[Bug libc/16291] feature request: provide simpler ways to compute stack and tls boundaries

["konstantin.s.serebryany at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16291

--- Comment #6 from Kostya Serebryany <konstantin.s.serebryany at gmail dot com> ---
(In reply to Ondrej Bilka from comment #5)
> Adding a thread-local variable with current bounds would be more

You mean, glibc can export thread-local variables for stack bounds and TLS
bounds?
That will be very convenient for us, but will consume some amount of TLS,
so if I were a glibc developer I would think twice. 


> appropriate. It is interesting from other reasons, for example deciding if
> memory should be allocated by alloca or malloc.

Hmm. Interesting indeed, although a bit scary. 
Suppose you have a deep recursion and before the recursion starts 
(i.e. you have plenty of stack) you decide to replace large malloc with alloca.
One should use this nice hack with caution. 

> 
> As performance is concerned you cannot do much better, as malloc already
> uses tls you can avoid that overhead.
> 
> Also how do you handle split-stacks? Its gcc feature that does more harm
> than good so do you support that?
I don't think anyone ever used split-stacks with AddressSanitizer, 
they will hardly work together.

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