From 90fa38654803291e8b4f1306381aec54a34a9b2d Mon Sep 17 00:00:00 2001
From: Robin Salen <30937548+Nashtare@users.noreply.github.com>
Date: Tue, 27 Feb 2024 08:33:33 +0900
Subject: [PATCH] Fix trace decoder padding with dummy payloads (#63)

* Fix trace decoder padding with dummy payloads

* Add CHANGELOG entry
---
 CHANGELOG.md                  |  1 +
 trace_decoder/src/decoding.rs | 15 +++++++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index fcaef8b36..af95f6fd5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add verification for invalid jumps. [#36](https://github.com/0xPolygonZero/zk_evm/pull/36)
 - Refactor accessed lists as sorted linked lists ([#30](https://github.com/0xPolygonZero/zk_evm/pull/30))
 - Change visibility of `compact` mod ([#57](https://github.com/0xPolygonZero/zk_evm/pull/57))
+- Fix block padding without withdrawals ([#63](https://github.com/0xPolygonZero/zk_evm/pull/63))
 
 ## [0.1.0] - 2024-02-21
 * Initial release.
diff --git a/trace_decoder/src/decoding.rs b/trace_decoder/src/decoding.rs
index 482918b56..9190f13af 100644
--- a/trace_decoder/src/decoding.rs
+++ b/trace_decoder/src/decoding.rs
@@ -102,6 +102,9 @@ impl ProcessedBlockTrace {
             gas_used_after: U256::zero(),
         };
 
+        // A copy of the initial extra_data possibly needed during padding.
+        let extra_data_for_dummies = extra_data.clone();
+
         let mut txn_gen_inputs = self
             .txn_info
             .into_iter()
@@ -156,6 +159,7 @@ impl ProcessedBlockTrace {
             &mut txn_gen_inputs,
             &other_data,
             &extra_data,
+            &extra_data_for_dummies,
             &initial_tries_for_dummies,
             &curr_block_tries,
             !self.withdrawals.is_empty(),
@@ -303,7 +307,8 @@ impl ProcessedBlockTrace {
     fn pad_gen_inputs_with_dummy_inputs_if_needed(
         gen_inputs: &mut Vec<TxnProofGenIR>,
         other_data: &OtherBlockData,
-        extra_data: &ExtraBlockData,
+        final_extra_data: &ExtraBlockData,
+        initial_extra_data: &ExtraBlockData,
         initial_tries: &PartialTrieState,
         final_tries: &PartialTrieState,
         has_withdrawals: bool,
@@ -311,10 +316,11 @@ impl ProcessedBlockTrace {
         match gen_inputs.len() {
             0 => {
                 debug_assert!(initial_tries.state == final_tries.state);
+                debug_assert!(initial_extra_data == final_extra_data);
                 // We need to pad with two dummy entries.
                 gen_inputs.extend(create_dummy_txn_pair_for_empty_block(
                     other_data,
-                    extra_data,
+                    final_extra_data,
                     initial_tries,
                 ));
 
@@ -330,11 +336,12 @@ impl ProcessedBlockTrace {
                 match has_withdrawals {
                     false => {
                         let dummy_txn =
-                            create_dummy_gen_input(other_data, extra_data, initial_tries);
+                            create_dummy_gen_input(other_data, initial_extra_data, initial_tries);
                         gen_inputs.insert(0, dummy_txn)
                     }
                     true => {
-                        let dummy_txn = create_dummy_gen_input(other_data, extra_data, final_tries);
+                        let dummy_txn =
+                            create_dummy_gen_input(other_data, final_extra_data, final_tries);
                         gen_inputs.push(dummy_txn)
                     }
                 };