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Data dependency
Feist Josselin edited this page Feb 13, 2019
·
4 revisions
[Work in progress]
Data dependency allows knowing if the value of a given variable is influenced by another variable's value.
Because smart contracts have a state machine based archicture, the results of the data depenency depends of the context (function/contract) of the analysis. Consider the following example:
contract MyContract{
uint a = 0;
uint b = 0;
function setA(uint input_a) public{
a = input_a;
}
function setB() public{
b = a;
}
}
In this example, if we consider only setA
, we have the following dependency:
-
a
is dependent oninput_a
If we consider onlysetB
, we have: -
b
is dependent ona
If we consider the contract entirely (with all the functions), we have: -
a
is dependent oninput_a
-
b
is dependent ona
andinput_a
(by transitivity)
slither.analyses.is_dependent(variable, variable_source, context)
allows to know if variable
is dependent on variable_source
on the given context.
As a result, in our previous example, is_dependent(b, a, funcA)
will return False
, while is_dependent(b, a, myContract)
will return True
:
from slither import Slither
from slither.analyses import is_dependent
slither = Slither('data_dependency_simple_example.sol')
myContract = slither.get_contract_from_name('MyContract')
funcA = myContract.get_function_from_signature('setA(uint256)')
input_a = funcA.parameters[0]
a = myContract.get_state_variable_from_name('a')
b = myContract.get_state_variable_from_name('b')
print(f'{b.name} is dependant from {input_a.name}?: {is_dependent(b, a, funcA)}')
print(f'{b.name} is dependant from {input_a.name}?: {is_dependent(b, a, myContract)}')