feat(kernel): expose tx script root via public kernel procedure

CHANGELOG.md

@@ -21,6 +21,7 @@
 - [BREAKING] Added cycle counts to notes returned by `NoteConsumptionInfo` and removed public fields from related types ([#2772](https://github.com/0xMiden/miden-base/issues/2772)).
 - [BREAKING] Removed unused `payback_attachment` from `SwapNoteStorage` and `attachment` from `MintNoteStorage` ([#2789](https://github.com/0xMiden/protocol/pull/2789)).
 - Automatically enable `concurrent` feature in `miden-tx` for `std` context ([#2791](https://github.com/0xMiden/protocol/pull/2791)).
+- Added `tx::get_tx_script_root` kernel procedure returning the root of the executed transaction script (zero word if no script was executed) ([#2816](https://github.com/0xMiden/protocol/pull/2816)).
 - Added `TransactionScript::from_package()` method to create `TransactionScript` from `miden-mast-package::Package` ([#2779](https://github.com/0xMiden/protocol/pull/2779)).
 
 ### Fixes

crates/miden-protocol/asm/kernels/transaction/api.masm

@@ -1323,6 +1323,26 @@ pub proc tx_get_num_input_notes
     # => [num_input_notes, pad(15)]
 end
 
+#! Returns the transaction script root.
+#!
+#! Inputs:  [pad(16)]
+#! Outputs: [TX_SCRIPT_ROOT, pad(12)]
+#!
+#! Where:
+#! - TX_SCRIPT_ROOT is the transaction script root, or the zero word if no transaction script was
+#!   executed.
+#!
+#! Invocation: dynexec
+pub proc tx_get_tx_script_root
+    # get the tx script root
+    exec.tx::get_tx_script_root
+    # => [TX_SCRIPT_ROOT, pad(16)]
+
+    # truncate the stack
+    swapw dropw
+    # => [TX_SCRIPT_ROOT, pad(12)]
+end
+
 #! Returns the current number of output notes created in this transaction.
 #!
 #! Inputs:  [pad(16)]

crates/miden-protocol/asm/kernels/transaction/lib/memory.masm

@@ -660,6 +660,18 @@ pub proc set_tx_script_root
     mem_storew_le.TX_SCRIPT_ROOT_PTR
 end
 
+#! Returns the transaction script root.
+#!
+#! Inputs:  []
+#! Outputs: [TX_SCRIPT_ROOT]
+#!
+#! Where:
+#! - TX_SCRIPT_ROOT is the transaction script root, or the zero word if no transaction script was
+#!   executed.
+pub proc get_tx_script_root
+    padw mem_loadw_le.TX_SCRIPT_ROOT_PTR
+end
+
 #! Returns the transaction script arguments.
 #!
 #! Inputs:  []

crates/miden-protocol/asm/kernels/transaction/lib/tx.masm

@@ -85,6 +85,16 @@ pub use memory::get_num_input_notes
 #! - num_output_notes is the number of output notes created in this transaction so far.
 pub use memory::get_num_output_notes
 
+#! Returns the transaction script root.
+#!
+#! Inputs:  []
+#! Outputs: [TX_SCRIPT_ROOT]
+#!
+#! Where:
+#! - TX_SCRIPT_ROOT is the transaction script root, or the zero word if no transaction script was
+#!   executed.
+pub use memory::get_tx_script_root
+
 #! Updates the transaction expiration block delta.
 #!
 #! The input block_height_delta is added to the block reference number in order to output an upper

crates/miden-protocol/asm/protocol/kernel_proc_offsets.masm

@@ -89,3 +89,6 @@ pub const TX_EXEC_FOREIGN_PROC_OFFSET = 48
 # expiration data
 pub const TX_GET_EXPIRATION_DELTA_OFFSET=49               # accessor
 pub const TX_UPDATE_EXPIRATION_BLOCK_DELTA_OFFSET=50      # mutator
+
+# tx script
+pub const TX_GET_TX_SCRIPT_ROOT_OFFSET=51

crates/miden-protocol/asm/protocol/tx.masm

@@ -9,6 +9,7 @@ use miden::protocol::kernel_proc_offsets::TX_PREPARE_FPI_OFFSET
 use miden::protocol::kernel_proc_offsets::TX_EXEC_FOREIGN_PROC_OFFSET
 use miden::protocol::kernel_proc_offsets::TX_UPDATE_EXPIRATION_BLOCK_DELTA_OFFSET
 use miden::protocol::kernel_proc_offsets::TX_GET_EXPIRATION_DELTA_OFFSET
+use miden::protocol::kernel_proc_offsets::TX_GET_TX_SCRIPT_ROOT_OFFSET
 
 #! Returns the block number of the transaction reference block.
 #!
@@ -319,3 +320,29 @@ pub proc get_expiration_block_delta
     swapdw dropw dropw swapw dropw movdn.3 drop drop drop
     # => [expiration_delta]
 end
+
+#! Returns the transaction script root, or the zero word if no transaction script was executed.
+#!
+#! Inputs:  []
+#! Outputs: [TX_SCRIPT_ROOT]
+#!
+#! Where:
+#! - TX_SCRIPT_ROOT is the root of the transaction script executed in this transaction, or the zero
+#!   word if no transaction script was executed.
+#!
+#! Invocation: exec
+pub proc get_tx_script_root
+    # pad the stack
+    padw padw padw push.0.0.0
+    # => [pad(15)]
+
+    push.TX_GET_TX_SCRIPT_ROOT_OFFSET
+    # => [offset, pad(15)]
+
+    syscall.exec_kernel_proc
+    # => [TX_SCRIPT_ROOT, pad(12)]
+
+    # clean the stack
+    swapdw dropw dropw swapw dropw
+    # => [TX_SCRIPT_ROOT]
+end

crates/miden-testing/src/kernel_tests/tx/test_tx.rs

@@ -752,6 +752,62 @@ async fn test_tx_script_args() -> anyhow::Result<()> {
     Ok(())
 }
 
+/// Tests that `tx::get_tx_script_root` returns the root of the executed transaction script.
+#[tokio::test]
+async fn test_get_script_root_with_script() -> anyhow::Result<()> {
+    let tx_script = CodeBuilder::default().compile_tx_script("begin nop end")?;
+    let expected_root = tx_script.root();
+
+    let code = format!(
+        r#"
+        use miden::protocol::tx
+        use $kernel::prologue
+
+        begin
+            exec.prologue::prepare_transaction
+
+            exec.tx::get_tx_script_root
+            # => [TX_SCRIPT_ROOT]
+
+            push.{expected_root} assert_eqw.err="tx script root mismatch"
+        end
+        "#
+    );
+
+    let tx_context = TransactionContextBuilder::with_existing_mock_account()
+        .tx_script(tx_script)
+        .build()?;
+
+    tx_context.execute_code(&code).await?;
+
+    Ok(())
+}
+
+/// Tests that `tx::get_tx_script_root` returns the zero word when no transaction script is
+/// executed.
+#[tokio::test]
+async fn test_get_script_root_without_script() -> anyhow::Result<()> {
+    let code = r#"
+        use miden::protocol::tx
+        use $kernel::prologue
+
+        begin
+            exec.prologue::prepare_transaction
+
+            exec.tx::get_tx_script_root
+            # => [TX_SCRIPT_ROOT]
+
+            padw assert_eqw.err="tx script root must be zero when no script is executed"
+        end
+        "#;
+
+    let tx_context = TransactionContextBuilder::with_existing_mock_account().build()?;
+
+    tx_context.execute_code(code).await?;
+
+    Ok(())
+}
+
 // Tests that advice map from the account code and transaction script gets correctly passed as
 // part of the transaction advice inputs
 #[tokio::test]