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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 v5.16.3				    2013-03-04				      Opcode(3pm)
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