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.
@@ -712,6 +713,11 @@ template gasCosts(fork: EVMFork, prefix, ResultGasCostsName: untyped) =
           Log3:           memExpansion `prefix gasLog3`,
           Log4:           memExpansion `prefix gasLog4`,
 
+          # e0s: Static jumps
+          RJump:          fixed GasBase,
+          RJumpI:         fixed GasMidLow,
+          RJumpV:         fixed GasMidLow,
+
           # f0s: System operations
           Create:         complex `prefix gasCreate`,
           Call:           complex `prefix gasCall`,
@@ -732,6 +738,7 @@ 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

@@ -127,6 +127,7 @@ type
     JumpDest =       0x5b, ## Mark a valid destination for jumps. This
                            ## operation has no effect on machine state during
                            ## execution.
+
     Tload =          0x5c, ## Load word from transient storage.
     Tstore =         0x5d, ## Save word to transient storage.
 
@@ -182,8 +183,13 @@ type
     Nop0xC9, Nop0xCA, Nop0xCB, Nop0xCC, Nop0xCD, Nop0xCE,
     Nop0xCF, Nop0xD0, Nop0xD1, Nop0xD2, Nop0xD3, Nop0xD4,
     Nop0xD5, Nop0xD6, Nop0xD7, Nop0xD8, Nop0xD9, Nop0xDA,
-    Nop0xDB, Nop0xDC, Nop0xDD, Nop0xDE, Nop0xDF, Nop0xE0,
-    Nop0xE1, Nop0xE2, Nop0xE3, Nop0xE4, Nop0xE5, Nop0xE6,
+    Nop0xDB, Nop0xDC, Nop0xDD, Nop0xDE, Nop0xDF,
+
+    Rjump =          0xe0, ## Relative jump (EIP4200)
+    RJumpI =         0xe1, ## Conditional relative jump (EIP4200)
+    RJumpV =         0xe2, ## Relative jump via jump table (EIP4200)
+
+    Nop0xE3, Nop0xE4, Nop0xE5, Nop0xE6,
     Nop0xE7, Nop0xE8, Nop0xE9, Nop0xEA, Nop0xEB, Nop0xEC,
     Nop0xED, Nop0xEE, Nop0xEF, ## ..
 

nimbus/evm/interpreter/op_handlers/oph_defs.nim

@@ -89,6 +89,8 @@ const
   Vm2OpCancunAndLater* =
     Vm2OpShanghaiAndLater - {FkShanghai}
 
+  Vm2OpEOFAndLater* = Vm2OpCancunAndLater
+
 # ------------------------------------------------------------------------------
 # End
 # ------------------------------------------------------------------------------

nimbus/evm/interpreter/op_handlers/oph_memory.nim

@@ -334,6 +334,39 @@ const
 
     k.cpt.memory.copy(dstPos, srcPos, len)
 
+  rjumpOp: Vm2OpFn = proc (k: var Vm2Ctx) =
+    ## 0xe0, Relative jump (EIP4200)
+    let relativeOffset = k.cpt.code.readInt16()
+    k.cpt.code.pc += relativeOffset
+
+  rjumpiOp: Vm2OpFn = proc (k: var Vm2Ctx) =
+    ## 0xe1, 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) =
+    ## 0xe2, 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
@@ -546,6 +579,30 @@ const
      info: "Copy memory",
      exec: (prep: vm2OpIgnore,
             run:  mCopyOp,
+            post: vm2OpIgnore)),
+
+    (opCode: RJump,     ## 0xe0, Relative jump (EIP4200)
+     forks: Vm2OpEOFAndLater,
+     name: "RJump",
+     info: "Relative jump via jump table",
+     exec: (prep: vm2OpIgnore,
+            run:  rjumpOp,
+            post: vm2OpIgnore)),
+
+    (opCode: RJumpI,    ## 0xe1, Conditional relative jump (EIP4200)
+     forks: Vm2OpEOFAndLater,
+     name: "RJumpI",
+     info: "Relative jump via jump table",
+     exec: (prep: vm2OpIgnore,
+            run:  rjumpiOp,
+            post: vm2OpIgnore)),
+
+    (opCode: RJumpV,    ## 0xe2, Relative jump via jump table (EIP4200)
+     forks: Vm2OpEOFAndLater,
+     name: "RJumpV",
+     info: "Relative jump via jump table",
+     exec: (prep: vm2OpIgnore,
+            run:  rjumpvOp,
             post: vm2OpIgnore))]
 
 #[