Have chronic lymphocytic leukemia or small lymphocytic lymphoma that requires treatment

Have received prior treatment, including with a type of medicine called a BTK inhibitor

Be well enough to perform their own personal care

Have adequate organ function and blood counts, as measured by blood tests

Have cancer that has become very aggressive or has spread to the brain or spinal cord

Have serious heart disease

Need a blood thinner called warfarin

Have any problems absorbing food or medicine taken by mouth

Take certain medicines that affect how fast the study drug is broken down in the body

Have active infection