[PATCH] Implement variable-sized alloca instrumentation (take 2).

[Kostya Serebryany]

> > Note that number of allocas is not known statically so in general you'll need a dynamically growing array.

> 


Haha, no. 
While you don't know the number of allocas, their total size is limited by the size of the stack, 
so you can pre-allocate an array at the thread start up.

dynamically growing array in a hot spot in asan is not wise. 
We better allocate a bit extra space (maybe with MAP_NORESERVE)

So, maybe we simply use the existing fake stack (in use-after-return mode, or maybe even by default?) to simulate dynamic alloca?


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http://reviews.llvm.org/D7098

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