[Tcl-bugs] [ tcl-Bugs-1876793 ] Odd crash with args/lreverse/lrange combination

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Bugs item #1876793, was opened at 2008-01-21 22:18
Message generated for change (Settings changed) made by tallniel
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Category: 14. List Object
Group: development: 8.5.1b1
Status: Open
Resolution: None
>Priority: 9
Private: No
Submitted By: Neil Madden (tallniel)
Assigned to: Jan Nijtmans (nijtmans)
Summary: Odd crash with args/lreverse/lrange combination

Initial Comment:
I am seeing a bus error on Mac OS X 10.4.11 (Intel) using current Tcl CVS HEAD. A minimal script to reproduce the crash is the following:

proc foo args {
    set n [lrange $args 0 end]
    lreverse [lrange $n 0 end-1]
}
foo bar

I'm not entirely sure where the problem lies, but it seems to be some combination of the use of "args", the 2 uses of "lrange", and it seems to rely on the "end-N" syntax (just "lrange $n 0 end" doesn't cause a bus error). I suspect a tricky ref-counting bug somewhere and am investigating further. I'll add more here if I track it down.

Neil

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Comment By: Neil Madden (tallniel)
Date: 2008-01-21 22:33

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Originator: YES

gdb isn't showing much interesting as is typical with ref-counting bugs:
the location of the error is well removed from where the memory violation
shows up. An even more minimal script is:

lreverse [lrange [lrange foo 0 end] 0 end-1]
or
lreverse [lrange [lrange foo 0 end-1] 0 end]

Both lreverse and the end-1 syntax seem to be needed, but "args" is a red
herring.

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