memory.grow.md

memory.grow (request more memory)

Requests more memory be allocated to the WASM instance ¹.

Takes one operand from the stack, an i32 representing the number of pages to request ¹; Each page is defined as 64KiB ².

Returns one result to the stack, an i32 representing the previous total size of memory in pages, or -1 if the operation failed ¹.

$$ \mathsf{memory.grow} \enspace ( pages: \mathsf{i32} ) \to \begin{cases} -1_\mathsf{i32} &\text{if failed to grow} \\ \ge 0_\mathsf{i32} &\text{otherwise} \end{cases} $$

Instructions

Opcode	Instruction	Stack Arity
0x40	memory.grow	$[ \mathsf{i32} ] \to [ \mathsf{i32} ]$

WAT Examples

Requesting more memory

;; Places 2 on the stack
i32.const 2

;; Takes one value off of the stack (2), and requests
;; that many additional pages of memory
memory.grow

;; Places -1 on the stack
i32.const -1

;; Takes two values off of the stack (the result from
;; memory.grow and -1) and compares them
i32.eq

if
  ;; If the two values are equal, the instance failed
  ;; to get more memory
end

References

WebAssembly Core Specification

Footnotes

1. Structure, Memory Instructions - https://www.w3.org/TR/wasm-core-2/syntax/instructions.html#memory-instructions ↩ ↩² ↩³

2. Execution, Runtime Structure, Memory Instances - https://www.w3.org/TR/wasm-core-2/exec/runtime.html#memory-instances ↩