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



NAME
       Opcode - Disable named opcodes when compiling perl code

SYNOPSIS
         use Opcode;

DESCRIPTION
       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, executed.  The internal format is
       based on many distinct opcodes.

       By default no opmask is in effect and any code can be compiled.

       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.

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

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

       The authors shall not in any case be liable for special, incidental, consequential, indirect or other
       similar damages 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 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 exclamation 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 perl-5.7.0).

               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.

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

       full_opset
               Returns an opset which includes all operators.

       empty_opset
               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 verify_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 process 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 intentional.

       opmask  Returns an opset corresponding to the current opmask.

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

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

Manipulating Opsets
       Opsets may be manipulated using the perl bit vector operators & (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
       :base_core
                null stub scalar pushmark wantarray const defined undef

                rv2sv sassign

                rv2av aassign aelem aelemfast aelemfast_lex aslice av2arylen

                rv2hv helem hslice each values keys exists delete aeach akeys avalues
                boolkeys reach rvalues rkeys

                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

                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 fc quotemeta trans transr chop schop chomp schomp

                match split qr

                list lslice splice push pop shift unshift reverse

                cond_expr flip flop andassign orassign dorassign and or dor xor

                warn die lineseq nextstate scope enter leave

                rv2cv anoncode prototype coreargs

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

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

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

                concat repeat join range

                anonlist anonhash

            Note that despite the existence of this optag a memory 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.

       :base_loop
            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
                goto

       :base_io
            These ops enable filehandle (rather than filename) based input and output. These are safe on the
            assumption that only pre-existing filehandles are available for use.  Usually, to create new
            filehandles other ops such as open would need to be enabled, if you don't take into account the
            magical open of ARGV.

                readline rcatline getc read

                formline enterwrite leavewrite

                print say sysread syswrite send recv

                eof tell seek sysseek

                readdir telldir seekdir rewinddir

       :base_orig
            These are a hotchpotch of opcodes still waiting to be considered

                gvsv gv gelem

                padsv padav padhv padany

                once

                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

                crypt

                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

                entergiven leavegiven
                enterwhen leavewhen
                break continue
                smartmatch

                custom -- where should this go

       :base_math
            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 have an effect beyond the scope of the
            compartment.

                rand srand

       :base_thread
            These ops are related to multi-threading.

                lock

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

                :base_core :base_mem :base_loop :base_orig :base_thread

            This list used to contain :base_io prior to Opcode 1.07.

            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, optag!

       :filesys_read
                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

                fileno

       :sys_db
                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

       :browse
            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.

                :default :filesys_read :sys_db

       :filesys_open
                sysopen open close
                umask binmode

                open_dir closedir -- other dir ops are in :base_io

       :filesys_write
                link unlink rename symlink truncate

                mkdir rmdir

                utime chmod chown

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

       :subprocess
                backtick system

                fork

                wait waitpid

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

       :ownprocess
                exec exit kill

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

       :others
            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

       :load
            This tag holds opcodes related to loading modules and getting information about calling
            environment and args.

                require dofile
                caller runcv

       :still_to_be_decided
                chdir
                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

                hintseval -- constant op holding eval hints

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

                reset

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

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

                syscall dump chroot

SEE ALSO
       ops -- perl pragma interface to Opcode module.

       Safe -- Opcode and namespace limited execution compartments

AUTHORS
       Originally designed and implemented by Malcolm Beattie, mbeattie@sable.ox.ac.uk as part of Safe
       version 1.

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



perl v5.16.2                                     2012-10-25                                      Opcode(3pm)