Are Split Stacks Necessary on amd64?

Split Stacks on amd64

The concept of "split stacks" has been discussed regarding runtime optimizations. However, some experts argue that such techniques may be unnecessary on 64-bit architectures, particularly amd64.

Unnecessity on amd64

On 64-bit architectures like amd64, the virtual address space is significantly larger compared to 32-bit counterparts. This allows for millions of stack address ranges, each as large as an entire 32-bit address space.

Flat Memory Model and Stack Optimization

With the flat memory model used in modern systems, the operating system can allocate large chunks of virtual address space for stacks and map only the first page (4kB) to physical memory. As the stack grows, the OS dynamically remaps additional pages. By leveraging this feature, stacks can grow and shrink contiguously in virtual memory, resulting in efficient function prologues (code optimizations).

O(1) Stack Operations

Additionally, by tuning allocation thresholds based on principles like dynamic arrays, one can achieve an average complexity of O(1) for stack operations. This optimizes stack management while supporting a virtually無限 number of stacks that can expand to the desired size.

Conclusion

Based on these insights, it is true that split stacks are generally unnecessary on 64-bit architectures like amd64, as the larger virtual address space enables efficient stack management without the overhead of split stack techniques.

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