CSR expenses debited in profit and loss account are considered as non business expense under the law hence disallowed in computing business income.
Whether such expenditure could be claimed from gross total income the law however does not expressly so prohibit such course.
In the Voltas case reported at  19 ITR-OL 739 (Bom) the company successfully managed to get deduction of disallowed CSR expenditure u/s 80G in an assessment completed u/s 143(3). This was the first year of section 37(1) explanation 2 application test.
The revenue challenged this method of claim in reassessment proceedings but failed because of faulty approval u/s 151.
In a way therefore the original assessment u/s 143(3) survived leaving a good benchmark for claim of CSR expenses from the gross total income.