=head1 TITLE

Parrot Assembly Language

=head1 VERSION

=head2 CURRENT

    Maintainer: Dan Sugalski
    Class: Internals
    PDD Number: 6
    Version: 1.6
    Status: Developing
    Last Modified: 05 November 2001
    PDD Format: 1
    Language:English

=head2 HISTORY

=over 4

=item Version 1.6

November 05, 2001

=item Version 1.5

October 12, 2001

=item Version 1.4

September 24, 2001

=item Version 1.3

September 12, 2001

=item Version 1.2

August 25, 2001

=item Version 1.1

August 8, 2001

=item version 1

None. First version

=back

=head1 CHANGES

=over 4

=item Version 1.6

=over 4

=item * Added GC opcodes

=back

=item Version 1.5

=over 4

=item * Now have a bsr in addition to a jsr

=item * return is now ret

=item * Added save and restore ops for saving and restoring individual registers

=back

=item Version 1.4

=over 4

=item * Conditional branches have just a true destination now

=item * Added the I/O ops

=item * Added in the threading ops

=item * Added in the interpreter ops

=back

=item Version 1.3

=over 4

=item * Added in the low-level module loading ops

=item * Added in transcendental functions and modulo

=item * Finished the pad/global variable fetching bits

=back

=item Version 1.2

We have an interpreter now! Yay! (Okay, a simple one, but still...)
Changes made to reflect that.

=item Version 1.1

=over 4

=item * Added in object 

=item * Changed remnants of "perl" to "Parrot"

=item * Branch destination may be integer constant

=item * Added L<Assembly Syntax> section

=back

=item Version 1.0

None. First version

=back

=head1 ABSTRACT

This PDD describes the format of Parrot's bytecode assembly language.

=head1 DESCRIPTION

Parrot's bytecode can be thought of as a form of machine language
for a virtual super CISC machine. It makes sense, then, to define an
assembly language for it for those people who may need to generate
bytecode directly, rather than indirectly via the perl (or any other)
language.

=head1 IMPLEMENTATION

Parrot opcodes take the format of:

  code destination[dest_key], source1[source1_key], source2[source2_key]

The brackets do not denote optional arguments as such--they are real
brackets. They may be left out entirely, however. If any argument has
a key the assembler will substitute the null key for arguments missing keys.

Conditional branches take the format:

  code boolean[bool_key], true_dest

The key parameters are optional, and may be either an integer or a
string. If either is passed they are associated with the parameter to
their left, and are assumed to be either an array/list entry number,
or a hash key. Any time a source or destination can be a PMC register,
there may be a key.

Destinations for conditional branches are an integer offset from the
current PC.

All registers have a type prefix of P, S, I, or N, for PMC, string,
integer, and number respectively.

=head1 Assembly Syntax

All assembly opcodes contain only ASCII lowercase letters and the underscore.

Upper case names are reserved for assembler directives.

Labels all end with a colon. They may have ASCII letters, numbers, and
underscores in them. Labels that begin with a dollar sign (the only
valid spot in a label a dollar sign can appear) are private to the
subroutine they appear in.

Namespaces are noted with the NAMESPACE directive. It takes a single
parameter, the name of the namespace. Multilevel namespaces are
supported, and the namespaces should be double-colon separated.

Subroutine names are noted with the SUB directive. It takes a single
parameter, the name of the subroutine, which is added to the
namespace's symbol table. Sub names may be any valid Unicode
alphanumeric character and the underscore.

String and integer constants don't need to be put in a separate 


=head1 OPCODE LIST

In the following list, there may be multiple (but unlisted) versions
of an opcode. If an opcode takes a register that might be keyed, the
keyed version of the opcode has a _k suffix. If an opcode might take
multiple types of registers for a single parameter, the opcode
function really has a _x suffix, where x is either P, S, I, or N,
depending on whether a PMC, string, integer, or numeric register is
involved. The suffix isn't necessary (though not an error) as the
assembler can intuit the information from the code.

In those cases where an opcode can take several types of registers,
and more than one of the sources or destinations are of variable type,
then the register is passed in extended format. An extended format
register number is of the form:

     register_number | register_type

where register_type is 0x100, 0x200, 0x400, or 0x800 for PMC, string,
integer, or number respectively. So N19 would be 0x413.

B<Note>: Instructions tagged with a * will call a vtable method to
handle the instruction if used on PMC registers.

In all cases, the letters x, y, and z refer to register numbers. The
letter t refers to a generic register (P, S, I, or N). A lowercase p,
s, i, or n means either a register or constant of the appropriate type
(PMC, string, integer, or number)

=head2 Control flow

The control flow opcodes check conditions and manage program flow.

=over 4

=item if tx, X

Check register tx. (Px, Sx, Ix, or Nx) If true, branch by X.

=item jump tx

Jump to the address held in register x (Px, Sx, or Ix).

=item branch tx

Branch forward or backward by the amount in register x. (X may be
either Ix, Nx, or Px) Branch offset may also be an integer constant.

=item jsr tx

Jump to the location specified by register X. Push the current
location onto the call stack for later returning.

=item bsr ix

Branch to the location specified by X (either register or label). Push
the current location onto the call stack for later returning.

=item ret

Pop the location off the top of the stack and go there.

=back

=head2 Data manipulation

These ops handle manipulating the data in registers

=over 4

=item new Px, Iy

Create a new PMC of class y stored in PMC register x.

=item destroy Px

Destroy the PMC in register X, leaving it undef

=item set tx, ty

Copies y into x. Note that strings and PMCs are referred to by
pointer, so if you do something like:

   set S0, S1

this will copy the pointer in S1 into S0, leaving B<both> registers
pointing at the same string.

=item assign Px, ty

Takes the contents of Y and assigns them into the existing PMC in X.

While set just copies pointers from one register to another, assign
actually does a value assignment, as:

    $foo = $bar;

X's assign vtable method is invoked and it does whatever is appropriate.

=item clone Px, Py

=item clone Sx, xy

Performs a "deeper" copy of y into x, using the vtable appropriate
to the class of Py if cloning a PMC.

=item tostring Sx, ty, Iz

Take the value in register y and convert it to a string of type z,
storing the result in string register x.

=item add tx, ty, tz *

Add registers y and z and store the result in register
x. (x = y + z) The registers must all be the same type, PMC, integer,
or number.

=item sub tx, ty, tz *

Subtract register z from register y and store the result in register
x. (x = y - z) The registers must all be the same type, PMC, integer,
or number.

=item mul tx, ty, tz *

Multiply register y by register z and store the results in register
x. The registers must be the same type.

=item div tx, ty, tz *

Divide register y by register z, and store the result in register x.

=item inc tx, nn *

Increment register x by nn. nn is an integer constant. If nn is
omitted, increment is 1.

=item dec tx, nn *

Decrement register x by nn. nn is an integer constant. If nn is
omitted, decrement by 1.

=item length Ix, Sy

Put the length of string y into integer register x.

=item concat Sx, Sy

Add string y to the end of string x.

=item repeat Sx, Sy, Iz

Copies string y z times into string x.

=back

=head2 Transcendental operations

These opcodes handle the transcendental math functions. The
destination register here must always be either a numeric or a PMC
register.

=over 4

=item sin nx, ty

Return the sine of the number in Y

=item cos nx, ty

Return the cosine of the number in Y

=item tan nx, ty

Return the tangent of the number in Y

=item sec nx, ty

Return the secant of the number in Y

=item atan nx, ty

Return the arctangent of Y

=item atan2 nx, ty

Return the result of atan2 of Y

=item asin nx, ty

Return the arcsine of y

=item acos nx, ty

Return the arccosine of y

=item asec nx, ty

Return the arcsecant of y

=item cosh nx, ty

Return the hyperbolic cosine of y

=item sinh nx, ty

Return the hyperbolic sine of y

=item tanh nx, ty

Return the hyperbolic tangent of y

=item sech nx, ty

Return the hyperbolic secant of y

=item log2 nx, ty

Return the base 2 log of y

=item log10 nx, ty

Return the base 10 log of y

=item ln Nx, ty

Return the base e log of y

=item log nx, ty, tz

Return the base Z log of Y

=item pow nx, ty, tz

Return Y to the Z power

=item exp nx, ty

Return e to the Y power

=back

=head2 Register and stack ops

These opcodes deal with registers and stacks

=over 4

=item push_p

Push the current frame of PMC registers onto their stack and start a
new frame. The new registers are not initialized.

=item push_p_c

Push the current frame of PMC registers onto their stack and start a
new frame. The new registers are copies of the previous frame.

=item pop_p

Pop the current frame of PMC registers off the stack.

=item push_i

The same as L<push_p>, for the integer register set.

=item push_i_c

The same as L<push_p_c>, for the integer register set.

=item pop_i

The same as L<pop_p>, for the integer register set.

=item push_s

The same as L<push_p>, for the string register set.

=item push_s_c

The same as L<push_p_c>, for the string register set.

=item pop_s

The same as L<pop_p>, for the string register set.

=item push_n

The same as L<push_p>, for the floating-point register set.

=item push_n_c

The same as L<push_p_c>, for the floating-point register set.

=item pop_n

The same as L<pop_p>, for the floating-point register set.

=item save_i Ix

Push register X onto the generic stack

=item save_s Sx

Push register X onto the generic stack

=item save_p Px

Push register X onto the generic stack

=item save_n Nx

Push register X onto the generic stack

=item restore_i Ix

Restore register X from the generic stack

=item restore_s Ix

Restore register X from the generic stack

=item restore_p Px

Restore register X from the generic stack

=item restore_n Nx

Restore register X from the generic stack

=item entrytype Ix, iy

Put the type of stack entry Y into integer register X

=item set_warp string

Sets a named marker for the stacks for later use.

=item lookback tx, Iy

Fetch the entry that's at position Y from the top of the stack. This
does not remove an entry from the stack, merely fetches the entry off
it.

0 is the entry from the top of the stack, 1 is the entry immediately
previous to that, and so on. Entry -1 is the very bottom-most entry in
the stack. (While the stack may be a tree when looked at from the bottom up, you
don't have access to any other branches when looking this way)

=item warp [string]

Reset the current register stacks to the state they were in when the
warp was set. Resets only the frame pointers, doesn't guarantee the
contents of the registers. Be I<very> careful modifying the frame
pointers by, for example, pushing register frames.

If a name is passed, warp back to the named point.

=item unwarp

Reset the current register stacks to the state they were in before the
last warp.

=back

=head2 Names, pads, and globals

These operations are responsible for finding names in lexical or
global scopes, as well as storing data into those slots and checking
constraints on those slots. They also allocate and deallocate
scratchpads and entries in those pads.

Pad descriptors are templates for a particular pad. They are specified
in the constant area of a bytecode file, and contain the names, types,
and attributes for the variables referenced in the scope the pad is for.

The pad 0 is special, and represents the empty pad.

=over 4

=item find_lex Px, sy

Find the lexical of name sy and store the PMC pointer in register Px.

=item find_global Px, sy, sz

Find the PMC for the global variable sy from the table sz and store it
in register X

=item find_global Px, sy

Find the PMC for the global in the default table and put it in X.

=item find_global_table Px, sy

Find the global symbol table Y and store its PMC in X

=item find_global_slot ix, Py, sz

Find the slot in the global table Y for the global named Z, and store
its slot in register X.

=item fetch_lex Px, iy, iz

Fetch the lexical in slot y of scratchpad z. If z is negative, search
out from the current pad, if positive search inwards from the
outermost pad. Put the resulting PMC pointer in register x

=item fetch_global Px, Py, iz

Fetch the global in slot Z of the symbol table pointed to by Y

=item store_global Px, sy

Store X in the default global symbol table with a name of Y.

=item newpad pad_descriptor

Create a new scratchpad using pad_descriptor as a template.

=back

=head2 Exceptions

These opcodes deal with exception handling at the lowest
level. Exception handlers are dynamically scoped, and any exception
handler set in a scope will be removed when that scope is exited.

=over 4

=item set_eh Px

Sets an exception handler in place. The code referred to by register
Px will get called if an exception is thrown while the exception
handler is in scope.

=item clear_eh

Clear out the most recently placed exception 

=item throw Px

Throw an exception represented by the object in PMC register x. 

=item rethrow Px

Only valid inside an exception handler. Rethrow the exception
represented by the object in PMC register x. This object may have been
altered by the exception handler.

=back

=head2 Object things

These opcodes deal with PMCs as objects, rather than as opaque data
items.

=over 4

=item make_object Px, ty

Make the variable in PMC x an object of type ty. The type can be a
string, in which case we treat it as a package name.

=item find_method Px, Py, tz

Find the method Z for object Y, and return a PMC for it in X.

=item call_method Px, ty

=item find_attribute Px, sy

=item set_attribute Px, ty, tz

=item can Px, ty

=item isa Px, ty

=back

=head2 Module handling

These opcodes deal with loading in bytecode or executable code
libraries, and fetching info about those libraries. This is all
dealing with precompiled bytecode or shared libraries.

=over 4

=item load_bytecode sx

Load in the bytecode in file X. Search the library path if need be.

=item load_opcode_lib sx, iy

Load in the opcode library X, starting at opcode number Y. Search the
path if needed.

=item load_string_lib sx

Load in the string handling library named X

=item get_op_count sx

Return the number of opcodes in opcode library X

=item get_string_name sx

Get the name of the string encoding that the library X handles

=item find_string_lib sx, sy

Find the string library that handles strings of type Y. Return its
name in X.

=back

=head2 I/O operations

Reads and writes read and write records, for some value of record. 

=over 4

=item new_fh px

Create a new filehandle px

=item open px, sy

Open the file Y on filehandle X

=item read px, py, pz

Issue a read on the filehandle in y, and put the result in PMC
X. PMC Z is the sync object.

=item write px, sy, pz

Write the string Y to filehandle X. PMC Z is the sync object.

=item wait px

Wait for the I/O operation represented by sync object X to finish

=item readw px, py

Read from filehandle Y and put the results in PMC X. Blocks until the
read completes.

=item writew px, sy

Write string Y to filehandle X, waiting for the write to complete.

=item seek px, ty

Seek filehndle X to position Y.

=item tell tx, py

Return the current position of filehandle Y and put it in X. Returns
-1 for filehandles where this can't be determined. (Such as stream
connections)

=item status px, py, tz

Get informational item Z for filehandle Y and put the result in
X. This fetches things like the number of entries in the IO pipe,
number of outstanding I/O ops, number of ops on the filehandle, and so
forth.

=back

=head2 Threading ops

=over 4

=item lock Px

Take out a high-level lock on the PMC in register X

=item unlock Px

Unlock the PMC in register X

=item pushunlock Px

Push an unlock request on the stack

=back

=head2 Interpreter ops

=over 4

=item newinterp Px, flags

Create a new interpreter in X, using the passed flags.

=item runinterp Px, iy

Jump into interpreter X and run the code starting at offset Y from the
current location. (This is temporary until we get something better)

=item callout Pw, Px, sy, pz

Call routine Y in interpreter x, passing it the list of parameters
Z. V is a synchronization object returned. It can be waited on like
the sync objects returned from async I/O routines.

=item interpinfo Ix, iy

Get information item Y and put it in register X. Currently defined are:

=over 4

=item 1 TOTAL_MEM_ALLOC

The total amount of system memory allocated for later parceling out
to Buffers. Doesn't include any housekeeping memory, memory for Buffer
or PMC structs, or things of that nature.

=item 2 DOD_RUNS

The total number of dead object detection runs that have been made.

=item 3 COLLECT_RUNS

The total number of memory collection runs that have been made.

=item 4 ACTIVE_PMCS

The number of PMCs considered active. This means the DOD scan hasn't
noted them as dead.

=item 5 ACTIVE_BUFFERS

The number of Buffers (usually STRINGs but could be other things)
considered active.

=item 6 TOTAL_PMCS

The total number of PMCs the interpreter has available. Includes both
active and free PMCs

=item 7 TOTAL_BUFFERS

The total number of Buffer structs the interpreter has available.

=item 8 HEADERS_ALLOC_SINCE_COLLECT

The number of new Buffer header block allocations that have been made since
the last DOD run. (Buffers, when allocated, are allocated in chunks)

=item 9 MEM_ALLOCS_SINCE_COLLECT

The number of times we've requested a block of memory from the system
for allocation to Buffers since the last time we compacted the memory heap.

=back

=back

=head2 Garbage collection

=over 4

=item sweep

Fire off a dead object sweep

=item collect

Fire off a garbage collection sweep

=item pausecollect

Pause the garbage collector. No collections will be done for this interpreter
until the collector is unpaused.

=item resumecollect

Unpause the collector. This doesn't necessarily do a GC run, merely
allows the interpreter to fire one off when it deems it necessary.

=back

=head2 Key operations

Keys are used to get access to individual elements of an aggregate
variable.  This is done to allow for opaque, packed, and
multidimensional aggregate types.

A key entry may be an integer, string, or PMC. Integers are used for
array lookups, strings for hash lookups, and PMCs for either. 

=over 4

=item new_key Sx

Create a new key structure and put a pointer to it in register X.

=item clone_key Sx, ky

Make a copy of the key Y and put a pointer to it in register X. Y may
be either an S register or a constant.

=item size_key Sx, iy

Make the key structure X large enough to hold Y key entries

=item key_size Ix, ky

Put the number of elements in key Y into integer register X.

=item toss_key Sx

Nuke key X. Throws the structure away and invalidates the register.

=item ke_type Ix, ky, iz

Put the type of key Y's entry Z in register X. Current values are 0,
1, and 2 for Integer, String, and PMC, respectively.

=item ke_value tx, ky, iz

Put the value from key Y, entry Z into register X.

=item chop_key Sx

Toss the topmost entry from key X.

=item inc_key Sx, iy

Increment entry Y of key X by one.

=item set_key Sw, [isp]x, iy[, iz]

Set key W, offset Y, to value X. If X is a PMC, then the fourth
operand must be specified. It can have a value of 0, 1, or 2,
corresponding to integer, string, or object. Aggregates use this to
figure out how to treat the key entry.

=back

=head2 Symbolic support for HLLs

=over 4

=item setline ix

Sets the 'current line' marker.

=item setfile sx

Sets the 'current file' marker.

=item setpackage sx

Sets the 'current package' marker.

=item getline ix

Fetches the 'current line' marker.

=item getfile sx

Fetches the 'current file' marker.

=item getpackage sx

Fetches the 'current package' marker.

=back

=head1 ATTACHMENTS

=head1 REFERENCES

