Update EIP-663: Replace runtime stack checks with EOF validation rules (

ethereum#7241)

EIPS/eip-663.md

@@ -8,7 +8,7 @@ status: Review
 type: Standards Track
 category: Core
 created: 2017-07-03
-requires: 3540
+requires: 3540, 5450
 ---
 
 ## Abstract
@@ -34,22 +34,19 @@ We introduce two new instructions:
 
 If the code is legacy bytecode, both of these instructions result in an *exceptional halt*. (*Note: This means no change to behaviour.*)
 
-If the code is valid EOF1, the following execution rules apply:
+If the code is valid EOF1, the following rules apply:
 
  1. These instructions are followed by an 8-bit immediate value, which we call `imm`, and can have a value of 0 to 255. We introduce the variable `n` which equals to `imm + 1`.
 
- 2. For `DUPN`:
+ 2. Code validation is extended to check that no relative jump instruction (`RJUMP`/`RJUMPI`/`RJUMPV`) targets immmediate values of `DUPN` or `SWAPN`.
 
-   - If the current stack height is less than `n`, then a stack underflow exception is issued.
-   - If the current stack height is at the limit (1024), a stack overflow exception is issued.
-   - Otherwise the `n`'th stack item is duplicated at the top of the stack. (*Note: We use 1-based indexing here.*)
+ 3. The stack validation algorithm of [EIP-5450](./eip-5450.md) is extended:
+  3.1. Before `DUPN` if the current stack height is less than `n`, code is invalid. After `DUPN` stack height is incremented.
+  3.2. Before `SWAPN` if the current stack height is less than `n + 1`, code is invalid. After `SWAPN` stack height is not changed.
 
- 3. For `SWAPN`:
-
-   - If the current stack height is less than `n + 1`, then a stack underflow exception is issued.
-   - Otherwise the `n + 1`th stack item is swapped with the top stack item.
-
-Clarification: the "stack underflow/overflow exception" means the EVM execution is halted and all gas is consumed.
+ 4. Execution rules:
+  4.1. `DUPN`: the `n`'th stack item is duplicated at the top of the stack. (*Note: We use 1-based indexing here.*)
+  4.2  `SWAPN`: the `n + 1`th stack item is swapped with the top stack item.
 
 The gas cost for both instructions is set at 3.
 
@@ -72,13 +69,13 @@ This has no effect on backwards compatibility because the opcodes were not previ
 
 ## Test Cases
 
-For `0 <= n <= 255`:
+Given variable `n`, which equals to `imm + 1`, for `1 <= n <= 256`:
 
-    - `DUPN n` to fail if `stack_height < n`.
-    - `SWAPN n` to fail if `stack_height < (n + 1)`.
-    - `DUPN n` to fail if `stack_height + 1 > 1024`.
-    - `DUPN n` and `SWAPN n` to fail if gas available is less than 3.
-    - otherwise `DUPN n` should push the `stack[n]` item to the stack, and `SWAPN n` should swap `stack[n + 1]` with `stack[stack.top()]`.
+    - `DUPN imm` to fail validation if `stack_height < n`.
+    - `SWAPN imm` to fail validation if `stack_height < (n + 1)`.
+    - `DUPN imm` to increment maximum stack height of a function. Validation fails if maximum stack height exceeds limit of 1023.
+    - `DUPN imm` and `SWAPN imm` to fail at run-time if gas available is less than 3.
+    - otherwise `DUPN imm` should push the `stack[n]` item to the stack, and `SWAPN imm` should swap `stack[n + 1]` with `stack[stack.top()]`.
 
 ## Security Considerations