4 ms·

Posts like this showcase how malleable Linux really is without getting overly complicated to follow. Really a nice quick read.

ianlevesque 6y ago
Yeah slightly tangential but I wonder if some of the alternative OSes (looking at you Haiku) could just use Linux as the kernel for portability.
- boogies 6y ago
  That would be great if people could admit that the kernel isn't the operating system.
  - yjftsjthsd-h 6y ago
    Of course the kernel isn't the OS, but it's a big chunk of it, and defines building blocks (and constraints) that the upper layers use.
zozbot234 6y ago
But not nearly as malleable as it could be. Hopefully, true 80386 support can be reintroduced to the kernel in a way that keeps it properly self-contained and easy to support. There are also a few kernel-tinification approaches floating around that could make the kernel smaller and easy to fit in a floppy-using scenario.
- djxfade 6y ago
  But why? What "real" hardware would actually have any use for it today? I understand that it might be fun, but I don't see the practical use case for it.
  - nemetroid 6y ago
    The 737 Max? It uses an 80286, so it’s even older. I'm also curious what use it would have. I imagine in cases where you're tied to such old hardware, you would also be tied to old software.
    - skissane 6y ago
      > The 737 Max? It uses an 80286, so it’s even older. If we are talking about the computer that runs MCAS, my understanding is that it isn't a 286, it is a Rockwell Collins FCC-730 (aka EDFCS-730). The FCC-730 is a proprietary custom CPU architecture, there is limited public info available on it, although I did read somewhere that it uses a stack machine architecture (like Burroughs mainframes, classic HP 3000, Tandem T-16, various "Forth on a chip" processors, etc)
      - nemetroid 6y ago
        To be pedantic, FCC-730 is the name of the Flight Control Computer itself. Its CPU may or may not be a 286. It has however been speculated that it is, as discussed here: https://news.ycombinator.com/item?id=20380523 https://news.ycombinator.com/item?id=20380523.
        skissane 6y ago
        I agree, the FCC-730/EDFCS-730 is not the name of the CPU, it is the name of the computer. According to the diagrams in US patent 7,852,235 [1], the FCC-730 CPU is an FCP-2002. I would caution against the possibly mistaken inference that this patent describes the actual architecture of the 737-MAX or any other actual flight computer, as opposed to simply a design that Rockwell-Collins may have developed and not (yet) actually deployed. In particular, while the 737-MAX does have an FCC-730, I don't think it has an IPS-5000. A NASA Langley presentation [2] mentions formal verification of the FCP-2002. I think that if it is formally verified, it is probably not a 286. A 286 would be a poor choice for a formally verified microprocessor for embedded applications since it has a huge number of extraneous features that would complicate the verification process while yielding no benefit for the embedded application. The presentation also mentions a new "FCS 5000" product line, and its formal verification, and I wonder if that has any connection with the IPS-5000 CPU card mentioned in the patent diagram? Probably, the patent describes a new flight control computer design, meant as a successor to the design used in the 737-MAX (and other Boeing aircraft such as the 777). The Boeing 777 autopilot uses FCP 2002 CPUs as well [3] I swear I read somewhere that the FCP 2002 had a stack machine architecture, but now I can't find where I read that. (Did I imagine reading it?) I'm not sure where this "286" stuff comes from. I think maybe, FCP-2002 is a 16-bit CPU, and then people say a 16-bit CPU is "like a 286", and then maybe that gets corrupted in the retelling, and "like a 286" turns into "a 286"? [1] https://patents.google.com/patent/US7852235B1 https://patents.google.com/patent/US7852235B1 [2] https://shemesh.larc.nasa.gov/NFM2018/talks/Butler.pdf https://shemesh.larc.nasa.gov/NFM2018/talks/Butler.pdf [3] https://web.archive.org/web/20100822151603/http://www.rockwellcollins.com/ecat/AT/AFDS-770.html https://web.archive.org/web/20100822151603/http://www.rockwe...
- JoshTriplett 6y ago
  > Hopefully, true 80386 support can be reintroduced To the best of my knowledge, nobody is making new 386-only chips (that have no 486 or 586 support). As long as that remains the case, hopefully that support stays removed. > There are also a few kernel-tinification approaches floating around that could make the kernel smaller and easy to fit in a floppy-using scenario. We could always use more people looking at the size regressions, and working on making more kernel components optional. If anyone is interested in working on this, send me email and I'd be happy to get you connected with it.
- jfkebwjsbx 6y ago
  No, it will not be reintroduced. There is no use for it. That belongs in a fork.
- cesarb 6y ago
  > Hopefully, true 80386 support can be reintroduced to the kernel in a way that keeps it properly self-contained and easy to support. The merge which removed the 80386 support (https://git.kernel.org/torvalds/c/743aa456c1834f76982af44e8b71d1a0b2a82e21 https://git.kernel.org/torvalds/c/743aa456c1834f76982af44e8b...) stated as the reason "[...] complexity has plagued us with extra work whenever we wanted to change SMP primitives, for years." That is, it was not easy to keep it self-contained. Every new SMP primitive has to be implemented and maintained for all the architectures supported by the kernel, and the original 80386 ISA was too limited. Not to mention that the 80386 didn't honor the write-protect bit in the page tables while in the kernel (https://git.kernel.org/torvalds/c/a5c2a893dbd4956a72fb261e8790d19f67b52c99 https://git.kernel.org/torvalds/c/a5c2a893dbd4956a72fb261e87...), with consequences all over the kernel (https://git.kernel.org/torvalds/c/96d4f267e40f9509e8a66e2b39e8b95655617693 https://git.kernel.org/torvalds/c/96d4f267e40f9509e8a66e2b39...).
  - zozbot234 6y ago
    Were 80386 SMP systems really all that common to begin with? Perhaps 80386 support should just focus on the uniprocessor case, at least as a start.
- dredmorbius 6y ago
  There's Alan Cox's Fuzix which runs on 68000, Z80, and 8080 CPUs, among others. http://www.fuzix.org http://www.fuzix.org
- Koshkin 6y ago
  There are perfectly good older versions of Linux that will support i386 forever. (Not to mention FreeDOS.)

ianlevesque 6y ago

Yeah slightly tangential but I wonder if some of the alternative OSes (looking at you Haiku) could just use Linux as the kernel for portability.

boogies 6y ago
That would be great if people could admit that the kernel isn't the operating system.
- yjftsjthsd-h 6y ago
  Of course the kernel isn't the OS, but it's a big chunk of it, and defines building blocks (and constraints) that the upper layers use.

zozbot234 6y ago

But not nearly as malleable as it could be. Hopefully, true 80386 support can be reintroduced to the kernel in a way that keeps it properly self-contained and easy to support. There are also a few kernel-tinification approaches floating around that could make the kernel smaller and easy to fit in a floppy-using scenario.

djxfade 6y ago
But why? What "real" hardware would actually have any use for it today? I understand that it might be fun, but I don't see the practical use case for it.
- nemetroid 6y ago
  The 737 Max? It uses an 80286, so it’s even older. I'm also curious what use it would have. I imagine in cases where you're tied to such old hardware, you would also be tied to old software.
  - skissane 6y ago
    > The 737 Max? It uses an 80286, so it’s even older. If we are talking about the computer that runs MCAS, my understanding is that it isn't a 286, it is a Rockwell Collins FCC-730 (aka EDFCS-730). The FCC-730 is a proprietary custom CPU architecture, there is limited public info available on it, although I did read somewhere that it uses a stack machine architecture (like Burroughs mainframes, classic HP 3000, Tandem T-16, various "Forth on a chip" processors, etc)
    - nemetroid 6y ago
      To be pedantic, FCC-730 is the name of the Flight Control Computer itself. Its CPU may or may not be a 286. It has however been speculated that it is, as discussed here: https://news.ycombinator.com/item?id=20380523 https://news.ycombinator.com/item?id=20380523.
      - skissane 6y ago
        I agree, the FCC-730/EDFCS-730 is not the name of the CPU, it is the name of the computer. According to the diagrams in US patent 7,852,235 [1], the FCC-730 CPU is an FCP-2002. I would caution against the possibly mistaken inference that this patent describes the actual architecture of the 737-MAX or any other actual flight computer, as opposed to simply a design that Rockwell-Collins may have developed and not (yet) actually deployed. In particular, while the 737-MAX does have an FCC-730, I don't think it has an IPS-5000. A NASA Langley presentation [2] mentions formal verification of the FCP-2002. I think that if it is formally verified, it is probably not a 286. A 286 would be a poor choice for a formally verified microprocessor for embedded applications since it has a huge number of extraneous features that would complicate the verification process while yielding no benefit for the embedded application. The presentation also mentions a new "FCS 5000" product line, and its formal verification, and I wonder if that has any connection with the IPS-5000 CPU card mentioned in the patent diagram? Probably, the patent describes a new flight control computer design, meant as a successor to the design used in the 737-MAX (and other Boeing aircraft such as the 777). The Boeing 777 autopilot uses FCP 2002 CPUs as well [3] I swear I read somewhere that the FCP 2002 had a stack machine architecture, but now I can't find where I read that. (Did I imagine reading it?) I'm not sure where this "286" stuff comes from. I think maybe, FCP-2002 is a 16-bit CPU, and then people say a 16-bit CPU is "like a 286", and then maybe that gets corrupted in the retelling, and "like a 286" turns into "a 286"? [1] https://patents.google.com/patent/US7852235B1 https://patents.google.com/patent/US7852235B1 [2] https://shemesh.larc.nasa.gov/NFM2018/talks/Butler.pdf https://shemesh.larc.nasa.gov/NFM2018/talks/Butler.pdf [3] https://web.archive.org/web/20100822151603/http://www.rockwellcollins.com/ecat/AT/AFDS-770.html https://web.archive.org/web/20100822151603/http://www.rockwe...
JoshTriplett 6y ago
> Hopefully, true 80386 support can be reintroduced To the best of my knowledge, nobody is making new 386-only chips (that have no 486 or 586 support). As long as that remains the case, hopefully that support stays removed. > There are also a few kernel-tinification approaches floating around that could make the kernel smaller and easy to fit in a floppy-using scenario. We could always use more people looking at the size regressions, and working on making more kernel components optional. If anyone is interested in working on this, send me email and I'd be happy to get you connected with it.
jfkebwjsbx 6y ago
No, it will not be reintroduced. There is no use for it. That belongs in a fork.
cesarb 6y ago
> Hopefully, true 80386 support can be reintroduced to the kernel in a way that keeps it properly self-contained and easy to support. The merge which removed the 80386 support (https://git.kernel.org/torvalds/c/743aa456c1834f76982af44e8b71d1a0b2a82e21 https://git.kernel.org/torvalds/c/743aa456c1834f76982af44e8b...) stated as the reason "[...] complexity has plagued us with extra work whenever we wanted to change SMP primitives, for years." That is, it was not easy to keep it self-contained. Every new SMP primitive has to be implemented and maintained for all the architectures supported by the kernel, and the original 80386 ISA was too limited. Not to mention that the 80386 didn't honor the write-protect bit in the page tables while in the kernel (https://git.kernel.org/torvalds/c/a5c2a893dbd4956a72fb261e8790d19f67b52c99 https://git.kernel.org/torvalds/c/a5c2a893dbd4956a72fb261e87...), with consequences all over the kernel (https://git.kernel.org/torvalds/c/96d4f267e40f9509e8a66e2b39e8b95655617693 https://git.kernel.org/torvalds/c/96d4f267e40f9509e8a66e2b39...).
- zozbot234 6y ago
  Were 80386 SMP systems really all that common to begin with? Perhaps 80386 support should just focus on the uniprocessor case, at least as a start.
dredmorbius 6y ago
There's Alan Cox's Fuzix which runs on 68000, Z80, and 8080 CPUs, among others. http://www.fuzix.org http://www.fuzix.org
Koshkin 6y ago
There are perfectly good older versions of Linux that will support i386 forever. (Not to mention FreeDOS.)