MirBSD manpage: Opcode(3p)

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

     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 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 exe-


     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 pur-

     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

     Each operator has both a terse name (its opname) and a more
     verbose or recognisable descriptive name. The opdesc func-
     tion 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

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     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

     a negated opname or optag
             An opname or optag can be prefixed with an exclama-
             tion mark, e.g., !mkdir. Negating an opname or optag
             means remove the corresponding ops from the accumu-
             lated 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

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 (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

     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

     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

             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

     opdesc (OP, ...)

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             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) pat-
             tern 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

     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 typi-
     cally 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

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              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 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 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 prob-
          able 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).

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

          These ops enable filehandle (rather than filename)
          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

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              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
          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 development
          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, optag!

              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


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          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) informa-
          tion about your system but not be able to change it.

              :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

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              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

              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 completeness 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,
     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.

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