From 7c9436a6f24cdb01f776e0d888bb40b6ab7ea92e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alexander=20Mei=C3=9Fner?= <AlexanderMeissner@gmx.net>
Date: Tue, 16 Aug 2022 11:14:09 +0200
Subject: [PATCH] Removes TransactionContext::get_instruction_trace(). Adds
 TransactionContext::get_instruction_trace_length() and
 TransactionContext::get_instruction_context_at_index().

---
 programs/bpf_loader/src/syscalls/mod.rs | 29 ++++++++++++++++---------
 runtime/src/message_processor.rs        |  2 +-
 sdk/src/transaction_context.rs          | 25 +++++++++++++--------
 3 files changed, 36 insertions(+), 20 deletions(-)

diff --git a/programs/bpf_loader/src/syscalls/mod.rs b/programs/bpf_loader/src/syscalls/mod.rs
index 0ef173d63dfa6b..2893849a9f0582 100644
--- a/programs/bpf_loader/src/syscalls/mod.rs
+++ b/programs/bpf_loader/src/syscalls/mod.rs
@@ -1712,25 +1712,34 @@ declare_syscall!(
         // Reverse iterate through the instruction trace,
         // ignoring anything except instructions on the same level
         let stack_height = invoke_context.get_stack_height();
-        let instruction_trace = invoke_context.transaction_context.get_instruction_trace();
-        let mut current_index = 0;
-        let mut instruction_context = None;
-        for current_instruction_context in instruction_trace.iter().rev() {
-            if current_instruction_context.get_stack_height() == TRANSACTION_LEVEL_STACK_HEIGHT
+        let instruction_trace_length = invoke_context
+            .transaction_context
+            .get_instruction_trace_length();
+        let mut reverse_index_at_stack_height = 0;
+        let mut found_instruction_context = None;
+        for index_in_trace in (0..instruction_trace_length).rev() {
+            let instruction_context = question_mark!(
+                invoke_context
+                    .transaction_context
+                    .get_instruction_context_at_index_in_trace(index_in_trace)
+                    .map_err(SyscallError::InstructionError),
+                result
+            );
+            if instruction_context.get_stack_height() == TRANSACTION_LEVEL_STACK_HEIGHT
                 && stack_height > TRANSACTION_LEVEL_STACK_HEIGHT
             {
                 break;
             }
-            if current_instruction_context.get_stack_height() == stack_height {
-                if index.saturating_add(1) == current_index {
-                    instruction_context = Some(current_instruction_context);
+            if instruction_context.get_stack_height() == stack_height {
+                if index.saturating_add(1) == reverse_index_at_stack_height {
+                    found_instruction_context = Some(instruction_context);
                     break;
                 }
-                current_index = current_index.saturating_add(1);
+                reverse_index_at_stack_height = reverse_index_at_stack_height.saturating_add(1);
             }
         }
 
-        if let Some(instruction_context) = instruction_context {
+        if let Some(instruction_context) = found_instruction_context {
             let ProcessedSiblingInstruction {
                 data_len,
                 accounts_len,
diff --git a/runtime/src/message_processor.rs b/runtime/src/message_processor.rs
index 23eb1e800e9818..c95bfc0b72eae2 100644
--- a/runtime/src/message_processor.rs
+++ b/runtime/src/message_processor.rs
@@ -680,6 +680,6 @@ mod tests {
                 InstructionError::Custom(0xbabb1e)
             ))
         );
-        assert_eq!(transaction_context.get_instruction_trace().len(), 2);
+        assert_eq!(transaction_context.get_instruction_trace_length(), 2);
     }
 }
diff --git a/sdk/src/transaction_context.rs b/sdk/src/transaction_context.rs
index ca5cba14db312a..a90755ca16ac61 100644
--- a/sdk/src/transaction_context.rs
+++ b/sdk/src/transaction_context.rs
@@ -137,6 +137,21 @@ impl TransactionContext {
         self.account_keys.iter().rposition(|key| key == pubkey)
     }
 
+    /// Returns instruction trace length
+    pub fn get_instruction_trace_length(&self) -> usize {
+        self.instruction_trace.len()
+    }
+
+    /// Gets an InstructionContext by its index in the trace
+    pub fn get_instruction_context_at_index_in_trace(
+        &self,
+        index_in_trace: usize,
+    ) -> Result<&InstructionContext, InstructionError> {
+        self.instruction_trace
+            .get(index_in_trace)
+            .ok_or(InstructionError::CallDepth)
+    }
+
     /// Gets an InstructionContext by its nesting level in the stack
     pub fn get_instruction_context_at_nesting_level(
         &self,
@@ -146,10 +161,7 @@ impl TransactionContext {
             .instruction_stack
             .get(nesting_level)
             .ok_or(InstructionError::CallDepth)?;
-        let instruction_context = self
-            .instruction_trace
-            .get(index_in_trace)
-            .ok_or(InstructionError::CallDepth)?;
+        let instruction_context = self.get_instruction_context_at_index_in_trace(index_in_trace)?;
         debug_assert_eq!(instruction_context.nesting_level, nesting_level);
         Ok(instruction_context)
     }
@@ -265,11 +277,6 @@ impl TransactionContext {
         Ok(())
     }
 
-    /// Returns instruction trace
-    pub fn get_instruction_trace(&self) -> &[InstructionContext] {
-        &self.instruction_trace
-    }
-
     /// Calculates the sum of all lamports within an instruction
     fn instruction_accounts_lamport_sum(
         &self,