What is a Stack in C

A stack is a Last-In-First-Out (LIFO) data structure used to store temporary data like function calls, local variables, and return addresses. In embedded Linux, stacks are crucial for managing interrupt service routines (ISRs) and context switching.

Each process or thread has its own stack, and the kernel uses stacks to save and restore CPU state during interrupts.

Real-World Use Case

When an interrupt occurs:

• The CPU pushes the current context (registers, flags) onto the stack.
• The ISR executes using its own stack frame.
• After completion, the context is popped from the stack to resume normal execution.

This mechanism ensures safe and isolated execution of interrupt routines.

Advantages of Stack-Based Interrupt Handling

• Automatic context saving
• Isolated execution of ISRs
• Efficient memory usage
• Supports nested interrupts (with proper stack depth)

Common Pitfalls

• Stack Overflow: Too many nested calls or large local variables
• Corrupted Stack: Writing beyond bounds or misaligned access
• Improper ISR Design: Using blocking calls or dynamic memory in ISRs

Kernel-Specific Notes

• Kernel uses per-thread stacks (usually 8KB or 16KB)
• ISRs must be fast and non-blocking
• Avoid recursion and large local arrays in kernel space
• Use irqsave() and irqrestore() to manage interrupt flags safely

Conclusion

Understanding stack behavior in C is essential for writing safe and efficient interrupt handlers in embedded Linux. Proper stack usage ensures reliable context switching and system stability, especially in real-time applications.