Date: Tue, 4 Apr 2006 22:48:45 +1000 From: Andrew Reilly <andrew-freebsd@areilly.bpc-users.org> To: Scott Long <scottl@samsco.org> Cc: freebsd-amd64@freebsd.org Subject: Re: Status of NX bit support. Message-ID: <20060404124845.GA37816@gurney.reilly.home> In-Reply-To: <44319240.8070203@samsco.org> References: <44301C6D.3010206@rogers.com> <200604031442.43477.jhb@freebsd.org> <44318E3F.6080808@rogers.com> <20060403211943.GA99241@troutmask.apl.washington.edu> <44319240.8070203@samsco.org>
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On Mon, Apr 03, 2006 at 03:23:12PM -0600, Scott Long wrote: > Steve Kargl wrote: > >You're joking, right? How many registers are available for the > >i386? How many registers are available to an AMD64 cpu in > >64-bit mode? > > You also get less efficient cache utilization due to the wider data > types that are in use. It seems to be mostly a wash between the > advantages of more registers and the cost of lower cache efficiency. > amd64 is nice when you need more kernel address space and/or more > process address space. I know I'm probably being barking mad, here, but what I'd really like for my AMD64 workstation system is to be able to run it in AMD64-mode, but with 32-bit pointers. I vaguely remember reading some early AMD bumpf that that could be a supported configuration, somehow. Seems like it should just be a compiler switch, to specify 32-bit loads and stores for pointer values, and probably some checking in the pmap system to make sure that nothing is mapped outside the 32-bit range... Anyone know if it's been done? How it performs, if it's been done? I do a fair bit of DSP simulation work, and 64-bit long-longs are very handy to have go fast, and more registers and register-based calling conventions are always a good thing. I have no need for 64-bit addresses, at least at the process level, and I suspect that most workstation users would be in much the same boat... Didn't MIPS, Sun and Apple support such an arrangement on R4000+, SPARCv?8 and PowerPC970 (G5) systems? Cheers, -- Andrew
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