fix(revm): align BLOCKHASH with Morph geth semantics

[panos-xyz]

Summary

• align BLOCKHASH opcode in morph-revm with Morph geth semantics: return keccak(chain_id || block_number) in the last-256-block window
• keep Ethereum-compatible out-of-range behavior (0 for current/future/out-of-window requests)
• add focused unit tests for a golden vector (chain_id=2818, number=2662437) and 256-window boundary behavior

Why

• mainnet block 2662438 failed import with block gas used mismatch (got 823153, expected 825454)
• root cause was an opcode semantics mismatch on BLOCKHASH, which changed downstream execution path and gas accounting

Test plan

• cargo check -p morph-revm
• cargo test -p morph-revm morph_blockhash
• deploy validation completed on target environment (block import succeeds)

Closes #37

[coderabbitai]

📝 Walkthrough

Walkthrough

Implements Morph-specific BLOCKHASH opcode behavior in the EVM, including helper functions to compute keccak256-hashed block references and enforce the 256-block history window, with corresponding test coverage and instruction registration.

Changes

Cohort / File(s)	Summary
Morph BLOCKHASH Implementation crates/revm/src/evm.rs	Adds helper functions for saturating U256-to-u64 conversion and keccak256-based blockhash computation; implements blockhash_morph instruction to enforce Morph's 256-block history window (returning hashed values for valid blocks, zero otherwise); registers new instruction handler and adds comprehensive test coverage for boundary conditions and known test vectors.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

• bug: block gas used mismatch at block 2662438 on mainnet (BLOCKHASH semantics mismatch) #37 — Directly addresses Morph-specific BLOCKHASH implementation using keccak(chain_id||block_number) for the last-256 blocks, matching the changes in this PR.

Suggested reviewers

• anylots

Poem

🐰 A blockhash, hashed true, for Morph's embrace,
Two-hundred-fifty-six blocks in history's space,
Keccak whispers secrets of chain and block number,
Stack pops and pushes through EVM's grand thunder,
One instruction to rule them all! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix(revm): align BLOCKHASH with Morph geth semantics' directly and accurately summarizes the main change: implementing Morph-specific BLOCKHASH semantics in the revm crate.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/blockhash-morph-semantics

Tip

Try Coding Plans. Let us write the prompt for your AI agent so you can ship faster (with fewer bugs).
Share your feedback on Discord.

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

🧹 Nitpick comments (1)

crates/revm/src/evm.rs (1)

285-289: Strengthen the lower-bound test to assert exact value, not just non-zero.

Line 286 currently only proves “some non-zero value” was returned. Asserting equality against morph_blockhash_value(chain_id, current - 256) will catch hashing/input regressions too.

Suggested test tightening

-        // lower bound is inclusive (current - 256 is valid)
-        assert_ne!(
-            morph_blockhash_result(chain_id, current, current - 256),
-            U256::ZERO
-        );
+        // lower bound is inclusive (current - 256 is valid)
+        assert_eq!(
+            morph_blockhash_result(chain_id, current, current - 256),
+            morph_blockhash_value(chain_id, current - 256)
+        );

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@crates/revm/src/evm.rs` around lines 285 - 289, The test currently only
asserts the blockhash is non-zero using morph_blockhash_result(chain_id,
current, current - 256); replace that non-zero check with an exact equality
assertion against the expected value by calling morph_blockhash_value(chain_id,
current - 256) and asserting morph_blockhash_result(chain_id, current, current -
256) == morph_blockhash_value(chain_id, current - 256) so the test fails on any
hashing/input regression.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@crates/revm/src/evm.rs`:
- Around line 285-289: The test currently only asserts the blockhash is non-zero
using morph_blockhash_result(chain_id, current, current - 256); replace that
non-zero check with an exact equality assertion against the expected value by
calling morph_blockhash_value(chain_id, current - 256) and asserting
morph_blockhash_result(chain_id, current, current - 256) ==
morph_blockhash_value(chain_id, current - 256) so the test fails on any
hashing/input regression.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: db784831-6f4c-422d-9a3a-300cc571598e

📥 Commits

Reviewing files that changed from the base of the PR and between 74c1a9c and a0a33a9.

📒 Files selected for processing (1)

• crates/revm/src/evm.rs