[Tcl-bugs] [ tcl-Bugs-1923966 ] binary format crashes on x0s format string

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Bugs item #1923966, was opened at 2008-03-24 03:46
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Category: 16. Commands A-H
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Konstantin Khomoutov (flatworm)
Assigned to: Donal K. Fellows (dkf)
Summary: binary format crashes on x0s format string

Initial Comment:
[binary format] crashes when the "x" type character is present in the format string with the zero count attached and followed by any other meaningful type character that gets assigned a value:

% binary format x0s 1

Program received signal SIGSEGV, Segmentation fault.
0xb7edc7e0 in FormatNumber (interp=0x804c8d8, type=115, src=0x2, 
    cursorPtr=0xbfeceeb0)
    at /home/kostix/devel/src/tcl/unix/../generic/tclBinary.c:1756
1756            if (TclGetLongFromObj(interp, src, &value) != TCL_OK) {
(gdb) bt
#0  0xb7edc7e0 in FormatNumber (interp=0x804c8d8, type=115, src=0x2, 
    cursorPtr=0xbfeceeb0)
    at /home/kostix/devel/src/tcl/unix/../generic/tclBinary.c:1756
#1  0xb7edb42b in Tcl_BinaryObjCmd (dummy=0x0, interp=0x804c8d8, objc=4, 
    objv=0x804cf70)
    at /home/kostix/devel/src/tcl/unix/../generic/tclBinary.c:988
#2  0xb7ed6266 in TclEvalObjvInternal (interp=0x804c8d8, objc=4, 
    objv=0x804cf70, command=0xffffffff <Address 0xffffffff out of bounds>, 
    length=-1, flags=0)
    at /home/kostix/devel/src/tcl/unix/../generic/tclBasic.c:3649
#3  0xb7f2da77 in TclExecuteByteCode (interp=0x804c8d8, codePtr=0x806b8d0)
    at /home/kostix/devel/src/tcl/unix/../generic/tclExecute.c:2314
#4  0xb7f2b897 in TclCompEvalObj (interp=0x804c8d8, objPtr=0x805c228, 
    invoker=0x0, word=0)
    at /home/kostix/devel/src/tcl/unix/../generic/tclExecute.c:1460
#5  0xb7ed7c22 in TclEvalObjEx (interp=0x804c8d8, objPtr=0x805c228, 
    flags=131072, invoker=0x0, word=0)
    at /home/kostix/devel/src/tcl/unix/../generic/tclBasic.c:4763
#6  0xb7ed7730 in Tcl_EvalObjEx (interp=0x804c8d8, objPtr=0x2, flags=131072)
    at /home/kostix/devel/src/tcl/unix/../generic/tclBasic.c:4555
#7  0xb7f4418c in Tcl_RecordAndEvalObj (interp=0x804c8d8, cmdPtr=0x805c228, 
    flags=131072)
    at /home/kostix/devel/src/tcl/unix/../generic/tclHistory.c:161
#8  0xb7f67b4d in Tcl_Main (argc=-1, argv=0xbfecff68, 
    appInitProc=0x804864b <Tcl_AppInit>)
    at /home/kostix/devel/src/tcl/unix/../generic/tclMain.c:554
#9  0x0804863c in main (argc=Cannot access memory at address 0x73
)
    at /home/kostix/devel/src/tcl/unix/../unix/tclAppInit.c:87

Verified to crash current CVS HEAD (8.5.1b2) and 8.4.16.

Probably the "x" type character with zero count should be treated as no-op (since it is a no-op, logically). Halding of this is useful for auto-generated format strings, such as in
set pad [calculate NUL-padding]
append s [binary format x${pad}... ...]


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