During a discussion on 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 kernel operation and to discontinue support for i486 processors, which do not support 'cmpxchg8b', instead of trying to emulate the operation of this instruction on processors that are no longer used. Currently, almost all Linux distributions that continue to support 32-bit x86 systems have switched to kernel builds with the X86_PAE option, which requires support for 'cmpxchg8b'.
According to Linus, from the standpoint of kernel support, i486 processors have lost relevance, despite the fact that they are still encountered in everyday use. At a certain point, processors become museum pieces, and it is quite feasible to manage with 'museum' kernels. Users who still have systems with i486 processors will be able to use LTS kernel releases that will be supported for many more years.
The discontinuation of support for classic i486 will not affect the embedded processors Quark released by Intel, which, although belonging to the i486 class, include additional instructions characteristic of the Pentium generation, including 'cmpxchg8b'. The same applies to Vortex86DX processors. Support for i386 processors was discontinued in the kernel 10 years ago.
Source: opennet.ru
