alt Hacker News> You're holding it wrong. Perhaps you've been holding it wrong for so long and so confidently that you've distorted the world around you -- indeed on MSVC on x86 or x86-64 that actually happened -- but, you're still holding it wrong.
Please explain. How would you make the variable backed by a hardware register region? Is this using some sort of linker trick to change where the value lives in memory?
You said it was for concurrency. The feature you want for that in C (and most languages suitable for this problem) is atomic memory ordering, not the volatile type qualifier.
Microsoft's platform was x86 only for years, and because Intel's design pays for a lot more memory ordering by default than most, on Microsoft's platforms just "volatile" would kinda work even though it was the wrong thing, so Microsoft explicitly grandfathered this for x86 and x86-64 only, you are guaranteed the Acquire-Release ordering even though you didn't ask for it with your volatile type qualifier.
If you were actually thinking of POSIX signals or something similar then yeah, the POSIX requirements say volatile will work, seems like a bad idea to me, but your compiler and other tools are likely also built for POSIX so they've read the same documentation.