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SubjectRe: Is 386 processor still supported?
On Thu, 15 Jan 2009, Alan Cox wrote:

> > UP emulation of CMPXCHG and XADD for userland should be rather trivial,
> > so why not include it like with LL/SC for MIPS?
>
> Why not just ship an additional libc with the right options ?

Does not work for MIPS as glibc has no equivalent code for pre-LL/SC CPUs
and LL/SC is always used. For the i386 the situation seems worse yet as
for pre-i486 CPUs a generic C implementation of compare-and-exchange is
used guaranteeing silent thread unsafety. :(

IMO, a kernel emulation of CMPXCHG and XADD (both are used by
sysdeps/i386/i486/bits/atomic.h in glibc) with an optional LOCK prefix,
guaranteeing UP atomicity would be a cheap way to provide long-term i386
userland support with little burden for both Linux and respective user
software maintainers. Certainly it adds some bloat to the kernel, but I
think it is not an option that should be outright dismissed without
consideration.

Maciej


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