First, x86-64 also has “extensions” such as avx, avx2, and avx512. Not all “x86-64” CPUs support the same ones. And you get things like svm on AMD and avx on Intel. Remember 3DNow?
X86-64 also has “profiles” which tell you what extensions should be available. There is x86-64v1 and x86-64v4 with v2 and v3 in the middle.
RVA23 offers a very similar feature-set to x86-64v4.
You do not end up with a mess of extensions. You get RVA23. Yes, RVA23 represents a set of mandatory extensions. The important thing is that two RVA23 compliant chips will implement the same ones.
But the most important point is that you cannot “just use x86-64”. Only Intel and AMD can do that. Anybody can build a RISC-V chip. You do not need permission.
It's actually worst because intel is introducing APX now as well.
1. Yes, but most of the code would run on anything older than 2007. 20 years of stable ISA.
2. Also, fundamentally all modern CPUs are still 64-bit version of 80386. MMU, protection, low level details are all same.
This isn't really accurate, lots of commercial software is now compiled for newer x86 64 extensions.
If you're using OSS it doesn't really matter as you can compile it for whatever you want.
No, you really can’t. For some OSS, on hardware that has an OS supported by that software, with a compiler that supports that target and the options you want, and in some cases where the OSS has been written to support those options, you can compile it. Otherwise you are just out of luck.
I don't really understand your position here. Compiler availability isn't really that big of a deal, even on obscure or proprietary platforms. Why would there be "some cases where the OSS has been written to support those options"?
>Anybody can build a RISC-V chip. You do not need permission.
No, anybody can’t build a RISC-V chip. That’s the same mistake OSS proponents make. Just because something is open source doesn’t mean bugs will be found. And just because bugs are found doesn’t mean they will be fixed. The vast majority of people can’t do either.
The number of people who can design a chip implementation of the RISC-V ISA is much, much smaller, and the number who can get or own a FAB to manufacture the chips smaller still. You don’t need permission to use the ISA, but that is not the only gate.
I think it was clear that they were saying anybody is permitted to build a RISC-V chip, not that anybody has the skills.
> The number of people who can design a chip implementation
Thankfully you don't have to start from scratch. There are loads of open source RISC-V chip implementations you can start from.
> get or own a FAB to manufacture the chips
There is always FPGAs and also this:
https://fossi-foundation.org/blog/2020-06-30-skywater-pdk