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Feist Josselin edited this page Oct 18, 2018 · 13 revisions

SlithIR

Slither possesses an intermediate representation, called SlithIR.

SlithIR allows:

  • To simplify code analysis
  • To write more precise detectors
  • To support taint and value tracking

SlihtIR is an ongoing project, contact us for more information.

Example

$ slither file.sol --printer-slithir will output the IR for every function.

$ slither examples/printers/slihtir.sol --printer-slithir
Contract UnsafeMath
	Function add(uint256,uint256)
		Expression: a + b
		IRs:
			TMP_0(uint256) = a + b
			RETURN TMP_0
	Function min(uint256,uint256)
		Expression: a - b
		IRs:
			TMP_0(uint256) = a - b
			RETURN TMP_0
Contract MyContract
	Function transfer(address,uint256)
		Expression: balances[msg.sender] = balances[msg.sender].min(val)
		IRs:
			REF_3(uint256) -> balances[msg.sender]
			REF_1(uint256) -> balances[msg.sender]
			TMP_1(uint256) = LIBRARY_CALL, dest:UnsafeMath, function:min, arguments:['REF_1', 'val'] 
			REF_3 := TMP_1
		Expression: balances[to] = balances[to].add(val)
		IRs:
			REF_3(uint256) -> balances[to]
			REF_1(uint256) -> balances[to]
			TMP_1(uint256) = LIBRARY_CALL, dest:UnsafeMath, function:add, arguments:['REF_1', 'val'] 
			REF_3 := TMP_1

SlithIR Specification

Variables

  • StateVariable
  • LocalVariable
  • Constant (string or int)
  • SolidityVariable
  • TupleVariable
  • TemporaryVariable (variables added by slithIR)
  • ReferenceVariable (variables added by slithIR, for mapping/index accesses)

In the following we use:

  • a LVALUE can be: StateVariable, LocalVariable, TemporaryVariable, ReferenceVariable or TupleVariable

  • a RVALUE can be: StateVariable, LocalVariable, Constant, SolidityVariable, TemporaryVariable or ReferenceVariable

Operators

Assignment

  • LVALUE := RVALUE
  • LVALUE := Tuple
  • LVALUE := Function (for dynamic function)

Binary Operation

  • LVALUE = RVALUE ** RVALUE
  • LVALUE = RVALUE * RVALUE
  • LVALUE = RVALUE / RVALUE
  • LVALUE = RVALUE % RVALUE
  • LVALUE = RVALUE + RVALUE
  • LVALUE = RVALUE - RVALUE
  • LVALUE = RVALUE << RVALUE
  • LVALUE = RVALUE >> RVALUE
  • LVALUE = RVALUE & RVALUE
  • LVALUE = RVALUE ^ RVALUE
  • LVALUE = RVALUE | RVALUE
  • LVALUE = RVALUE < RVALUE
  • LVALUE = RVALUE > RVALUE
  • LVALUE = RVALUE <= RVALUE
  • LVALUE = RVALUE >= RVALUE
  • LVALUE = RVALUE == RVALUE
  • LVALUE = RVALUE != RVALUE
  • LVALUE = RVALUE && RVALUE
  • LVALUE = RVALUE -- RVALUE

Unary Operation

  • LVALUE = ! RVALUE
  • LVALUE = ~ RVALUE

Index

  • REFERENCE -> LVALUE [ RVALUE ]

Note: The reference points to the memory location

Member

  • REFERENCE -> LVALUE . RVALUE
  • REFERENCE -> CONTRACT . RVALUE
  • REFERENCE -> ENUM . RVALUE

Note: The reference points to the memory location

New Operators

  • LVALUE = NEW_ARRAY ARRAY_TYPE DEPTH(:int)

ARRAY_TYPE is a solidity_types

DEPTH is used for arrays of multi-dimension)

  • LVALUE = NEW_CONTRACT CONSTANT
  • LVALUE = NEW_STRUCTURE STRUCTURE
  • LVALUE = NEW_ELEMENTARY_TYPE ELEMENTARY_TYPE

ELEMENTARY_TYPE is defined in slither/core/solidity_types/elementary_type.py

Push Operator

  • PUSH LVALUE RVALUE

Delete Operator

  • DELETE LVALUE

Conversion

  • CONVERT LVALUE RVALUE TYPE

TYPE is a solidity_types

Unpack

  • LVALUE = UNPACK TUPLEVARIABLE INDEX(:int)

Array Initialization

  • LVALUE = INIT_VALUES

INIT_VALUES is a list of RVALUE, or a list of list in case of a multi dimensions array.

Calls Operators

In the following, ARG is a variable as defined in SlithIR#variables

  • LVALUE = HIGH_LEVEL_CALL DESTINATION FUNCTION [ARG, ..]
  • LVALUE = LOW_LEVEL_CALL DESTINATION FUNCTION_NAME [ARG, ..]

FUNCTION_NAME can only be call/delegatecall/codecall

  • LVALUE = SOLIDITY_CALL SOLIDITY_FUNCTION [ARG, ..]

SOLIDITY_FUNCTION is defined in slither/core/declarations/solidity_variables.py

  • LVALUE = INTERNAL_CALL FUNCTION [ARG, ..]
  • LVALUE = INTERNAL_DYNAMIC_CALL FUNCTION_TYPE [ARG, ..]

INTERNAL_DYNAMIC_CALL represent pointer of function.

FUNCTION_TYPE is defined in slither/core/solidity_types/function_type.py

  • LVALUE = LIBRARY_CALL DESTINATION FUNCTION_NAME [ARG, ..]
  • LVALUE = EVENT_CALL EVENT_NAME [ARG, ..]
  • LVALUE = SEND DESTINATION VALUE
  • TRANSFER DESTINATION VALUE

Optional arguments:

  • GAS and VALUE for HIGH_LEVEL_CALL / LOW_LEVEL_CALL.

Return

  • RETURN RVALUE
  • RETURN TUPLE
  • RETURN None

Return None represents an empty return statement

Condition

  • CONDITION RVALUE

CONDITION holds the condition in a conditional node.

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