Trait Config

pub trait Config {
    const MAX_VALUE_STACK_SIZE: usize = 983_040usize;
    const MAX_CALL_STACK_SIZE: usize = 4_096usize;

    // Provided methods
    fn instruction_hook(&mut self, bytecode: &[u8], pc: usize) { ... }
    fn get_flat_cost(_instr: u8) -> u32 { ... }
    fn get_fc_extension_flat_cost(_instr: u32) -> u32 { ... }
    fn get_fd_extension_flat_cost(_instr: u32) -> u32 { ... }
    fn get_cost_per_element(_instr: u8) -> u32 { ... }
    fn get_fc_extension_cost_per_element(_instr: u32) -> u32 { ... }
}

Trait that allows user specified configuration for various items during interpretation. Additionally, the types implementing this trait can act as custom user data within an interpreter instance, passed along to each method of this trait and host functions whenever they are invoked.

The default implementation of all trait methods have the least overhead, i. e. most can be optimized out fully.

Provided Associated Constants

const MAX_VALUE_STACK_SIZE: usize = 983_040usize

Maximum number of values in the value stack

const MAX_CALL_STACK_SIZE: usize = 4_096usize

Maximum number of cascading function invocations

Provided Methods

fn instruction_hook(&mut self, bytecode: &[u8], pc: usize)

A hook which is called before every wasm instruction

This allows the most intricate insight into the interpreters behavior, at the cost of a hefty performance penalty

fn get_flat_cost(_instr: u8) -> u32

Amount of fuel to be deducted when a single byte instr is hit. The cost corresponding to UNREACHABLE and END instructions and other bytes that do not correspond to any Wasm instruction are ignored.

fn get_fc_extension_flat_cost(_instr: u32) -> u32

Amount of fuel to be deducted when a multi-byte instruction that starts with the byte 0xFC is hit. This method should return the cost of an instruction obtained by prepending 0xFC to of an unsigned 32-bit LEB representation of instr. Multi-byte sequences obtained this way that do not correspond to any Wasm instruction are ignored.

fn get_fd_extension_flat_cost(_instr: u32) -> u32

Amount of fuel to be deducted when a multi-byte instruction that starts with the byte 0xFD is hit. This method should return the cost of an instruction obtained by prepending 0xFD to of an unsigned 32-bit LEB representation of instr. Multi-byte sequences obtained this way that do not correspond to any Wasm instruction are ignored.

fn get_cost_per_element(_instr: u8) -> u32

Amount of fuel to be deducted per element of a single byte instruction instr that executes in asymptotically linear time with respect to one of the values it pops from the stack.

In Wasm 2.0 specification, this applies to the following instructions:

• MEMORY.GROW of type [n: i32] -> [i32]

The cost of the instruction is calculated as cost := get_flat_cost(instr) + n*get_cost_per_element(instr). where n is the stack value marked in the instruction type signature above. Other instructions and bytes that do not correspond to any instruction are ignored.

fn get_fc_extension_cost_per_element(_instr: u32) -> u32

Amount of fuel to be deducted per element of a multi-byte instruction that starts with the byte 0xFC, which executes in asymptotically linear time with respect to one of the values it pops from the stack. This method should return the cost of an instruction obtained by prepending 0xFD to of an unsigned 32-bit LEB representation of instr. Multi-byte sequences obtained this way that do not correspond to any Wasm instruction are ignored.

In Wasm 2.0 specification, this applies to the following instructions:

• MEMORY.INIT x of type [d:i32 s: i32 n: i32] -> []
• MEMORY.FILL of type [d: i32 val: i32 n: i32] -> []
• MEMORY.COPY of type [d: i32 s: i32 n: i32] -> []
• TABLE.GROW x of type [val: ref n: i32] -> [i32]
• TABLE.INIT x y of type [d: i32 s: i32 n: i32] -> []
• TABLE.FILL x of type [i: i32 val: ref n: i32] -> []
• TABLE.COPY x y of type [d: i32 s: i32 n: i32] -> []

The cost of the instruction is calculated as cost := get_flat_cost(instr) + n*get_cost_per_element(instr). where n is the stack value marked in the instruction type signature above. Other instructions and multi-byte sequences that do not correspond to any instruction are ignored.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl Config for ()

Default implementation of the interpreter configuration, with all hooks empty

Implementors