Add return data implementation

This consists of:
 - syscalls
 - passing return data from invoked to invoker
 - printing to stable log
 - rust and C SDK changes

programs/bpf/rust/invoke/src/lib.rs

@@ -10,7 +10,7 @@ use solana_program::{
     entrypoint,
     entrypoint::{ProgramResult, MAX_PERMITTED_DATA_INCREASE},
     msg,
-    program::{invoke, invoke_signed},
+    program::{get_return_data, invoke, invoke_signed, set_return_data},
     program_error::ProgramError,
     pubkey::{Pubkey, PubkeyError},
     system_instruction,
@@ -394,6 +394,27 @@ fn process_instruction(
                     assert_eq!(data[i], i as u8);
                 }
             }
+
+            msg!("Test return data via invoked");
+            {
+                // this should be cleared on entry, the invoked tests for this
+                set_return_data(b"x");
+
+                let instruction = create_instruction(
+                    *accounts[INVOKED_PROGRAM_INDEX].key,
+                    &[(accounts[ARGUMENT_INDEX].key, false, true)],
+                    vec![SET_RETURN_DATA],
+                );
+                let _ = invoke(&instruction, accounts);
+
+                assert_eq!(
+                    get_return_data(),
+                    Some((
+                        *accounts[INVOKED_PROGRAM_INDEX].key,
+                        b"Set by invoked".to_vec()
+                    ))
+                );
+            }
         }
         TEST_PRIVILEGE_ESCALATION_SIGNER => {
             msg!("Test privilege escalation signer");