[Tcl-bugs] [ tcl-Bugs-3098302 ] Bytecode for [catch] causes crash

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Bugs item #3098302, was opened at 2010-10-29 16:29
Message generated for change (Comment added) made by dkf
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Category: 47. Bytecode Compiler
Group: development: 8.6b1.1
Status: Open
Resolution: None
Priority: 7
Private: No
Submitted By: Kevin B KENNY (kennykb)
Assigned to: Don Porter (dgp)
Summary: Bytecode for [catch] causes crash

Initial Comment:
If a [catch {some script} result] or [catch {some script} result options] has a write trace fail on the 'result' or 'options' variables, the 'endCatch' bytecode for the catch block gets bypassed, and the exception stack becomes unbalanced. The result is somewhat unpredictable, but likely to be unamusing:

Test case:

proc failtrace {n1 n2 op} {
    return -code error "trace on $n1 fails by request"
}
trace add variable result1 write failtrace

proc x {} {
    variable result1
    for {set i 0} {$i < 100} {incr i} {
	set status2 [catch {
	    set status1 [catch {
		return -code error -level 0 "original failure"
	    } result1 options1]
	} result2 options2]
	lappend retval $status2 $result2 $options2
    }
}

puts [x]

Test result:

Bad stack top 7 at pc 144 in TclNRExecuteByteCode (min 0, max 6)
 executing lappend retval $status2 $result2 $options2
TclNRExecuteByteCode execution failure: bad stack top

Will follow up on tcl-core.


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>Comment By: Donal K. Fellows (dkf)
Date: 2010-11-02 20:09

Message:
I *think* the patch is correct.

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You can respond by visiting: 
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