[kragen]

https://news.ycombinator.com/item?id=28683773 gives a useful way to employ them; Chicken Scheme has to run a minor garbage collection and longjmp to its trampoline before the stack runs out, but because there's no way to find out what the stack size limit is at runtime, you have to configure a stack size limit when you compile it. The CPython interpreter could also use them usefully; in order to ensure that recursive loops in Python programs raise a Python exception instead of segfaulting, it defaults to a limit of only 1000 levels of Python recursion, because some platforms it ran on were segfaulting at 2000. If it could query the stack size limit, it could instead raise an exception when it's getting close to the real limit instead of guessing. They wouldn't be like access().

There are more hacks in Heaven and Earth, Horatio, than are dreamed of in your philosophy.

[vasama]

I believe we were discussing a potential addition to the C standard. It would however be useless unless the standard also defined such things as stack layout and a closed set of operations which may consume more stack space, such as calling a function.

[kragen]

It's true that this potential addition to the C standard would not permit things like CPython or Chicken to depend only on the C standard, it's true, but then every C program already depends on things other than the C standard—such as the example given in TFA, that any C implementation is entitled to abort any C program because it ran out of stack.

Moreover, every nontrivial C program in practice contains UB.

Nevertheless, it does matter what is and isn't standardized; standardizing such functions would greatly improve the situation for programs like those I mention, because they would be able to rely on the C standard to find out when they're about to run out of stack, an event they already have code for handling. It's true that a pathological C library implementation could still totally break their stack-exhaustion-handling code, and in fact that's already true, but fortunately there are lots of C library implementations that behave well enough in practice.