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WASM Runtime

The delegated WASM runtime dispatches calls and creates targeting Wasm contracts. Init code starting with the WASM magic preamble is routed here at deploy time.

Address​

ConstantAddress
PRECOMPILE_WASM_RUNTIME0x0000000000000000000000000000000000520009

Routing​

Init code starting with WASM_MAGIC_BYTES = 0x0061736d (the standard Wasm 4-byte preamble) routes to this runtime. The dispatcher logic lives in resolve_precompiled_runtime_from_input in fluentbase/crates/types/src/genesis.rs. Direct calls to the runtime address are rejected.

Behavior​

deploy_entry compiles the input Wasm to rWasm via RwasmModule::compile, validates the result against RWASM_MAX_CODE_SIZE = 12 MiB, and returns the compiled module plus any constructor parameters. Compilation is metered:

WASM_COMPILATION_OVERHEAD_FUEL_PER_BYTE = 50 * FUEL_DENOM_RATE = 1000 fuel/byte = 50 gas/byte

A 100 KB Wasm payload pays roughly 5,000,000 gas just to compile. Estimate deploy cost accordingly.

After compilation, the executor installs the rWasm bytes at the deployed address (replacing the temporary ownable wrapper). The account's code field then starts with the rWasm magic prefix 0xEF52, and subsequent calls execute the rWasm directly at that address — main_entry on this dispatcher returns UnreachableCodeReached and is never hit on a properly deployed contract. See the wrapper-rewrite path in Runtime Routing and Ownable Accounts.

Errors​

  • MalformedBuiltinParams — RwasmModule::compile rejected the input.
  • CreateContractSizeLimit — compiled rWasm exceeds RWASM_MAX_CODE_SIZE.
  • UnreachableCodeReached — only path through main_entry; should not be reached on a properly deployed contract.

Metadata syscalls and Wasm contracts​

Metadata syscalls operate only on Bytecode::OwnableAccount. Because Wasm contracts are stored as Bytecode::Rwasm after the deploy rewrite, the syscalls behave as follows when called against a Wasm contract:

  • METADATA_SIZE returns size = 0 (graceful, no halt).
  • METADATA_ACCOUNT_OWNER returns Address::ZERO (graceful, no halt).
  • METADATA_WRITE and METADATA_COPY halt with MalformedBuiltinParams.

Source​

fluentbase/contracts/wasm/