WebAssembly support
Features
The following features are available, in addition to WebAssembly MVP:
Implementation Limits
A WebAssembly module must obey several constraints, which are defined by a VMOptions object, which is loaded at the start of the transaction from the transactionWasmConfigTable or proofWasmConfigTable depending on the context in which it is being run. These constraints serve to limit the temporary memory required to run the transaction.
Max stack bytes
Every function is assigned a cost which is calculated as the total size of all local variables, all stack items, and the call frame. Function parameters are counted in the caller, not the callee. Since the stack varies throughout the function, we use the maximum size of the stack at any point in the function.
| Type | Size |
|---|---|
i32 | 4 |
f32 | 4 |
i64 | 8 |
f64 | 8 |
v128 | 16 |
| frame | 16 |
call has a cost of 4096. All other host functions have a cost of 0.
If the total cost of all functions on the stack ever exceeds the configured limit, the transaction will terminate with an error. In addition, if any function has a cost greater than 128 MiB, the module will fail to validate (No reasonable module can exceed this limit, because it requires having unused locals).
Max pages
memory.grow fails and returns -1 if it is asked to increase the number of 64 KiB pages past the configured limit. If a module's initial memory exceeds the limit, the module will fail to load.
Max table elements
If the initial size of the table is greater than the limit, the module will fail to load.
Max mutable global bytes
If the total size of all mutable globals is greater than the limit, the module will fail to load.
Module size
A module must fit in a database row, which means that it cannot be larger than 8 MiB in toto.