About ten years ago The firm holding my money put some GM bonds into my investments. The records are gone and now the bonds are called: GENERAL MTRS CO WTS EXP 07/10/20.
If these warrants bought by you on the open market then there's no way to determine your cost basis with no additional information.
If you have a purchase date, you could guesstimate the cost basis by using the price of the warrants that day.
If these warrants arose from the General Motors bankruptcy filing in 2009 (bondholders received warrants). Perhaps they were the Series B $18.33 warrants expiring 7/10/2019 ?
I don't know the answer but there's a calculator at Costbasis.com (Google Costbasis.com)
There was also some discussion on SE at:
Good luck. Answers for such problems require a fair amount of effort to ferret out.