Stack probing is kind of a weird thing though. I'm kind of surprised C++ compiler isn't doing that properly. Are they using inline assembly for speed?
The C++ compiler may or may not implement stack probing correctly, but this bug is in the Javascript JIT compiler. The fix is to make the JIT compiler update the stack pointer register each time through the loop so that if a page fault happens the kernel won’t see a huge amount of stack get allocated all in one go. Instead it’ll see several page faults each asking for a smaller amount which it is happy to grant.
See https://phabricator.services.mozilla.com/rMOZILLACENTRAL304d...
For the probing, according to the code:
// Can't push large frames blindly on windows, so we must touch frame memory
// incrementally, with no more than 4096 - 1 bytes between touches.
//
// This is used across all platforms for simplicity.
Edit: Or perhaps that is not the stack of the C++ program but rather than stack of the Javascript program.
So the code in this function is not performing the stack-probing, it generates code to perform it instead.
The one exception about sharing the same stack is that the first few iterations of a function run in an interpreter implemented in C++, and that interpreter has its own stack that we heap-allocate. This particular bug occurred during the transition from the C++ interpreter to JIT code.
Morally it's Google. Google is like Bitcoin. A huge natural ressource hog for a questionable benefit. Here the benefit is tracking users to make advertising billions. For that goal a billion of smart phones need several extra GB of memory an significantly larger batteries. What is the ecological footprint of that?
Typing on a seven year old smart phone with 2 GB (SailfishOS, so yes it is maintained. Maybe not perfectly, but better than many Androids half as old). It works quite well on reasonable pages even without add blocking. Of course super heavy pages won't work and for Google search I haven't even consented. Occasionally I get reminded of that when some site embeds it. Well, a good reminder for me not to use them.
It's very likely to have affected users on other websites, but Google is a common denominator for debugging.
My uneducated guess: they're using the Google Closure Compiler to make smaller JavaScript bundles. It saves some bandwidth and allows for better optimizations. It seems like a reasonable engineering decision to ensure product decisions don't affect the user experience too negatively, something a lot of us are familiar with..
But first building insanely heavy functionality and then optimizing it is not sustainable approach.
The background is of course that increasingly heavy function is moved into the client. Technically and especially economically this makes sense for Google. But the environmental footprint is outsourced to client devices. Greenwashing in a way. Avoidance of computing is a better solution than all types of optimizations. Not everything that is technically feasible is good for the planet and mankind.
That's bundling, not tree shaking. Tree shaking is an optional additional process during bundling where unreachable code is automatically removed.
This example had me remembering the discussion from earlier today about why modern code is so slow even though the machines are so fast. I doubt there were many Win32 programs that attempted to pass in 20,000 parameters to a function.