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 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.
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
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.
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.
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 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.
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.
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:
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.
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 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. To create new filehandles other ops such as open would need to be enabled.
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.
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!
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.
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
reset
dbstate -- perl -d version of nextstate(ment) opcode
