webalizer

Assembler that compiles to WebAssembly.

Metadata:

Status:

Stable, not reccomended for production.

Unsupported:

• System calls, planned to be bindable to JavaScript.

Installation:

Dependencies:

• capstone
• binaryen

Credits:

• @AlexAltea for capstone.js (dependency) and keystone.js (modified in source).
• AssemblyScript for Binaryen.js (dependency).

---

Usage:

import webalizer from "./src/index.js";

var buffer = [0x55, 0x31, 0xD2, 0x89, 0xE5, 0x8B, 0x45, 0x08];
var offset = 0x10000;

var module = webalizer(buffer, offset)

console.log(module.emitText()); // Output WAT

import webalizer from "./src/index.js";

var buffer = `
inc   rax;
call  0x10040;
mov   rax, qword ptr[rdx + 4];
sub   esp, 0x100;
pop   rbx;
` // x86 intel syntax is supported as a buffer.
var offset = 0x10000;

console.log(webalizer(buffer, offset).emitText());

Installing Dependencies:

• npm i

TODO:

• Goto
• Memory stack
• Memory values []
• Support for all x86 instructions
• Support for all x86 registers
• Functions
• Static data
• Use system calls to return, not default

Errors:

local.get index must be small enough

[wasm-validator error in function main] unexpected false: local.get index must be small enough, on 
(local.get $4294967295)
[wasm-validator error in function main] unexpected false: local.set index must be small enough, on 
(local.set $4294967295
 (local.get $4294967295)
)
Aborted(Assertion failed: index < base + vars.size(), at: /home/runner/work/binaryen.js/binaryen.js/binaryen/src/wasm/wasm.cpp,1314,isVar)

This error means that you are using an unsupported register that has not been mapped, resulting in the index being the maximum value of a 32 bit integer.

RuntimeError: Aborted(Assertion failed: *currp, at: /home/runner/work/binaryen.js/binaryen.js/binaryen/src/wasm-traversal.h,313,pushTask). Build with -sASSERTIONS for more info.

This is an internal error where generated WASM code is invalid, and should be reported to the issue tracker.

error: Capstone.js: Function cs_disasm failed with code 0: OK (CS_ERR_OK)

This error means that the buffer is not a Uint8Array or a ASM string, and should be converted to one. This can be done using new Uint8Array(buffer).

Architecture:

Files & Control Flow:

src/index.js - Main entry point.

• Take in a buffer, and an offset.
• If buffer is a string, compile it to a buffer using Keystone.
• Take the buffer and the offset and convert it to a list using Capstone.
• Create a main function for binaryen.
• Add the initial commands.
• Use omitter to visit instructions and add them to the main function.
• Add the return commands.
• Return the module.

src/omitter.js - Omitter.

• Take in a instruction and arguments.
• Use instructions.js to return Binaryen instructions.
• Expose functions for initializing and finishing the module.

src/ommiterfuncs.js - Omitter functions.

Functions used in the ommiter and in instructions, for example compiling an ASM Register to a WASM Local Index.

src/instructions.js - Instructions.

• Take in a instruction and arguments.
• Return a Binaryen instruction depending on the instruction and arguments.

src/data.js - Datas.

Holds constant data, for example the register names.

'src/keystone.min.js' - Keystone.

A modified version of keystone.js. Large file, do not directly modify.

Goto:

Since WASM does not support goto's we use a loop and a conditional to simulate a goto.