I would use a product specifically designed for repairing cracks in concrete, something like:
Carefully follow all the instructions that come with the product, plus:
Thorough cleaning and preparation of the cracks is vital when using "crack repair" products. If you take shortcuts on the prep-work, the repair (patch) will never look that good, and will more than likely "fail" fairly quickly.
Personally, while I was doing the prep-work on the cracks, I would also take the time to prepare the complete concrete porch roof for repainting.
Then to finish the job properly, once you've repaired the cracks, waited at least a further 24 hours:
- Clean "lightly" the complete concrete porch roof (you previously cleaned it properly while preparing the cracks).
- Repaint the complete concrete porch roof with a suitable exterior grade paint.