Beedle - Oracle free perpetual lending

Summary

When fetching data from a storage location, assigning the data to a memory variable causes all fields of the struct/array to be read from storage, which incurs a Gcoldsload (2,100 gas) for each field of the struct/array. If the fields are read from the new memory variable, they incur an additional MLOAD rather than a cheap stack read. Instead of declaring the variable with the memory keyword, declaring the variable with the storage keyword and caching any fields that need to be re-read in stack variables, will be much cheaper, only incurring the Gcoldsload for the fields actually read. The only time it makes sense to read the whole struct/array into a memory variable is if the full struct/array is being returned by the function, is being passed to a function that requires memory, or if the array/struct is being read from another memory array/struct.

Vulnerability Details

There are 10 instances of this issue.

Impact

42,000 gas

Tools Used

baudit: a custom static code analysis tool; manual review

Recommendations

Use storage instead of memory for structs and arrays.