From 1ca17b9880b6df72dd877579c8ff18e33e7b84f2 Mon Sep 17 00:00:00 2001
From: Marc Harvey-Hill <Marchhill@users.noreply.github.com>
Date: Fri, 16 May 2025 17:54:11 +0100
Subject: [PATCH 1/2] implement asserttxindex instruction

---
 src/ethereum/prague/vm/instructions/system.py | 31 ++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/ethereum/prague/vm/instructions/system.py b/src/ethereum/prague/vm/instructions/system.py
index ea9be98391..483237017b 100644
--- a/src/ethereum/prague/vm/instructions/system.py
+++ b/src/ethereum/prague/vm/instructions/system.py
@@ -48,6 +48,7 @@
     GAS_NEW_ACCOUNT,
     GAS_SELF_DESTRUCT,
     GAS_SELF_DESTRUCT_NEW_ACCOUNT,
+    GAS_VERY_LOW,
     GAS_WARM_ACCESS,
     GAS_ZERO,
     calculate_gas_extend_memory,
@@ -56,7 +57,7 @@
     init_code_cost,
     max_message_call_gas,
 )
-from ..memory import memory_read_bytes, memory_write
+from ..memory import buffer_read, memory_read_bytes, memory_write
 from ..stack import pop, push
 
 
@@ -742,3 +743,31 @@ def revert(evm: Evm) -> None:
 
     # PROGRAM COUNTER
     pass
+
+def asserttxindex(evm: Evm) -> None:
+    """
+	Reverts if expected transaction index does not match actual transaction
+    index, or if not executed at the start of a transaction (after PUSHN).
+    Parameters
+    ----------
+    evm :
+        The current EVM frame.
+    """
+    # STACK
+    start_index = pop(evm.stack)
+
+    # GAS
+    charge_gas(evm, GAS_VERY_LOW)
+
+    # OPERATION
+    expected_tx_index = U256(buffer_read(evm.message.data, start_index, U256(32)))
+
+    if evm.message.depth != 0 or\
+       evm.message.gas - evm.gas_left > 2 * GAS_VERY_LOW or\
+       evm.message.tx_env.index_in_block is None or\
+       expected_tx_index != evm.message.tx_env.index_in_block and expected_tx_index != U256(-1):
+	    # assertion failed
+        raise Revert
+
+    # PROGRAM COUNTER
+    evm.pc += Uint(1)

From 7ea9db51ed8b64ebaca706f6b559a2b6ab655d61 Mon Sep 17 00:00:00 2001
From: Marc Harvey-Hill <Marchhill@users.noreply.github.com>
Date: Fri, 16 May 2025 18:02:40 +0100
Subject: [PATCH 2/2] enable opcode

---
 src/ethereum/prague/vm/instructions/__init__.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/ethereum/prague/vm/instructions/__init__.py b/src/ethereum/prague/vm/instructions/__init__.py
index b220581c72..91ffd1b903 100644
--- a/src/ethereum/prague/vm/instructions/__init__.py
+++ b/src/ethereum/prague/vm/instructions/__init__.py
@@ -210,6 +210,7 @@ class Ops(enum.Enum):
     DELEGATECALL = 0xF4
     CREATE2 = 0xF5
     STATICCALL = 0xFA
+    ASSERTTXINDEX = 0xFB
     REVERT = 0xFD
     SELFDESTRUCT = 0xFF
 
@@ -363,4 +364,5 @@ class Ops(enum.Enum):
     Ops.STATICCALL: system_instructions.staticcall,
     Ops.REVERT: system_instructions.revert,
     Ops.CREATE2: system_instructions.create2,
+	Ops.ASSERTTXINDEX: system_instructions.asserttxindex,
 }