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Opcode(3p)       Perl Programmers Reference Guide      Opcode(3p)

       Opcode - Disable named opcodes when compiling perl code

         use Opcode;

       Perl code is always compiled into an internal format
       before execution.

       Evaluating perl code (e.g. via "eval" or "do 'file'")
       causes the code to be compiled into an internal format and
       then, provided there was no error in the compilation, exe-
       cuted.  The internal format is based on many distinct

       By default no opmask is in effect and any code can be com-

       The Opcode module allow you to define an operator mask to
       be in effect when perl next compiles any code.  Attempting
       to compile code which contains a masked opcode will cause
       the compilation to fail with an error. The code will not
       be executed.

       The Opcode module is not usually used directly. See the
       ops pragma and Safe modules for more typical uses.

       The authors make no warranty, implied or otherwise, about
       the suitability of this software for safety or security

       The authors shall not in any case be liable for special,
       incidental, consequential, indirect or other similar dam-
       ages arising from the use of this software.

       Your mileage will vary. If in any doubt do not use it.

Operator Names and Operator Lists
       The canonical list of operator names is the contents of
       the array PL_op_name defined and initialised in file
       opcode.h of the Perl source distribution (and installed
       into the perl library).

       Each operator has both a terse name (its opname) and a
       more verbose or recognisable descriptive name. The opdesc
       function can be used to return a list of descriptions for
       a list of operators.

       Many of the functions and methods listed below take a list
       of operators as parameters. Most operator lists can be
       made up of several types of element. Each element can be

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Opcode(3p)       Perl Programmers Reference Guide      Opcode(3p)

       one of

       an operator name (opname)
               Operator names are typically small lowercase words
               like enterloop, leaveloop, last, next, redo etc.
               Sometimes they are rather cryptic like gv2cv,
               i_ncmp and ftsvtx.

       an operator tag name (optag)
               Operator tags can be used to refer to groups (or
               sets) of operators.  Tag names always begin with a
               colon. The Opcode module defines several optags
               and the user can define others using the
               define_optag function.

       a negated opname or optag
               An opname or optag can be prefixed with an excla-
               mation mark, e.g., !mkdir.  Negating an opname or
               optag means remove the corresponding ops from the
               accumulated set of ops at that point.

       an operator set (opset)
               An opset as a binary string of approximately 44
               bytes which holds a set or zero or more operators.

               The opset and opset_to_ops functions can be used
               to convert from a list of operators to an opset
               and vice versa.

               Wherever a list of operators can be given you can
               use one or more opsets.  See also Manipulating
               Opsets below.

Opcode Functions
       The Opcode package contains functions for manipulating
       operator names tags and sets. All are available for export
       by the package.

       opcodes In a scalar context opcodes returns the number of
               opcodes in this version of perl (around 350 for

               In a list context it returns a list of all the
               operator names.  (Not yet implemented, use @names
               = opset_to_ops(full_opset).)

       opset (OP, ...)
               Returns an opset containing the listed operators.

       opset_to_ops (OPSET)
               Returns a list of operator names corresponding to
               those operators in the set.

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       opset_to_hex (OPSET)
               Returns a string representation of an opset. Can
               be handy for debugging.

               Returns an opset which includes all operators.

               Returns an opset which contains no operators.

       invert_opset (OPSET)
               Returns an opset which is the inverse set of the
               one supplied.

       verify_opset (OPSET, ...)
               Returns true if the supplied opset looks like a
               valid opset (is the right length etc) otherwise it
               returns false. If an optional second parameter is
               true then verify_opset will croak on an invalid
               opset instead of returning false.

               Most of the other Opcode functions call ver-
               ify_opset automatically and will croak if given an
               invalid opset.

       define_optag (OPTAG, OPSET)
               Define OPTAG as a symbolic name for OPSET. Optag
               names always start with a colon ":".

               The optag name used must not be defined already
               (define_optag will croak if it is already
               defined). Optag names are global to the perl pro-
               cess and optag definitions cannot be altered or
               deleted once defined.

               It is strongly recommended that applications using
               Opcode should use a leading capital letter on
               their tag names since lowercase names are reserved
               for use by the Opcode module. If using Opcode
               within a module you should prefix your tags names
               with the name of your module to ensure uniqueness
               and thus avoid clashes with other modules.

       opmask_add (OPSET)
               Adds the supplied opset to the current opmask.
               Note that there is currently no mechanism for
               unmasking ops once they have been masked.  This is

       opmask  Returns an opset corresponding to the current

       opdesc (OP, ...)
               This takes a list of operator names and returns

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               the corresponding list of operator descriptions.

       opdump (PAT)
               Dumps to STDOUT a two column list of op names and
               op descriptions.  If an optional pattern is given
               then only lines which match the (case insensitive)
               pattern will be output.

               It's designed to be used as a handy command line

                       perl -MOpcode=opdump -e opdump
                       perl -MOpcode=opdump -e 'opdump Eval'

Manipulating Opsets
       Opsets may be manipulated using the perl bit vector opera-
       tors & (and), | (or), ^ (xor) and ~ (negate/invert).

       However you should never rely on the numerical position of
       any opcode within the opset. In other words both sides of
       a bit vector operator should be opsets returned from
       Opcode functions.

       Also, since the number of opcodes in your current version
       of perl might not be an exact multiple of eight, there may
       be unused bits in the last byte of an upset. This should
       not cause any problems (Opcode functions ignore those
       extra bits) but it does mean that using the ~ operator
       will typically not produce the same 'physical' opset
       'string' as the invert_opset function.

TO DO (maybe)
           $bool = opset_eq($opset1, $opset2)  true if opsets are logically eqiv

           $yes = opset_can($opset, @ops)      true if $opset has all @ops set

           @diff = opset_diff($opset1, $opset2) => ('foo', '!bar', ...)

Predefined Opcode Tags
                null stub scalar pushmark wantarray const defined undef

                rv2sv sassign

                rv2av aassign aelem aelemfast aslice av2arylen

                rv2hv helem hslice each values keys exists delete

                preinc i_preinc predec i_predec postinc i_postinc postdec i_postdec
                int hex oct abs pow multiply i_multiply divide i_divide
                modulo i_modulo add i_add subtract i_subtract

                left_shift right_shift bit_and bit_xor bit_or negate i_negate
                not complement

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                lt i_lt gt i_gt le i_le ge i_ge eq i_eq ne i_ne ncmp i_ncmp
                slt sgt sle sge seq sne scmp

                substr vec stringify study pos length index rindex ord chr

                ucfirst lcfirst uc lc quotemeta trans chop schop chomp schomp

                match split qr

                list lslice splice push pop shift unshift reverse

                cond_expr flip flop andassign orassign and or xor

                warn die lineseq nextstate scope enter leave setstate

                rv2cv anoncode prototype

                entersub leavesub leavesublv return method method_named -- XXX loops via recursion?

                leaveeval -- needed for Safe to operate, is safe without entereval

            These memory related ops are not included in
            :base_core because they can easily be used to imple-
            ment a resource attack (e.g., consume all available

                concat repeat join range

                anonlist anonhash

            Note that despite the existance of this optag a mem-
            ory resource attack may still be possible using only
            :base_core ops.

            Disabling these ops is a very heavy handed way to
            attempt to prevent a memory resource attack. It's
            probable that a specific memory limit mechanism will
            be added to perl in the near future.

            These loop ops are not included in :base_core because
            they can easily be used to implement a resource
            attack (e.g., consume all available CPU time).

                grepstart grepwhile
                mapstart mapwhile
                enteriter iter
                enterloop leaveloop unstack
                last next redo

            These ops enable filehandle (rather than filename)

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            based input and output. These are safe on the assump-
            tion that only pre-existing filehandles are available
            for use.  To create new filehandles other ops such as
            open would need to be enabled.

                readline rcatline getc read

                formline enterwrite leavewrite

                print sysread syswrite send recv

                eof tell seek sysseek

                readdir telldir seekdir rewinddir

            These are a hotchpotch of opcodes still waiting to be

                gvsv gv gelem

                padsv padav padhv padany

                rv2gv refgen srefgen ref

                bless -- could be used to change ownership of objects (reblessing)

                pushre regcmaybe regcreset regcomp subst substcont

                sprintf prtf -- can core dump


                tie untie

                dbmopen dbmclose
                sselect select
                pipe_op sockpair

                getppid getpgrp setpgrp getpriority setpriority localtime gmtime

                entertry leavetry -- can be used to 'hide' fatal errors

                custom -- where should this go

            These ops are not included in :base_core because of
            the risk of them being used to generate floating
            point exceptions (which would have to be caught using
            a $SIG{FPE} handler).

                atan2 sin cos exp log sqrt

            These ops are not included in :base_core because they

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            have an effect beyond the scope of the compartment.

                rand srand

            These ops are related to multi-threading.

                lock threadsv

            A handy tag name for a reasonable default set of ops.
            (The current ops allowed are unstable while develop-
            ment continues. It will change.)

                :base_core :base_mem :base_loop :base_io :base_orig :base_thread

            If safety matters to you (and why else would you be
            using the Opcode module?)  then you should not rely
            on the definition of this, or indeed any other,

                stat lstat readlink

                ftatime ftblk ftchr ftctime ftdir fteexec fteowned fteread
                ftewrite ftfile ftis ftlink ftmtime ftpipe ftrexec ftrowned
                ftrread ftsgid ftsize ftsock ftsuid fttty ftzero ftrwrite ftsvtx

                fttext ftbinary


                ghbyname ghbyaddr ghostent shostent ehostent      -- hosts
                gnbyname gnbyaddr gnetent snetent enetent         -- networks
                gpbyname gpbynumber gprotoent sprotoent eprotoent -- protocols
                gsbyname gsbyport gservent sservent eservent      -- services

                gpwnam gpwuid gpwent spwent epwent getlogin       -- users
                ggrnam ggrgid ggrent sgrent egrent                -- groups

            A handy tag name for a reasonable default set of ops
            beyond the :default optag.  Like :default (and indeed
            all the other optags) its current definition is
            unstable while development continues. It will change.

            The :browse tag represents the next step beyond
            :default. It it a superset of the :default ops and
            adds :filesys_read the :sys_db.  The intent being
            that scripts can access more (possibly sensitive)
            information about your system but not be able to
            change it.

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                :default :filesys_read :sys_db

                sysopen open close
                umask binmode

                open_dir closedir -- other dir ops are in :base_io

                link unlink rename symlink truncate

                mkdir rmdir

                utime chmod chown

                fcntl -- not strictly filesys related, but possibly as dangerous?

                backtick system


                wait waitpid

                glob -- access to Cshell via <`rm *`>

                exec exit kill

                time tms -- could be used for timing attacks (paranoid?)

            This tag holds groups of assorted specialist opcodes
            that don't warrant having optags defined for them.

            SystemV Interprocess Communications:

                msgctl msgget msgrcv msgsnd

                semctl semget semop

                shmctl shmget shmread shmwrite

                flock ioctl

                socket getpeername ssockopt
                bind connect listen accept shutdown gsockopt getsockname

                sleep alarm -- changes global timer state and signal handling
                sort -- assorted problems including core dumps
                tied -- can be used to access object implementing a tie
                pack unpack -- can be used to create/use memory pointers

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                entereval -- can be used to hide code from initial compile
                require dofile

                caller -- get info about calling environment and args


                dbstate -- perl -d version of nextstate(ment) opcode

            This tag is simply a bucket for opcodes that are
            unlikely to be used via a tag name but need to be
            tagged for completness and documentation.

                syscall dump chroot

       ops(3) -- perl pragma interface to Opcode module.

       Safe(3) -- Opcode and namespace limited execution compart-

       Originally designed and implemented by Malcolm Beattie,
       mbeattieATsable.uk as part of Safe version 1.

       Split out from Safe module version 1, named opcode tags
       and other changes added by Tim Bunce.

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