Stewart Smith: Limiting functions to 32k stack in Drizzle (and scoped_ptr)
I wonder if this comes under “Code Style” or not…
Anyway, Monty and I finished getting Drizzle ready for adding “-Wframe-larger-than=32768″ as a standard compiler flag. This means that no function within the Drizzle source tree can use greater than 32kb stack – it’s a compiler warning – and with -Werror, it means that it’s a build error.
GCC is not perfect at detecting stack usage, but it’s pretty good.
Why have we done this?
Well, there is a little bit of recursion in the server… and we can craft queries to blow a small stack (not so good). On MacOS X, the default thread stack size is only 512kb. This gives not many frames if 32kb stack is a even remotely common.
I found some interesting places to throw a lot of things on the stack too – that would be rather far down on a callchain – leading to the possibility of blowing up in really strange ways.
We’d love to make it 16kb…. but that’s a fair bit more work, so something for the future.
We’ve used the Boost scoped_ptr to address a bunch of these situations as it provides pretty much minimal code change for the same effect (except that memory is dynamically allocated instead of as part of the stack frame).
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