Exec Mode Features

Native WASM Interpreter

A self-hosted WebAssembly interpreter written in Rust. No external runtime dependency — the interpreter is part of the wasmrun binary.

Instruction Support

Category	Instructions	Status
i32 arithmetic	add, sub, mul, div, rem, clz, ctz, popcnt	✅ Complete
i64 arithmetic	add, sub, mul, div, rem, clz, ctz, popcnt	✅ Complete
f32 arithmetic	add, sub, mul, div, sqrt, min, max, ceil, floor, trunc, nearest, abs, neg, copysign	✅ Complete
f64 arithmetic	add, sub, mul, div, sqrt, min, max, ceil, floor, trunc, nearest, abs, neg, copysign	✅ Complete
Comparison	eq, ne, lt, gt, le, ge (all types, signed/unsigned)	✅ Complete
Logic	and, or, xor, shl, shr, rotl, rotr (i32/i64)	✅ Complete
Memory	load, store (all widths: 8/16/32/64, signed/unsigned), memory.size, memory.grow	✅ Complete
Control flow	block, loop, if/else, br, br_if, br_table, return, call, call_indirect, select, nop, unreachable	✅ Complete
Variables	local.get/set/tee, global.get/set	✅ Complete
Type conversions	wrap, extend, trunc, convert, demote, promote, reinterpret	✅ Complete
Data sections	Active data segment initialization into linear memory	✅ Complete

Linear Memory

• 64KB pages with configurable initial and max sizes
• Bounds checking on every access
• Little-endian byte order (WASM standard)
• Support for memory.grow

WASI Preview 1

Basic WASI syscall support for system interaction:

• fd_write — write to stdout/stderr
• fd_read — read from stdin
• environ_get / environ_sizes_get — environment variables
• args_get / args_sizes_get — command-line arguments
• clock_time_get — real-time and monotonic clocks
• random_get — random bytes
• proc_exit — process exit

Entry Point Detection

The executor automatically finds the entry point by checking (in order):

1. Start section — WASM module's designated start function
2. _start export — WASI convention
3. main export — common convention

Or you can specify a function explicitly with --call.

Argument Passing

Arguments are parsed and converted to WASM values:

• Integer strings → Value::I32 or Value::I64
• Everything else → Value::I32(0) (fallback)

Arguments are also available to the WASM program via WASI's args_get syscall.

Function Selection

Call any exported function by name:

wasmrun exec ./math.wasm --call multiply 6 7

The executor looks up the export, validates the signature, and invokes it with the provided arguments.