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Comment by drt1245 | Hacker News Reader

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drt1245

Recent versions of Debian require a 686.

https://www.debian.org/releases/stable/i386/ch02s01.en.html#...

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also, this video features a 486 cpu because linux dropped 386 support a while ago.

https://www.zdnet.com/article/good-bye-386-linux-to-drop-sup...

Anyone know what in particular the 486SX had that the 386 didn’t to make keeping only the former alive practical? Unfortunately the kernel mailing list link in the zdnet article appears to be rotted away.

I believe 386 did not have certain "atomic" instructions like CMPXCHG or XADD. So in order to support 386, the kernel had to have special versions of all locking primitives just for 386.

Here's a working link: http://lkml.iu.edu/hypermail/linux/kernel/1212.1/01152.html

From that link:

  x86, 386 removal: Remove CONFIG_CMPXCHG
  x86, 386 removal: Remove CONFIG_XADD
  x86, 386 removal: Remove CONFIG_BSWAP
  x86, 386 removal: Remove CONFIG_INVLPG
  x86, 386 removal: Remove CONFIG_X86_WP_WORKS_OK
  x86, 386 removal: Remove CONFIG_X86_POPAD_OK

Basic multitasking (CMPXCHG) and cache management instructions.

I was always under the impression that Linux 386 simply meant 32 bit support. So, no 386 support would mean no 32 bit support rather than the 386 specifically.

I have seen i386 being used in a couple of contexts. For example, Debian uses it to refer to the 32-bit port[1]. It also seemed to be used when various Linux distributions built Pentium optimized packages when that became a thing. In that case 386 would be used for earlier 32-bit processors and 686 would be used for later 32-bit processors. So the nomenclature is not always clear.

[1] https://www.debian.org/releases/stable/i386/

No, that's x86.

They dropped 386 support, but a 486 still works.

Would it be feasible to just build a Debian image for the i486? Few packages should depend on something newer.

Since the modern Linux kernel doesn't make any promises of 486 support there's very likely plenty of places inline assembly uses instructions unavailable on a 486.

So even if you compiled it with strict -march i486 you'd end up with unsupported instructions. Modern GCC also doesn't like emitting strict i386 or i486 code anymore so you'd be likely to end up with unsupported instructions even without any inline assembly.

I don't know offhand what instructions were introduced in Pentium or later.

Doing some googling... 486 had cmpxchg, that's good.

Seems it didn't have rdtsc. It's not out of the question, I might say even pretty common, for user mode code to use that one via inline asm to implement a timer.

Obviously no SIMD instructions. If they say they're supporting 686 or better they might have some compiler flags that depend on mmx or similar? SSE came late to P6.

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