fix!: Remove EVM emulator gas stipend (#82)

# What ❔

Removes the EVM emulator gas stipend and replaces it with a memory
stipend.

## Why ❔

Aligns with the changes in the legacy VM.

Author: slowli

crates/vm2-interface/src/state_interface.rs

@@ -115,8 +115,6 @@ pub trait CallframeInterface {
     fn gas(&self) -> u32;
     /// Sets the remaining amount of gas.
     fn set_gas(&mut self, new_gas: u32);
-    /// Additional gas provided for the duration of this callframe.
-    fn stipend(&self) -> u32;
 
     /// Returns the context value for this call. This context is accessible via [`ContextU128`](crate::opcodes::ContextU128) opcode.
     fn context_u128(&self) -> u128;
@@ -379,10 +377,6 @@ pub(crate) mod testonly {
             unimplemented!()
         }
 
-        fn stipend(&self) -> u32 {
-            unimplemented!()
-        }
-
         fn context_u128(&self) -> u128 {
             unimplemented!()
         }

crates/vm2/src/callframe.rs

@@ -13,6 +13,9 @@ use crate::{
     Instruction, World,
 };
 
+// FIXME: use `zkevm_opcode_defs::system_params` once it's released
+const NEW_EVM_FRAME_MEMORY_STIPEND: u32 = 56 << 10;
+
 #[derive(Debug)]
 pub(crate) struct Callframe<T, W> {
     pub(crate) address: H160,
@@ -25,7 +28,6 @@ pub(crate) struct Callframe<T, W> {
     pub(crate) stack: Box<Stack>,
     pub(crate) sp: u16,
     pub(crate) gas: u32,
-    pub(crate) stipend: u32,
     pub(crate) near_calls: Vec<NearCallFrame>,
     pub(crate) pc: *const Instruction<T, W>,
     pub(crate) program: Program<T, W>,
@@ -68,15 +70,17 @@ impl<T, W> Callframe<T, W> {
         aux_heap: HeapId,
         calldata_heap: HeapId,
         gas: u32,
-        stipend: u32,
         exception_handler: u16,
         context_u128: u128,
         is_static: bool,
+        is_evm_interpreter: bool,
         world_before_this_frame: Snapshot,
     ) -> Self {
         let is_kernel = is_kernel(address);
         let heap_size = if is_kernel {
             NEW_KERNEL_FRAME_MEMORY_STIPEND
+        } else if is_evm_interpreter {
+            NEW_EVM_FRAME_MEMORY_STIPEND
         } else {
             NEW_FRAME_MEMORY_STIPEND
         };
@@ -99,7 +103,6 @@ impl<T, W> Callframe<T, W> {
             heaps_i_am_keeping_alive: vec![],
             sp: 0,
             gas,
-            stipend,
             exception_handler,
             near_calls: vec![],
             world_before_this_frame,
@@ -253,7 +256,6 @@ impl<T, W> Clone for Callframe<T, W> {
             stack: self.stack.clone(),
             sp: self.sp,
             gas: self.gas,
-            stipend: self.stipend,
             near_calls: self.near_calls.clone(),
             pc: self.pc,
             program: self.program.clone(),
@@ -279,7 +281,6 @@ impl<T, W> PartialEq for Callframe<T, W> {
             && self.stack == other.stack
             && self.sp == other.sp
             && self.gas == other.gas
-            && self.stipend == other.stipend
             && self.near_calls == other.near_calls
             && self.pc == other.pc
             && self.program == other.program

crates/vm2/src/instruction_handlers/far_call.rs

@@ -1,8 +1,5 @@
 use primitive_types::U256;
-use zkevm_opcode_defs::{
-    system_params::{EVM_SIMULATOR_STIPEND, MSG_VALUE_SIMULATOR_ADDITIVE_COST},
-    ADDRESS_MSG_VALUE,
-};
+use zkevm_opcode_defs::{system_params::MSG_VALUE_SIMULATOR_ADDITIVE_COST, ADDRESS_MSG_VALUE};
 use zksync_vm2_interface::{
     opcodes::{FarCall, TypeLevelCallingMode},
     Tracer,
@@ -62,7 +59,7 @@ where
                 0
             };
 
-        let failing_part = (|| {
+        let fallible_part = (|| {
             let decommit_result = vm.world_diff.decommit(
                 world,
                 tracer,
@@ -108,25 +105,16 @@ where
 
         // A far call pushes a new frame and returns from it in the next instruction if it panics.
         let (calldata, program, is_evm_interpreter) =
-            failing_part.unwrap_or_else(|| (U256::zero().into(), Program::new_panicking(), false));
-
-        let stipend = if is_evm_interpreter {
-            EVM_SIMULATOR_STIPEND
-        } else {
-            0
-        };
-        let new_frame_gas = new_frame_gas
-            .checked_add(stipend)
-            .expect("stipend must not cause overflow");
+            fallible_part.unwrap_or_else(|| (U256::zero().into(), Program::new_panicking(), false));
 
         let new_frame_is_static = IS_STATIC || vm.state.current_frame.is_static;
         vm.push_frame::<M>(
             u256_into_address(destination_address),
             program,
             new_frame_gas,
-            stipend,
             exception_handler,
             new_frame_is_static && !is_evm_interpreter,
+            is_evm_interpreter,
             calldata.memory_page,
             vm.world_diff.snapshot(),
         );

crates/vm2/src/instruction_handlers/ret.rs

@@ -55,11 +55,7 @@ fn naked_ret<T: Tracer, W: World<T>, RT: TypeLevelReturnType, const TO_LABEL: bo
             result
         };
 
-        let leftover_gas = vm
-            .state
-            .current_frame
-            .gas
-            .saturating_sub(vm.state.current_frame.stipend);
+        let leftover_gas = vm.state.current_frame.gas;
 
         let Some(FrameRemnant {
             exception_handler,

crates/vm2/src/single_instruction_test/callframe.rs

@@ -1,6 +1,5 @@
 use arbitrary::Arbitrary;
 use primitive_types::H160;
-use zkevm_opcode_defs::EVM_SIMULATOR_STIPEND;
 use zksync_vm2_interface::{HeapId, Tracer};
 
 use super::stack::{Stack, StackPool};
@@ -40,9 +39,7 @@ impl<'a, T: Tracer, W: World<T>> Arbitrary<'a> for Callframe<T, W> {
             is_kernel: is_kernel(address),
             stack: Box::new(Stack::new_arbitrary(u, calldata_heap, base_page)?),
             sp: u.arbitrary()?,
-            // It is assumed that it is always possible to add the stipend
-            gas: u.int_in_range(0..=u32::MAX - EVM_SIMULATOR_STIPEND)?,
-            stipend: u.arbitrary()?,
+            gas: u.arbitrary()?,
             near_calls: vec![],
             pc: program.instruction(0).unwrap(),
             program,
@@ -78,7 +75,6 @@ impl<T: Tracer, W: World<T>> Callframe<T, W> {
             stack: StackPool {}.get(),
             sp: 0,
             gas: 0,
-            stipend: 0,
             near_calls: vec![],
             pc: std::ptr::null(),
             program: Program::for_decommit(),

crates/vm2/src/single_instruction_test/state_to_zk_evm.rs

@@ -86,7 +86,7 @@ fn vm2_frame_to_zk_evm_frames<T, W>(
         heap_bound: frame.heap_size,
         aux_heap_bound: frame.aux_heap_size,
         total_pubdata_spent: PubdataCost(0),
-        stipend: frame.stipend,
+        stipend: 0,
     };
 
     let mut result = vec![far_frame];

crates/vm2/src/state.rs

@@ -63,7 +63,7 @@ impl<T, W> State<T, W> {
                 gas,
                 0,
                 0,
-                0,
+                false,
                 false,
                 world_before_this_frame,
             ),

crates/vm2/src/tests/mod.rs

@@ -3,5 +3,4 @@
 mod bytecode_behaviour;
 mod far_call_decommitment;
 mod panic;
-mod stipend;
 mod trace_failing_far_call;

crates/vm2/src/tests/stipend.rs

@@ -194,10 +194,6 @@ impl<T: Tracer, W: World<T>> CallframeInterface for CallframeWrapper<'_, T, W> {
         self.frame.is_kernel
     }
 
-    fn stipend(&self) -> u32 {
-        self.frame.stipend
-    }
-
     fn context_u128(&self) -> u128 {
         self.frame.context_u128
     }
@@ -472,9 +468,9 @@ mod test {
                 H160::from_low_u64_be(1),
                 program.clone(),
                 (*counter).into(),
-                0,
                 *counter,
                 false,
+                false,
                 HeapId::from_u32_unchecked(5),
                 vm.world_diff.snapshot(),
             );