Subroutines (ethereum#2503)

* Update eip-615.md

* Update eip-615.md

* Update eip-615.md

MD here is not MD there is junk everywhere.

* Update eip-615.md

* Update eip-615.md

* Add security issue caught by @holiman

* Reconcile opcodes and names with eip-615

* nudge

* email

EIPS/eip-2315.md

@@ -4,14 +4,14 @@ title: Simple Subroutines for the EVM
 status: Draft
 type: Standards Track
 category: Core
-author: Greg Colvin
+author: Greg Colvin ([email protected])
 discussions-to: https://ethereum-magicians.org/t/eip-2315-simple-subroutines-for-the-evm/3941
 created: 2019-10-17
 ---
 
 ## Abstract
 
-This proposal introduces two opcodes to support subroutines:  `JUMPSUB` and `RETSUB`.
+This proposal introduces two opcodes to support subroutines:  `JUMPSUB` and `RETURNSUB`.
 
 ## Motivation
 
@@ -22,10 +22,10 @@ The EVM does not provide subroutines as a primitive.  Instead, calls must be syn
 ##### `JUMPSUB`
 Jumps to the address on top of the stack, which must be the offset of a `JUMPDEST`.
 
-##### `RETSUB`
-Returns to the instruction after the most recently executed `JUMPSUB` instruction.
+##### `RETURNSUB`
+Returns to the most recently executed `JUMPSUB` and executes the following instruction.
 
-A program may `JUMPSUB` at most 1023 times without an intervening `RETSUB`.
+A program may `JUMPSUB` at most 1023 times without an intervening `RETURNSUB`.  A program which executes `RETURNSUB` without no prior `BEGINSUB` will `STOP`.
 
 ## Rationale
 
@@ -38,19 +38,19 @@ These changes do not affect the semantics of existing EVM code.
 ## Test Cases
 ```
 step op       stack
-0    PUSH1 3  []
-1    JUMPSUB  [3]
-4    STOP     []
-2    JUMPDEST []
-3    RETSUB   []
+0    PUSH1 3   []
+1    JUMPSUB   [3]
+4    STOP      []
+2    JUMPDEST  []
+3    RETURNSUB []
 ```
-This code should terminate after 5 steps with an empty stack.
+This code should terminate after 4 steps with an empty stack.
 
 ## Implementations
 
 No clients have implemented this proposal as of yet.
 
-The new operators proposed here are implemented by the following pseudocode, which adds cases for `JUMPSUB` and `RETSUB` to a simple loop-and-switch interpreter.
+The new operators proposed here are implemented by the following pseudocode, which adds cases for `JUMPSUB` and `RETURNSUB` to a simple loop-and-switch interpreter.
 ```
 bytecode[code_size]
 data_stack[1024]
@@ -65,22 +65,25 @@ loop: while PC < code_size {
       push(return_stack, PC)
       PC = pop(data_stack)
       continue loop
-   case RETSUB:
+   case RETURNSUB:
       PC = pop(return_stack)
    }
    ++PC
 }
 ```
-Execution of EVM bytecode begins with one value on the return stack—the size of the bytecode. The virtual byte of 0 at this offset is the EVM `STOP` opcode, so executing a `RETSUB` with no prior `JUMPSUB` executes a `STOP`.  A `STOP` or `RETURN` ends the execution of the subroutine and the program.
+Execution of EVM bytecode begins with one value on the return stack—the size of the bytecode. The virtual byte of 0 at this offset is the EVM `STOP` opcode, so executing a `RETURNSUB` with no prior `JUMPSUB` executes a `STOP`.  A `STOP` or `RETURN` ends the execution of the subroutine and the program.
 
-We suggest the cost of `JUMPSUB` should be _low_, and `RETSUB` should be _verylow_. 
+### Costs and Codes
+
+We suggest the cost of `JUMPSUB` should be _low_, and `RETURNSUB` should be _verylow_. 
  Measurement will tell.  We suggest the following opcodes:
 ```
-0xbe JUMPSUB
-0xbf RETSUB
+0xb3 JUMPSUB
+0xb7 RETURNSUB
 ```
 ## Security Considerations
 
-Program flow analysis frameworks will need to be updated to allow for a new type of branch -`JUMPSUB` - and new type of branching, since a `RETSUB` will cause a jump to a destination which is not a `JUMPDEST`. 
+Program flow analysis frameworks will need to be updated to allow for a new type of branch -`JUMPSUB` - and new type of branching - `RETURNSUB` will cause a jump to a destination which is 
+a `JUMPSUB`, not a `JUMPDEST`. 
 
 **Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).**