alt Hacker News> Show me somebody who calls the IBM S/360 a RISC design, and I will show you somebody who works with the s390 instruction set today.
Ahaha so true.
But to answer the post's main question:
> Why do we even have linear physical and virtual addresses in the first place, when pretty much everything today is object-oriented?
Because backwards compatibility is more valuable than elegant designs. Because array-crunching performance is more important than safety. Because a fix for a V8 vulnerability can be quickly deployed while a hardware vulnerability fix cannot. Because you can express any object model on top of flat memory, but expressing one object model (or flat memory) in terms of another object model usually costs a lot. Because nobody ever agreed of what the object model should be. But most importantly: because "memory safety" is not worth the costs.
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But we don't have a linear address space, unless you're working with a tiny MCU. For last like 30 years we have virtual address space on every mainstream processor, and we can mix and match pages the way we want, insulate processes from one another, add sentinel pages at the ends of large structures to generate a fault, etc. We just structure process heaps as linear memory, but this is not a hard requirement, even on current hardware.
What we lack is the granularity that something like iAPX432 envisioned. Maybe some hardware breakthrough would allow for such granularity cheaply enough (like it allowed for signed pointers, for instance), so that smart compilers and OSes would offer even more protection without the expense of switching to kernel mode too often. I wonder what research exists in this field.