EmbeddingGemma 2: an open, lightweight multimodal embedding model
deepmind.google·6d ago
AI Engineering
Hacker News·Aug 28·5 min read
How do functions like alloca allocate memory from the stack?
TL;DR
The _alloca function allocates memory on the stack by probing the stack space before adjusting the stack pointer. This ensures that large allocations do not bypass the guard page, preventing stack overflows.
✦ Why It Matters
Review your use of _alloca to ensure safe stack memory allocation in your applications.
Key Takeaways
- Use _alloca() for dynamic stack memory allocation.
- Always check stack size before large allocations.
- Understand the role of _chkstk() in memory safety.
- Avoid stack overflows by adhering to allocation limits.
How It Works
_alloca() allocates memory on the stack by first calling _chkstk() to probe the stack. This function checks if there is enough space for the requested allocation, ensuring that the guard page is not bypassed.
The assembly code illustrates the steps taken to create a local frame and allocate memory safely, demonstrating the importance of stack probing in preventing memory corruption.