EIP-4200: EOF - Static relative jumps

Author: jangko

nimbus/common/evmforks.nim

@@ -28,3 +28,7 @@ const
   FkParis*          = EVMC_PARIS
   FkShanghai*       = EVMC_SHANGHAI
   FkCancun*         = EVMC_CANCUN
+
+
+  # Meta forks related to specific EIP
+  FkEOF*            = FkCancun

nimbus/evm/code_stream.nim

@@ -64,6 +64,14 @@ proc readVmWord*(c: var CodeStream, n: int): UInt256 =
   for i in 0 ..< toWrite : result_bytes[i] = c.bytes[last - i - 1]
   c.pc = last
 
+proc readInt16*(c: var CodeStream): int =
+  result = (c.bytes[c.pc].int shl 8) or c.bytes[c.pc+1].int
+  c.pc += 2
+
+proc readByte*(c: var CodeStream): byte =
+  result = c.bytes[c.pc]
+  inc c.pc
+
 proc len*(c: CodeStream): int =
   len(c.bytes)
 

nimbus/evm/interpreter/gas_costs.nim

@@ -20,6 +20,7 @@ type
     GasZero,            # Nothing paid for operations of the set Wzero.
     GasBase,            # Amount of gas to pay for operations of the set Wbase.
     GasVeryLow,         # Amount of gas to pay for operations of the set Wverylow.
+    GasMidLow,          # Introduced in Shanghai EIP4200
     GasLow,             # Amount of gas to pay for operations of the set Wlow.
     GasMid,             # Amount of gas to pay for operations of the set Wmid.
     GasHigh,            # Amount of gas to pay for operations of the set Whigh.
@@ -618,9 +619,9 @@ template gasCosts(fork: EVMFork, prefix, ResultGasCostsName: untyped) =
           Msize:          fixed GasBase,
           Gas:            fixed GasBase,
           JumpDest:       fixed GasJumpDest,
-          BeginSub:       fixed GasBase,
-          ReturnSub:      fixed GasLow,
-          JumpSub:        fixed GasHigh,
+          RJump:          fixed GasBase,
+          RJumpI:         fixed GasMidLow,
+          RJumpV:         fixed GasMidLow,
 
           # 5f, 60s & 70s: Push Operations
           Push0:          fixed GasBase,
@@ -720,6 +721,7 @@ const
     GasZero:            0'i64,
     GasBase:            2,
     GasVeryLow:         3,
+    GasMidLow:          4,      # Introduced in Shanghai (EIP4200)
     GasLow:             5,
     GasMid:             8,
     GasHigh:            10,

nimbus/evm/interpreter/op_codes.nim

@@ -126,9 +126,9 @@ type
     JumpDest =       0x5b, ## Mark a valid destination for jumps. This
                            ## operation has no effect on machine state during
                            ## execution.
-    BeginSub =       0x5c, ## Marks the entry point to a subroutine
-    ReturnSub =      0x5d, ## Returns control to the caller of a subroutine.
-    JumpSub =        0x5e, ## Transfers control to a subroutine.
+    Rjump =          0x5c, ## Relative jump (EIP4200)
+    RJumpI =         0x5d, ## Conditional relative jump (EIP4200)
+    RJumpV =         0x5e, ## Relative jump via jump table (EIP4200)
 
     # 5f, 60s & 70s: Push Operations.
     Push0 =          0x5f, ## Place 0 on stack. EIP-3855

nimbus/evm/interpreter/op_handlers/oph_defs.nim

@@ -87,6 +87,11 @@ const
   Vm2OpShanghaiAndLater* =
     Vm2OpParisAndLater - {FkParis}
 
+  Vm2OpCancunAndLater* =
+    Vm2OpShanghaiAndLater - {FkShanghai}
+
+  Vm2OpEOFAndLater* = Vm2OpCancunAndLater
+
 # ------------------------------------------------------------------------------
 # End
 # ------------------------------------------------------------------------------

nimbus/evm/interpreter/op_handlers/oph_memory.nim

@@ -293,6 +293,41 @@ const
     ##       on machine state during execution.
     discard
 
+  # -------
+
+  rjumpOp: Vm2OpFn = proc (k: var Vm2Ctx) =
+    ## 0x5c, Relative jump (EIP4200)
+    let relativeOffset = k.cpt.code.readInt16()
+    k.cpt.code.pc += relativeOffset
+
+  rjumpiOp: Vm2OpFn = proc (k: var Vm2Ctx) =
+    ## 0x5d, Conditional relative jump (EIP4200)
+    let condition = k.cpt.stack.popInt()
+    if condition.isZero:
+      # Not branching, just skip over immediate argument.
+      k.cpt.code.pc += 2
+      return
+
+    k.rjumpOp()
+
+  rjumpvOp: Vm2OpFn = proc (k: var Vm2Ctx) =
+    ## 0x5e, Relative jump via jump table (EIP4200)    
+    let count = k.cpt.code.readByte().int
+    let savedPC = k.cpt.code.pc
+    let idx = k.cpt.stack.popInt().truncate(int)
+    if idx >= count:
+      # Index out-of-bounds, don't branch, just skip over immediate
+      # argument.
+      k.cpt.code.pc += count * 2
+      return
+
+    # get jump table entry
+    k.cpt.code.pc += idx * 2
+    let relativeOffset = k.cpt.code.readInt16()
+
+    # move pc past operand(1 + count * 2) and relativeOffset
+    k.cpt.code.pc = savedPC + count * 2 + relativeOffset
+
 #[
   EIP-2315: temporary disabled
   Reason  : not included in berlin hard fork
@@ -481,6 +516,30 @@ const
      info: "Mark a valid destination for jumps",
      exec: (prep: vm2OpIgnore,
             run:  jumpDestOp,
+            post: vm2OpIgnore)),
+
+    (opCode: RJump,     ## 0x5c, Relative jump (EIP4200)
+     forks: Vm2OpEOFAndLater,
+     name: "RJump",
+     info: "Relative jump via jump table",
+     exec: (prep: vm2OpIgnore,
+            run:  rjumpOp,
+            post: vm2OpIgnore)),
+
+    (opCode: RJumpI,    ## 0x5d, Conditional relative jump (EIP4200)
+     forks: Vm2OpEOFAndLater,
+     name: "RJumpI",
+     info: "Relative jump via jump table",
+     exec: (prep: vm2OpIgnore,
+            run:  rjumpiOp,
+            post: vm2OpIgnore)),
+
+    (opCode: RJumpV,    ## 0x5e, Relative jump via jump table (EIP4200)
+     forks: Vm2OpEOFAndLater,
+     name: "RJumpV",
+     info: "Relative jump via jump table",
+     exec: (prep: vm2OpIgnore,
+            run:  rjumpvOp,
             post: vm2OpIgnore))]
 
 #[