libgreen's stack_bounds implementation includes the guard page

[jdm]

rust-mozjs uses the stack bounds to inform SpiderMonkey's conservative stack scanner, but it started segfaulting on the guard page after the most recent upgrade. Does it really make sense to include this page, or should we add some kind of usable_stack_bounds method?

[thestinger]

It needs a guard page, because it's the only thing stopping a stack overflow in C code called by Rust. The guard page will allow removing __morestack and using a more efficient scheme like the GCC -fcheck-stack instead.

[metajack]

Yes, obviously the guard page is needed. The question is should we report the guard page in the stack bounds. I think not, since obviously you aren't supposed to use that memory.

[thestinger]

Yeah, that makes sense.