From 4d31bc94a6b409849d998872f8a7696ed8fad5b7 Mon Sep 17 00:00:00 2001
From: Michael Vines <mvines@gmail.com>
Date: Tue, 2 Jun 2020 17:34:12 -0700
Subject: [PATCH] Permit builtin programs to be swapped out at epoch boundaries

---
 runtime/src/bank.rs             | 16 +++++++++--
 runtime/src/builtin_programs.rs | 47 ++++++++++++++++++++++++++++-----
 2 files changed, 54 insertions(+), 9 deletions(-)

diff --git a/runtime/src/bank.rs b/runtime/src/bank.rs
index 13c6425f60976e..1b3434a1c05dbe 100644
--- a/runtime/src/bank.rs
+++ b/runtime/src/bank.rs
@@ -10,7 +10,7 @@ use crate::{
     accounts_db::{ErrorCounters, SnapshotStorages},
     accounts_index::Ancestors,
     blockhash_queue::BlockhashQueue,
-    builtin_programs::get_builtin_programs,
+    builtin_programs::{get_builtin_programs, get_epoch_activated_builtin_programs},
     epoch_stakes::{EpochStakes, NodeVoteAccounts},
     message_processor::{MessageProcessor, ProcessInstruction},
     nonce_utils,
@@ -456,6 +456,18 @@ impl Bank {
             {
                 entered_epoch_callback(&mut new)
             }
+
+            if let Some(builtin_programs) =
+                get_epoch_activated_builtin_programs(self.operating_mode(), self.epoch)
+            {
+                for program in builtin_programs.iter() {
+                    self.add_builtin_program(
+                        &program.name,
+                        program.id,
+                        program.process_instruction,
+                    );
+                }
+            }
         }
 
         new.update_epoch_stakes(leader_schedule_epoch);
@@ -2048,7 +2060,7 @@ impl Bank {
     }
 
     pub fn finish_init(&mut self) {
-        let builtin_programs = get_builtin_programs();
+        let builtin_programs = get_builtin_programs(self.operating_mode(), self.epoch);
         for program in builtin_programs.iter() {
             self.add_builtin_program(&program.name, program.id, program.process_instruction);
         }
diff --git a/runtime/src/builtin_programs.rs b/runtime/src/builtin_programs.rs
index 180854990267ce..a5a2fe82764130 100644
--- a/runtime/src/builtin_programs.rs
+++ b/runtime/src/builtin_programs.rs
@@ -1,5 +1,5 @@
 use crate::{message_processor::ProcessInstruction, system_instruction_processor};
-use solana_sdk::{pubkey::Pubkey, system_program};
+use solana_sdk::{clock::Epoch, genesis_config::OperatingMode, pubkey::Pubkey, system_program};
 
 pub struct BuiltinProgram {
     pub name: String,
@@ -16,13 +16,30 @@ impl BuiltinProgram {
     }
 }
 
-pub fn get_builtin_programs() -> Vec<BuiltinProgram> {
+fn new_system_program_activation_epoch(operating_mode: OperatingMode) -> Epoch {
+    match operating_mode {
+        OperatingMode::Development => 0,
+        OperatingMode::Preview => std::u64::MAX / 2,
+        OperatingMode::Stable => std::u64::MAX / 2,
+    }
+}
+
+/// All builtin programs that should be active at the given (operating_mode, epoch)
+pub fn get_builtin_programs(operating_mode: OperatingMode, epoch: Epoch) -> Vec<BuiltinProgram> {
     vec![
-        BuiltinProgram::new(
-            "system_program",
-            system_program::id(),
-            system_instruction_processor::process_instruction,
-        ),
+        if epoch < new_system_program_activation_epoch(operating_mode) {
+            BuiltinProgram::new(
+                "system_program",
+                system_program::id(),
+                system_instruction_processor::process_instruction, // TODO: This is the OLD system instruction processor
+            )
+        } else {
+            BuiltinProgram::new(
+                "system_program",
+                system_program::id(),
+                system_instruction_processor::process_instruction, // TODO: This should be the NEW system instruction processor
+            )
+        },
         BuiltinProgram::new(
             "config_program",
             solana_config_program::id(),
@@ -40,3 +57,19 @@ pub fn get_builtin_programs() -> Vec<BuiltinProgram> {
         ),
     ]
 }
+
+/// Builtin programs that activate at the given (operating_mode, epoch)
+pub fn get_epoch_activated_builtin_programs(
+    operating_mode: OperatingMode,
+    epoch: Epoch,
+) -> Option<Vec<BuiltinProgram>> {
+    if epoch == new_system_program_activation_epoch(operating_mode) {
+        Some(vec![BuiltinProgram::new(
+            "system_program",
+            system_program::id(),
+            system_instruction_processor::process_instruction, // TODO: This should be the NEW system instruction processor
+        )])
+    } else {
+        None
+    }
+}