Instructions database and utilities for X86/X64 and ARM (THUMB/A32/A64) architectures.
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This is a public domain instruction-set database that contains the following architectures:

  • X86|X64 - Provided by x86data.js
  • A32|A64 - Provided by armdata.js

NOTE: There is currently work-in-progress to more standardize the database between various architectures, expect some data changes.

Data Files

Data files use .js suffix and are require()d and interepreted as JavaScript, however, these files are also parseable as JSON after locating JSON-BEGIN and JSON-END marks and stripping content outside of them. The database is meant to be readable and editable, thus it should stay small and simple.

The database provides the following concepts:

  • architectures
    • TODO: Better name
  • cpuLevels
    • TODO: Better name
  • extensions
    • List of available extensions, instructions can specify extension(s) in metadata
  • attributes
    • List of available attributes, instructions can specify attribute(s) in metadata
  • specialRegs
    • List of special registers (and their parts) that instructions can read/write to/from
  • shortcuts
    • List of shortcuts that can be used inside instruction's metadata, these shortcuts then expand to the expand key
  • registers
    • TODO: Better name and format
  • instructions
    • List of all instructions in a tuple format

X86 Data Files

X86 data provides the following information about each X86/X64 instruction:

  • Instruction name
  • Instruction operand(s):
    • Specifies always all possible operands for the given encoding & opcode
    • Operands can optionally contains a read/write information:
      • R: - The operand is read
      • W: - The operand is written
      • X: - The operand is read & written
      • W[A:B]: - Like W:, but specifies the first byte that is written (A) and how many bytes are written (B)
      • <...> - The operand (in most cases a register) is implicit and can be omitted
    • AVX-512 options:
      • {k} - Instruction supports write-masking
      • {kz} - Instruction supports write-masking by zeroing
      • {er} - Instruction supports embedded rounding control
      • {sae} - Instruction supports suppress-all-exceptions feature
  • Instruction encoding and opcode as specified in X86/X64 instruction-set manuals
  • Additional information that specifies:
    • Architecture required to encode / execute the instruction (ANY, X86, X64)
    • Extension(s) required to execute the instruction (MMX, SSE2, AVX2, ...)
    • Flags read/written by the instruction (CF, ZF, ... - R=Read, W=Written X=RW)
    • Prefixes that can be used before the instruction:
      • LOCK - Lock prefix can be used
      • REP - Rep prefix can be used
    • FPU (x87) flags:
      • FPU - The instruction is a FPU (x87) instruction
      • FPU_PUSH - The instruction pushes a value onto the FPU stack
      • FPU_POP - The instruction pops a value from the FPU stack
      • FPU_POP=2 - The instruction pops two values from the FPU stack
      • FPU_TOP=[+-]N - The instruction changes the top pointer of the FPU stack
    • Volatility - a hint for instruction reordering and scheduling
      • VOLATILE - The instruction must not be reordered
    • Privilege level:
      • PRIVILEGE=L[0-3] - The instruction's privilege level

Base API

The database itself provides a lot of information about each instruction, but since the DB is meant to be human readable and editable, the information presented is not in the best form to be processed as is. AsmDB solves this issue by providing API that can be used to index and query information stored in these data-files.

The API provides the following concepts:

  • ISA
    • Used to index and retrieve information located in architecture data-files
    • Provides ability to explore the ISA
    • Provides query interface that can be used to query only specific instructions
  • Instruction
    • Contains information about a single instruction, as specified in vendor-specific architecture reference manual.
  • Operand
    • Contains information about a single operand

AsmDB API probides base interfaces for these concepts, and each architecture then provides ISA-dependent versions of these.


AsmDB's asmdb.x86.ISA is the interface used to index and access the ISA. The following snippet shows a basic usage of it:

// Create the ISA instance populated by default x86 data.
const asmdb = require("asmdb");
const isa = new asmdb.x86.ISA();

// Returns an array of instruction names stored in the database:

// Iterates over all instructions in the database. Please note that instructions
// that have different operands but the same name (or different encodings) will
// appear multiple times as specified in the x86/x64 manuals. The `inst` is an
// `asmdb.x86.Instruction` instance.
isa.instructions.forEach(function(inst) {
  console.log(`Instruction '{}' [${inst.encoding}] ${inst.opcodeString}`);
}, this);

// Iterates over all instructions in the database, but groups instructions having
// the same name. It's similar to `instructions.forEach()`, but instead of providing
// a single instruction each time it provides an array of instructions sharing the
// same name.
isa.forEachGroup(function(name, insts) {
  console.log(`Instruction ${name}`:);
  for (var i = 0; i < insts.length; i++) {
    const inst = insts[i];
    console.log(`  [${inst.encoding}] ${inst.opcodeString}`);
}, this);

// If iterators are not what you want, it's possible to get a list of instructions
// of the same name by using `query()`.
var insts = isa.query("mov");
for (var i = 0; i < insts.length; i++) {
  const inst = insts[i];
  console.log(`  ${} [${inst.encoding}] ${inst.opcodeString}`);

// You can implement your own iterator by using `instruction`, `instructionNames`,
// `instructionMap`, or `query()`:
const names = isa.instructionNames;
for (var i = 0; i < names.length; i++) {
  const name = names[i];
  const insts = x86.query(name);
  // ...

The snippet above just shown how to get instructions and list basic properties. What is more interesting is accessing asmdb.x86.Instruction and asmdb.x86.Operand data.

const asmdb = require("asmdb");
const isa = new asmdb.x86.ISA();

// Get some instruction (the first in the group):
const inst = isa.query("vpunpckhbw")[0];
console.log(JSON.stringify(inst, null, 2));

// Iterate over its operands:
const operands = inst.operands;
for (var i = 0; i < operands.length; i++) {
  const operand = operands[i];
  // ...

The stringified instruction would print something like this (with added comments that describe the meaning of individual properties):

  "name": "vpunpckhbw",            // Instruction name.
  "arch": "ANY",                   // Architecture - ANY, X86, X64.
  "encoding": "RVM",               // Instruction encoding.
  "prefix": "VEX",                 // Prefix - "", "3DNOW", "EVEX", "VEX", "XOP".
  "opcode": "68",                  // A single opcode byte as a hex string, "00-FF".
  "opcodeInt": 104,                // A single opcode byte as an integer (0..255).
  "opcodeString":                  // The whole opcode string, as specified in manual.
    "VEX.NDS.128.66.0F.WIG 68 /r",
  "l": "128",                      // Opcode L field (nothing, 128, 256, 512).
  "w": "WIG",                      // Opcode W field.
  "pp": "66",                      // Opcode PP part.
  "mm": "0F",                      // Opcode MM[MMM] part.
  "vvvv": "NDS",                   // Opcode VVVV part.
  "_67h": false,                   // Instruction requires a size override prefix.
  "rm": "r",                       // Instruction specific payload "/0..7".
  "rmInt": -1,                     // Instruction specific payload as integer (0-7).
  "ri": false,                     // Instruction opcode is combined with register, "XX+r" or "XX+i".
  "rel": 0,                        // Displacement (cb cw cd parts).
  "implicit": false,               // Uses implicit operands (registers / memory).
  "privilege": "L3",               // Privilege level required to execute the instruction.
  "fpu": false,                    // True if this is an FPU instruction.
  "fpuTop": 0,                     // FPU top index manipulation [-1, 0, 1, 2].
  "vsibReg": "",                   // AVX VSIB register type (xmm/ymm/zmm).
  "vsibSize": -1,                  // AVX VSIB register size (32/64).
  "broadcast": false,              // AVX-512 broadcast support.
  "bcstSize": -1,                  // AVX-512 broadcast size.
  "kmask": false,                  // AVX-512 merging {k}.
  "zmask": false,                  // AVX-512 zeroing {kz}, implies {k}.
  "sae": false,                    // AVX-512 suppress all exceptions {sae} support.
  "rnd": false,                    // AVX-512 embedded rounding {er}, implies {sae}.
  "tupleType": "",                 // AVX-512 tuple-type.
  "elementSize": -1,               // Instruction element size (used by broadcast).

  // Extensions required to execute the instruction:
  "extensions": {
    "AVX": true                    // Instruction is an "AVX" instruction.

  // Instruction attributes
  "attributes": {

  // Special registers accessed by the instruction.
  "specialRegisters": {

  // Instruction operands:
  "operands": [{
    "data": "xmm",                 // The operand's data (processed).
    "reg": "xmm",                  // Register operand's definition.
    "regType": "xmm",              // Register operand's type (would differ if reg is "eax" for example).
    "mem": "",                     // Memory operand's definition.
    "memSize": -1,                 // Memory operand's size.
    "memOff": false,               // Memory operand is an absolute offset (only a specific version of MOV).
    "memSeg": "",                  // Segment specified with register that is used to perform a memory IO.
    "vsibReg": "",                 // AVX VSIB register type (xmm/ymm/zmm).
    "vsibSize": -1,                // AVX VSIB register size (32/64).
    "bcstSize": -1,                // AVX-512 broadcast size.
    "imm": 0,                      // Immediate operand's size.
    "immValue": null,              // Immediate value - `null` or `1` (only used by shift/rotate instructions).
    "rel": 0,                      // Relative displacement operand's size.
    "implicit": false,             // True if the operand is an implicit register (not encoded in binary).
    "read": false,                 // True if the operand is a read-op (R or X) from reg/mem.
    "write": true,                 // True if the operand is a write-op (W or X) to reg/mem.
    "rwxIndex": null,              // Read/Write (RWX) index.
    "rwxWidth": null               // Read/Write (RWX) width.
  }, {
    "data": "xmm",                 // ...
    "reg": "xmm",
    "regType": "xmm",
    "mem": "",
    "memSize": -1,
    "memOff": false,
    "memSeg": "",
    "vsibReg": "",
    "vsibSize": -1,
    "bcstSize": -1,
    "imm": 0,
    "immValue": null,
    "rel": 0,
    "implicit": false,
    "read": true,
    "write": false,
    "rwxIndex": -1,
    "rwxWidth": -1
  }, {
    "data": "xmm/m128",
    "reg": "xmm",
    "regType": "xmm",
    "mem": "m128",
    "memSize": 128,
    "memOff": false,
    "memSeg": "",
    "vsibReg": "",
    "vsibSize": -1,
    "bcstSize": -1,
    "imm": 0,
    "immValue": null,
    "rel": 0,
    "implicit": false,
    "read": true,
    "write": false,
    "rwxIndex": -1,
    "rwxWidth": -1

ARM Database