Add binaryen option --add-stack-limit-global

[juj]

Add binaryen option --add-stack-limit-global to enable controlling when to emit the stack limit global variable to the wasm module.

[kripken]

This should be controlled by the emscripten ASSERTIONS flag - is that not good enough for some reason?

[juj]

This is for release builds. We want to have ability to check free stack space, but not emit runtime stack checks or other debug code.

[kripken]

We want to have ability to check free stack space

Oh, can't you do that with stackSave() already? That gets the current stack location. Then you have STACK_BASE and STACK_MAX which is the valid range for it.

[sbc100]

Hopefully a lot of this will not be necessary in emscripten-core/emscripten#11166 lands.

After this change it should be possible to these two new functions as aliases that live in system/lib/compiler-rt/stack_ops.s which can then be exported as needed via EXPORTED_FUNCTIONS.

The alias syntax in the .s format is:

.set alias_of_foo, foo

[juj]

Oh, can't you do that with stackSave() already?

I was not able to call stackSave() from C code, that did not seem possible, although with Sam's assembly code that would become a possibility?

Then you have STACK_BASE and STACK_MAX which is the valid range for it.

Also was not able to access these from within wasm, without having to jump out to JS.

[sbc100]

Oh, can't you do that with stackSave() already?

I was not able to call stackSave() from C code, that did not seem possible, although with Sam's assembly code that would become a possibility?

Yes, as of, #11166 you should now be able to call stackSave() and friends from the C code.

Then you have STACK_BASE and STACK_MAX which is the valid range for it.

Also was not able to access these from within wasm, without having to jump out to JS.

[juj]

This was resolved in another way earlier, so no longer relevant.