On Thu, Apr 02, 2009 at 10:58:54AM +0200, Luigi Rizzo wrote: > On Thu, Apr 02, 2009 at 11:48:33AM +0300, Kostik Belousov wrote: > > On Thu, Apr 02, 2009 at 09:06:05AM +0200, Luigi Rizzo wrote: > > > Hi, > > > I have some list manipulation algorithm that I would like to use > > > that relies rather centrally on atomic_cmpset_int(). > > > > > > This is an atomic instruction on 486+, but not available on 386 > > > and maybe other platforms. i386/atomic.h has a replacement > > > but it uses "pushfl; cli; ... popfl;" so it cannot run in userland. > > > > > > I was wondering if there is a good emulation for that instruction > > > on the i386 that is suitable for userland (other architectures > > > we support have a CPU instruction that does it, or in the case of ARM, > > > a usable emulation for userland). > > > > FreeBSD cannot boot on anything < 486, i.e. cmpxchgl and xaddl may be > > considered always supported by the CPU. > > It was a slightly more generic question -- this stuff is for userland > so while we can assume it works on modern FreeBSD versions, I would > like to see what constraints it has on older versions of FreeBSD. > Of course I can emulate the critical section with a pthread lock, > but that would be the worst case option. Support for FPU-less operations was removed from HEAD in Jul 2003. The support for i386+387 seems to be removed in 2004, i.e. before 5.x. The kernel explicitely requires working read-only mappings of the pages for kernel mode, AKA WP bit in CR0. Also, kernel assumes that cmpxchgl is always present. Do you want to support 4.x ?
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