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

       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, 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.

       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 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

       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

	       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 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
	   $yes = opset_can($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 aelemfast_lex aslice av2arylen

		rv2hv helem hslice each values keys exists delete aeach akeys
		avalues 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

	    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.

	    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) 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

	    These are a hotchpotch of opcodes still waiting to be considered

		gvsv gv gelem

		padsv padav padhv padcv padany padrange introcv clonecv


		rv2gv refgen srefgen ref

		bless -- could be used to change ownership of objects

		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

		entergiven leavegiven
		enterwhen leavewhen
		break continue

		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.


	    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!

		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.

		: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

		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

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

		require dofile
		caller runcv

		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


		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

		syscall dump chroot

       ops -- perl pragma interface to Opcode module.

       Safe -- Opcode and namespace limited execution compartments

       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 v5.18.2			  2014-01-06			 Opcode(3perl)

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