16 ms·
> The jitter entropy technique relies on differences in timing when running the same code, which requires both a high-resolution CPU cycle counter and a CPU tha
by davikr 3y ago
> The jitter entropy technique relies on differences in timing when running the same code, which requires both a high-resolution CPU cycle counter and a CPU that appears to be nondeterministic (due to caching, instruction reordering, speculation, and so on). There are some architectures that do not provide that, however, so no entropy can be gathered that way. Donenfeld noted that non-Amiga m68k systems, two MIPS models (R6000 and R6000A), and, possibly, RISC-V would be affected;
So, I understand not wanting to break RISC-V support, but _should_ people really care about breaking compatibility with early 1990s MIPS chips and a 1979 Motorola CPU?
- phone8675309 3y agoClearly Linus and the maintainers of those architectures care enough not to break them (and those architecture maintainers have enough clout to be taken seriously). How old does a CPU need to be in order to no longer be supported? The 32-bit x86 architecture is nearly 40 years old - should it be retired for being too old?
- dspillett 3y ago> The 32-bit x86 architecture is nearly 40 years old - should it be retired for being too old? Parts of it already are, from a Linux point of view anyway. It looks like the mainline kernel will drop support for 486 family chips after 6.x, and support for the 386 was dropped in 3.8 (back in 2012). Some distributions already don't release a version for 32-bit-only intel/amd architectures. It'll be a long time before x86 support is dropped in its entirety, but even today you already have less choice than if you run something not sporting an amd64 or arm compatible architecture.
- jorvi 3y ago> The 32-bit x86 architecture is nearly 40 years old - should it be retired for being too old? I’m sure there is some way to gather architectural usage numbers + their likelihood of upgrading, roll it into a value, and if that value drops below X, that architecture gets left behind. The reason why I mention likelihood of upgrade is that there is a gigantic amount of MIPS routers running Linux, but virtually all of them are stuck on old kernels and very unlikely to be upgraded. I’m sure other architectures have similar snags.
- voakbasda 3y agoThey mostly run old kernels because their vendors do not keep them up to date, and the community does not have champions willing to upstream support for them. In theory it should still be entirely possible to refresh those devices with a modern kernel and user space. Patches would likely be welcomed upstream as well.
- pavon 3y agoYeah, it doesn't make sense to talk about the m68k being a 1979 processor, when Motorola continued to develop it and release new chips all through the 80's, and it continued to be used in new Mac and Next computers up through the early 90's. The 80486 would be its peer as far as obsolescence goes, not the 8086. But like others mentioned even the i486 is about to lose Linux support.
- cratermoon 3y agoThe PowerPC architecture is 32 years old, yet it still lives in, among other forms, the RAD750, which powers things like JWST, Perseverance and Curiosity rovers, Juno, LRO, and MRO. Reports say the RAD750 costs about $200K US
- LanzVonL 3y agoWhy shouldn't people expect Linux to run on ancient computers? I guess this is why we have NetBSD.
- rollcat 3y agoMac/PPC user here. The right thing to do is to support the 99% use case best you can, and leave dealing with the quirks of ancient garbage^W^W these wonderful machines of times past to the enthusiasts. If you want to e.g. make use of modern crypto, the slow CPU is a far bigger issue than sourcing the random numbers.
- Palomides 3y agothere are almost certainly new-ish low end ARM chips this would hit as well, it's not really about the specific examples declaration of bias: I have a non-Amiga m68k that can run linux
- dmitrygr 3y ago> So, I understand not wanting to break RISC-V support, but _should_ people really care about breaking compatibility with early 1990s MIPS chips and a 1979 Motorola CPU? Yes, we care a lot more than about the 2020 MIPS incarnation (you young kids call it RISCV, fooling nobody)
- snvzz 3y agoRISC-V resembles RISC and RISC-2 much more closely than it does MIPS. MIPS was inspired by RISC, not the other way around.
- snvzz 3y agoIn reality, there's no reason there cannot be two implementations, with the correct one automatically selected on build according to architecture.
- jasonwatkinspdx 3y agom68k variants were quite popular in the embedded world until fairly recently.
- snvzz 3y agoThey will still stay around for a while. There's also Renesas Rx, an ISA heavily inspired by m68k. But even Renesas is shifting to RISC-V, sensibly so.