While discussing workarounds for x86 processors that do not support the "cmpxchg8b" instruction, Linus Torvalds stated that it might be time to make the presence of this instruction mandatory for the kernel to work and drop support for i486 processors that do not support "cmpxchg8b" instead of trying emulate the operation of this instruction on processors that no one uses anymore. Currently, almost all Linux distributions that continue to support 32-bit x86 systems have switched to building the kernel with the X86_PAE option, which requires "cmpxchg8b" support.
According to Linus, from the point of view of kernel support, i486 processors have lost their relevance, despite the fact that they are still found in everyday life. At a certain point, processors become museum exhibits and it is quite possible for them to get by with βmuseumβ cores. Users who still have systems with i486 processors will be able to use LTS kernel releases, which will be supported for many years to come.
The cessation of support for classic i486s will not affect Intel's embedded Quark processors, which, although they belong to the i486 class, include additional instructions characteristic of the Pentium generation, including βcmpxchg8bβ. The same applies to Vortex86DX processors. Support for i386 processors was discontinued in the kernel 10 years ago.
Source: opennet.ru