I'm still studying OS concepts and trying to understand the basics of concept switching with Keil C51.

Below is 2 -probably- simple questions, and will be pleased if you can share your valuable comments again.

1. If I use no reentrant functions, should I save the reentrant stack on context switching?

2. If several tasks are using reentrant functions (modifying the reentrant stack), I think I need different reentrant stack area (stack ptr) for each task. Otherwise, I cannot be sure that passive tasks' stack are not modified.

If this is true, how can I have different reentrant stack pointers ([IXP]_IBP) for each task? Is simply assigning a value on task entrance adequate?