mips-assembler

Simple MIPS IV assembler for JavaScript.

The features that are included are compatible with armips, when possible. armips is much more sophisticated currently though.

Usage

import { assemble } from "mips-assembler";

assemble(`
  .org 0x80050000

  .definelabel ExternalPtr,0x8033C000
  .definelabel ExternalLibFn,0x80104321

  ADDIU SP SP 0xFFE0
  SW RA 0x18(SP)

  loop:
  LUI A0 hi(ExternalPtr)
  JAL ExternalLibFn
  ADDIU A0 A0 lo(ExternalPtr)
  BEQ V0 R0 loop
  NOP

  LW RA 0x18(SP)
  JR RA
`)
// ArrayBuffer<
//   27BDFFE0  ADDIU SP SP 0xFFE0
//   AFBF0018  SW RA 0x18(SP)
//   3C048034  LUI A0 0x8034
//   0C0410C8  JAL 0x80104321
//   2484C000  ADDIU A0 A0 0xC000
//   1040FFFD  BEQ V0 R0 -3
//   00000000  NOP
//   8FBF0018  LW RA 0x18(SP)
//   03E00008  JR RA
// >

The default return value is an ArrayBuffer.

An opts object can be passed as the second parameter. It can contain various properties to affect behavior.

| Option | Description | |---|---| | buffer | (ArrayBuffer) When passed, assembly will be performed on the given buffer, rather than creating a new buffer. | | files | (Object) Used with the include file directive, see below. | | text | (String) Output will be instructions in text format, similar to the format shown beside the ArrayBuffer above. | | symbolOutputMap | (Object) If you pass an object on this property, it will be filled with a map from symbol name to the output location of that symbol.For example, if you labeled a .word as my_number and that number was output to buffer offset 0x100, the symbolOutputMap would be { "my_number": 0x100 }. |

The UMD module in dist/umd exports a MIPSAssem global.

Features

Labels

Labels can be used to reference locations by name. Labels are global by default.

main:
    ADDIU SP SP -32
    ...
loop:
    JAL 0x80023456
    ...

They can be on their own line, or on the same line as other instructions or labels. Labels can contain letters, numbers, underscores, ? or !.

main:
main2: start: ADDIU SP SP -32
    ...
loop?!: JAL 0x80023456
    ...

If a label starts with @@, it is a local label and only can be defined and used in the area between the two nearest global labels.

; The example from armips...
GlobalLabel:       ; This is a global label
@@LocalLabel:      ; This is a local label, it is only
                   ; valid until the next global one
OtherGlobalLabel:  ; this will terminate the area where
                   ; @@LocalLabel can be used
j @@LocalLabel     ; as a result, this will cause an error

If a label starts with a single @, it is a static label. Static labels act like global labels, but are only visible to the current "file." See the include or beginfile/endfile directives.

Directives

General directives

Set the memory position

.org RamAddress

Adjusts the working memory location the assembly. This affects individual instructions, but not the locations where they are outputted.

Set the output position

.orga BufferOffset

Sets the output pointer to the specified offset. This affects the location that subsequent instructions are written to, but doesn't affect individual instructions.

Create labels

.definelabel label,value

Defines label with a given value, creating a symbol for it.

Include another assembly file

.include "filename"

Inlines a "file" containing assembly at the current location.

Note that, since we're in JavaScript, the "filename" is not a path to an actual file. It should be a key in the files object that can be passed through the assemble opts.

assemble(`
  .org 0x80001000
  .include "external"
`, {
  files: {
    "external": `
      ADDIU A0 R0 123
      .ascii "This is the external 'file'"
    `
  }
});

File scoping

.beginfile
.endfile

If you want to achieve file scoping without actually having separate assembly in the files opt object, you can surround assembly with .beginfile and .endfile. This would enable usage of static labels for example.

equ

Limited support is available for equ direct text replacements.

NumList equ 1,2,3,4

.word NumList

As with regular symbols, these are global replacements by default. A single leading @ creates a static replacement, and two leading @@ creates a local replacement.

Text and data directives

Align the output position

.align num

Writes zeros into the output file until the output position is a multiple of num. num has to be a power of two.

Fill space with a value

.fill length[,value]

Inserts length amount of bytes of value. If value isn't specified, zeros are inserted. Only the lowest 8 bits of value are inserted.

Skip bytes

.skip length

Skips length amount of bytes without overwriting them.

Write bytes

.byte value[,...]
.db value[,...]

Writes a sequence of bytes. Only the lowest 8 bits are inserted.

Write halfwords

.halfword value[,...]
.dh value[,...]

Writes a sequence of 16-bit values. Only the lowest 16 bits are inserted.

Write words

.word value[,...]
.dw value[,...]

Writes a sequence of 32-bit values. Only the lowest 32 bits are inserted.

Write floating point numbers

.float value[,...]

Writes a sequence of single-precision floats.

Write text

.ascii value[,...]
.asciiz value[,...]

Writes a sequence of characters or bytes. Each parameter can be any expression that evaluates to an integer or a string. If it evaluates to an integer, only the lowest 8 bits are inserted. If it evaluates to a string, every character is inserted as a byte.

With asciiz, a single null terminator is inserted after the values.

Conditional directives

Begin a conditional block

.if cond

The content of a conditional block will only be used if the condition is met. In the case of .if, it is met of cond evaluates to non-zero integer.

Else case of a conditional block

.else
.elseif cond

The else block is used if the condition of the condition of the if block was not met. .else unconditionally inserts the content of the else block, while the others start a new if block and work as described before.

End a conditional block

.endif

Ends the last open if or else block.

Macros

Also known as "pseudo-instructions."

Immediate macros

li reg,value

Loads the value into the specified register using the appropriate combination of lui, addiu, or ori.

Register macros

move dest,reg

Copies the contents of reg into dest using an addu.

Branch macros

beqz  reg,dest
bnez  reg,dest
bnezl reg,dest

Built-in functions

These functions can be used in place of immediates, and can be passed symbols/labels instead of just immediates.

| Function | Description | |----------|-------------| | abs(value) | Absolute value of value | | hi(value) | High half of 32-bit value value, adjusted for sign extension of low half | | lo(value) | Sign-extended low half of 32-bit value value | | org() | Current memory address |

Comments

Both ; and // single-line comments are supported. /* */ block comments are also supported.

Development

To build:

npm install
npm run build

To run tests:

npm run test

License

MIT