6.8460498702854665e-316, otherValuePtr = 0x84257d8,
     wideValue = 138565592, twoPtrValue = {ptr1 = 0x84257d8,
       ptr2 = 0x0}}}
(gdb) c
Continuing.

Program received signal SIGSEGV, Segmentation fault.
0xfef4ff59 in Tcl_NewStringObj () from /opt/tcldebug//lib/libtcl8.5.so
(gdb) bt
#0  0xfef4ff59 in Tcl_NewStringObj ()
    from /opt/tcldebug//lib/libtcl8.5.so
#1  0xfef52f82 in AppendPrintfToObjVA ()
    from /opt/tcldebug//lib/libtcl8.5.so
#2  0xfef531ca in Tcl_ObjPrintf ()
    from /opt/tcldebug//lib/libtcl8.5.so
#3  0xfef3adb0 in Tcl_LogCommandInfo ()
    from /opt/tcldebug//lib/libtcl8.5.so
#4  0xfeec1983 in Tcl_EvalObjv () from /opt/tcldebug//lib/libtcl8.5.so
#5  0xfeb92e36 in listProbe (handle=0x84554a8, pdesc=0x8045d3c,
     varg=0x8045f5c) at dtrace.c:706
[and a lot more]
#v+

Now, why would the refCount equal to 3? It's created just two lines 
before. It's the only visible difference between this and the previous 
instance of the function. I have no idea what to try now... Any help?

The test should fire the callback two times for probes 
syscall::exec:entry and syscall::exec:return.

BTW - how should I signalize an error within the callback? Like the 
failed Tcl_EvalObjv (if it would ever fail without bringing the whole 
thing down)?

Kind regards,
Remigiusz Modrzejewski