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The kernel definitely sets the WIMG bits at https://github.com/torvalds/linux/blob/master/arch/powerpc/m... (line 336, if HN removes it), though I've never been able to "make it work" either.
I used box64 as a test case, where I had a game that would run in emulation, but only if I pinned it to a single core. On ARM64, it also worked, as the JIT translator on box64 uses manually inserted memory fences to force strongly ordered access.
The game never worked correctly, even after I patched the kernel to mark every page on the system as SAO, and confirmed this worked by checking the set memory flags. This might be a mistake in my understanding of what SAO should do, though. (or another failure in box64 on ppc64le)
One thought I've had recently is perhaps it's like the recently discovered tagged memory extension and only worked in big endian? There's nothing in the docs to suggest this, but since the only test case was BE-only, maybe?
> That may be true on the mach system call side, but the UNIX system calls don't appear to change.
They very much do, without warning, as the Go project discovered (after having been warned multiple times) during the Sierra betas: https://github.com/golang/go/issues/16272 https://github.com/golang/go/issues/16606
That doesn't mean Apple goes outs of its way to break syscalls (unlike microsoft), but there is no support for direct syscalls. That is why, again, you can't statically link libSystem.
> (Virgil actually does call the kernel directly).
That's completely unsupported ¯\_(ツ)_/¯