Function sol_get_return_data 

pub unsafe fn sol_get_return_data(
    data: *mut u8,
    length: u64,
    program_id: *mut u8,
) -> u64

Read CPI return data set by the most recent CPI.

Returns the runtime-reported data length. If the return data is larger than the provided buffer, only length bytes are copied into data.

Safety

data must be valid for length writable bytes and program_id must point to 32 writable bytes.