[Tcl-bugs] [ tcl-Bugs-730244 ] missing refCount management in Tcl_EvalObjv

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Bugs item #730244, was opened at 2003-04-30 11:34
Message generated for change (Comment added) made by dgp
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Category: 44. Parsing and Eval
Group: 8.4.2
Status: Open
Resolution: None
Priority: 5
Submitted By: Don Porter (dgp)
Assigned to: miguel sofer (msofer)
Summary: missing refCount management in Tcl_EvalObjv

Initial Comment:

This script panics:

interp create i
proc test args {puts $args}
trace add execution test enter {interp alias i alias {} ;#}
interp alias i alias {} test this
i eval alias

The problem is that TEOVI does not use
refCounting to protect the elements of
the objv array.  So if a trace frees an
argument value, that value is not available
for command procedure execution.

Most TEOVI callers manage refCounts,
but Tcl_EvalObjv does not; thus interp alias
calls do not.

A fix is to add objv refCounting to Tcl_EvalObjv,
at an unknown performance cost.

Thoughts?

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>Comment By: Don Porter (dgp)
Date: 2003-04-30 13:58

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my comment about Tcl_EvalEx's need
for refCounts was incorrect.  Since it
pulls values from the interp result, it
needs to claim each one before moving
on to do substitutions for the next one.

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Comment By: miguel sofer (msofer)
Date: 2003-04-30 12:49

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The TclInterpReady difference may actually be a bug in TEBC:
[Bug 495830]


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Comment By: Don Porter (dgp)
Date: 2003-04-30 12:26

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this issue combined with
TclInterpReady checks
and numLevels management
suggest that the TEOVI callers
in tclBasic.c really have different
needs from the caller in tclExecute.c.

Another level of wrapping could help here.

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Comment By: Don Porter (dgp)
Date: 2003-04-30 11:51

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there's any number of solutions, but it's best
not to get too tricky, and expecially best not
to let the trickiness escape to the public interface.

Would be best if each routine in the core managed
refCounts according to its own needs rather than
serving callers, or called routines.

TEOVI is what needs refCounts, to preserve objs
across trace and normal execution calls.

Tcl_EvalEx, for example, currently does incr/decr
of refcounts, even though it doesn't really need to.
It does only one thing with objv, pass it in to TEOVI.

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Comment By: miguel sofer (msofer)
Date: 2003-04-30 11:40

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Another fix is to document that TEOV requires that the
caller hold a counted reference to its arguments, and insure
that all core calls respect this. No performance cost for
bytecodes (which do not suffer this problem), more
complexity ...

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