feat: add LOOKUP_DELEGATED_ADDRESS precompile wrapper by pali101 · Pull Request #6 · filecoin-project/fvm-solidity

pali101 · 2026-01-25T14:32:54Z

Summary

Implements the LOOKUP_DELEGATED_ADDRESS precompile wrapper (0xfe...02) to retrieve an actor's delegated address (f4) and extract the Ethereum-style address using optimized inline assembly.

Key Changes

Library: Added FVMLookupDelegatedAddress with:
- lookupDelegatedAddress(uint64) → bytes: Retrieves the raw delegated address. Handles the "success with no data" case for actors without a delegated address.
- lookupDelegatedAddressStrict(uint64) → bytes: Reverts with NoDelegatedAddress() if the lookup returns empty.
- toEthAddress(bytes) → address: Validates the f410 format (length 22, prefix 0x040a) and extracts the last 20 bytes as a standard Ethereum address.
Mocks:
- Added src/mocks/FVMLookupDelegatedAddress.sol which mirrors FVM behavior, including $uint64$ boundary checks.
- Updated MockFVMTest.sol to etch the precompile and expose LOOKUP_ADDR for low-level testing.
Tests: Added LookupDelegatedAddress.t.sol with coverage, including:
- Standard and Strict resolution.
- Fuzzed Ethereum address extraction.
- Boundary checks for Actor ID 0 and $max$ $uint64$.
- Validation of invalid prefixes and incorrect lengths.

Closes #2

Implement a library to wrap the LookupDelegatedAddress precompile

wjmelements · 2026-01-26T06:39:05Z

src/FVMLookupDelegatedAddress.sol

+
+import {LOOKUP_DELEGATED_ADDRESS} from "./FVMPrecompiles.sol";
+
+library FVMLookupDelegatedAddress {


library FVMActor

wjmelements · 2026-01-26T06:41:22Z

src/FVMLookupDelegatedAddress.sol

+
+            // Update free memory pointer
+            // Round up to nearest 32-byte boundary
+            let newFmp := add(add(delegatedAddress, 0x20), and(add(returnSize, 0x1f), not(0x1f)))


can we assume delegated addresses are all the same length?

wjmelements · 2026-01-26T06:46:40Z

src/mocks/FVMLookupDelegatedAddress.sol

+        uint256 actorIdFull = abi.decode(msg.data, (uint256));
+
+        // Validate that actor ID fits in u64 (max u64 = 2^64 - 1)
+        require(actorIdFull <= type(uint64).max, "Invalid actor ID: exceeds max u64");


Do these errors match the ones in builtin-actors?

wjmelements · 2026-01-26T06:47:26Z

src/mocks/FVMLookupDelegatedAddress.sol

+    /// @notice Mock a delegated address lookup
+    /// @param actorId The actor ID
+    /// @param delegatedAddress The delegated address to return (empty bytes means no delegated address)
+    function mockLookupDelegatedAddress(uint64 actorId, bytes memory delegatedAddress) external {


also provide a function to mock with solidity address.

wjmelements · 2026-01-26T06:50:56Z

src/Demo.sol

+    using FVMLookupDelegatedAddress for bytes;
+
+    /// @notice Lookup the delegated address of an actor ID
+    function lookup(uint64 actorId) external view returns (bytes memory delegatedAddress) {


please deploy one of these to calibration and link it in the PR

wjmelements · 2026-01-26T06:52:18Z

src/FVMLookupDelegatedAddress.sol

+            // Handle execution failure
+            if iszero(success) {
+                mstore(0, errorSelector)
+                revert(0, 4)


this won't work because the error would be at 28..32 after mstore. Instead, revert(28, 4).

wjmelements · 2026-01-26T06:52:39Z

src/FVMLookupDelegatedAddress.sol

+            let success := staticcall(gas(), LOOKUP_DELEGATED_ADDRESS, fmp, 32, 0, 0)
+
+            // Handle execution failure
+            if iszero(success) {


Is this possible?

wjmelements · 2026-01-26T06:53:23Z

src/FVMLookupDelegatedAddress.sol

+    /// @dev Validates that the address is 22 bytes and starts with 0x040a
+    /// @param delegatedAddress The delegated address (f410 format)
+    /// @return ethAddress The Ethereum-style address (last 20 bytes)
+    function toEthAddress(bytes memory delegatedAddress) internal pure returns (address ethAddress) {


move to separate library such as FVMAddress

wjmelements · 2026-01-26T06:54:57Z

test/LookupDelegatedAddress.t.sol

+        assertEq(result, expected, "Extracted address should match");
+    }
+
+    function testToEthAddressInvalidLength() public {


move toEthAddress tests to separate test file

wjmelements · 2026-01-26T06:55:23Z

src/FVMLookupDelegatedAddress.sol

+            // Shift right 240 bits (30 bytes) to get first 2 bytes
+            if iszero(eq(shr(240, firstWord), 0x040a)) {
+                mstore(0, errorSelector)
+                revert(0, 4)


revert(28, 4)

I had to test this to be sure! It looks like because errorSelector is passed in as a Solidity bytes4, it actually gets left-aligned on the stack. That puts it at the very beginning of the memory word, making revert(0, 4) the correct offset here.

If we were using a raw Yul literal inside the assembly block, you'd be exactly right with revert(28, 4).

Quick test to confirm

revert(0, 4) correctly returns the selector, while revert(28, 4) returns zeros.

error PrecompileCallFailed(); // Reverts with 0xfd23ff64 (PrecompileCallFailed) function rawStore() public pure returns (bytes32) { bytes4 selector = PrecompileCallFailed.selector; assembly ("memory-safe") { mstore(0, selector) revert(0,4) } } // Reverts with 0x00000000 function rawStore28() public pure returns (bytes32) { bytes4 selector = PrecompileCallFailed.selector; assembly ("memory-safe") { mstore(0, selector) revert(28,4) } }

That's pretty annoying because there is a difference in codesize and likely gas. Compare hardcoding the selector

I'll update the code to use the hardcoded selector (0x8eb60a41) and revert(28, 4). Just a heads up, I'm moving all this work to a new branch and will raise a fresh PR with all the comments addressed by tonight.

pali101 · 2026-03-01T17:29:19Z

Closing in favor of #9.
Since PR #5 completely restructured the library into FVMActor and FVMAddress, it was much cleaner to open a fresh branch than to fight the merge conflicts here. All of the feedback from this thread (#6) has been implemented in the new PR.

pali101 added 5 commits January 25, 2026 19:46

feat: add FVMLookupDelegatedAddress library

9138215

Implement a library to wrap the LookupDelegatedAddress precompile

feat: add FVMLookupDelegatedAddress mock contract

449730b

test: register lookup delegated address mock in MockFVMTest

2f0a4a6

docs: add lookupDelegatedAddress examples to Demo contract

476c3fe

test: add unit tests for LookupDelegatedAddress library

4749682

wjmelements mentioned this pull request Jan 26, 2026

feat: add RESOLVE_ADDRESS precompile wrapper #5

Merged

wjmelements requested changes Jan 26, 2026

View reviewed changes

wjmelements added the enhancement New feature or request label Feb 23, 2026

pali101 mentioned this pull request Mar 1, 2026

feat: add LOOKUP_DELEGATED_ADDRESS precompile wrapper #9

Open

pali101 closed this Mar 1, 2026


		import {LOOKUP_DELEGATED_ADDRESS} from "./FVMPrecompiles.sol";

		library FVMLookupDelegatedAddress {

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pali101 commented Jan 25, 2026

Summary

Key Changes

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Quick test to confirm

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pali101 commented Mar 1, 2026

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