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

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
					       equivalent
	   $yes	= opset_can($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 kvaslice
		av2arylen

		rv2hv helem hslice kvhslice each values	keys exists delete
		aeach akeys avalues multideref argelem argdefelem argcheck

		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 nbit_and
		nbit_xor nbit_or sbit_and sbit_xor sbit_or negate i_negate not
		complement ncomplement scomplement

		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 avhvswitch anonconst

		entersub leavesub leavesublv return method method_named
		method_super method_redir method_redir_super
		 -- 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 padcv	padany padrange	introcv	clonecv

		once

		rv2gv refgen srefgen ref refassign lvref lvrefslice lvavref

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

		 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 v5.26.0			  2017-04-19			     Opcode(3)

NAME | SYNOPSIS | DESCRIPTION | NOTE | WARNING | Operator Names and Operator Lists | Opcode Functions | Manipulating Opsets | TO DO (maybe) | Predefined Opcode Tags | SEE ALSO | AUTHORS

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