Operating Systems - System Call - Mechanism & Modes (User vs Kernel)
Consider a scenario where a user process makes a system call to allocate memory. Which of the following best describes the sequence of events and mode transitions?
Consider a scenario where a user process makes a system call to allocate memory. Which of the following best describes the sequence of events and mode transitions?
medium🧠🧾 Concept Trace Q4 of Q15
Step-by-Step Solution
Solution:
Step 1: User triggers system call via trap
User mode calls a function that traps to kernel mode for memory allocation.Step 2: Kernel allocates memory
Kernel performs allocation and returns a pointer.Step 3: CPU switches back to user mode
Control returns to user mode with allocated memory pointer.Final Answer:
Option D -> Option DQuick Check:
Memory allocation requires kernel intervention via trap, not direct user allocation. [OK]
Quick Trick: Memory allocation system calls trap to kernel, not direct user allocation [OK]
Common Mistakes:
MISTAKES- Assuming malloc() allocates kernel memory directly
- Believing kernel pre-allocates memory for all processes
- Thinking user mode sets flags to switch modes
Trap Explanation:
PITFALL- Candidates often confuse user library calls with kernel memory allocation and mode switches.
Interviewer Note:
CONTEXT- Evaluates understanding of system call flow for resource allocation.
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