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Re: Replacing malloc with alloca.


On 09/13/2015 12:28 PM, Florian Weimer wrote:
* Ajit Kumar Agarwal:

The replacement of malloc with alloca can be done on the following
analysis.

If the lifetime of an object does not stretch beyond the immediate
scope. In such cases the malloc can be replaced with alloca.  This
increases the performance to a great extent.

You also need to make sure that the object is small (less than a page)
and that there is no deep recursion going on.  Otherwise, the program
may no longer work after the transformation with real-world restricted
stack sizes.  It may even end up with additional security issues.
You also have to make sure you're not inside a loop. Even a small allocation inside a loop is problematical from a security standpoint.

You also need to look at what other objects might be on the stack and you have to look at the functional scope, not the immediate scope as alloca space isn't returned until the end of a function.

jeff


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