[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] [PATCH] 32on64 call gate support
> -----Original Message----- > From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx] > Sent: 26 January 2007 10:14 > To: Petersson, Mats > Cc: Xen Development Mailing List > Subject: Re: [Xen-devel] [PATCH] 32on64 call gate support > > On 26/1/07 10:07 am, "Petersson, Mats" <Mats.Petersson@xxxxxxx> wrote: > > >> Do we know that anyone uses 64-bit call gates? I would > have thought it > >> unlikely. > > > > I agree, it's VERY unlikely that anyone uses call-gates in > 64-bit mode. > > There are other, better, ways to do system calls, including the > > dedicated SYSCALL instruction. Since 64-bit code is "new", > it's unlikely > > to use old ways of doing things "just because there was nothing else > > around at the time". > > Of course, it begs the question why call gates weren't > stripped from long > mode along with other ancient architectural baggage. Yeah, well... Actually, there may be a good reason for call-gates: If you use call-gates correctly, you could avoid having one arugment that is "which system call", but rather set up three dozen call-gates for your three-dozen system calls - so that may be what they were preserving it for, along with your suggestion below about old-OS support. There are a few more possible call-gates than other methods of system-call, even if they are not quite "unlimited". [Bear in mind that I'm NOT a chip-architect, so I don't know why they kept some things and removed others, aside from the "prefix" clean-up] > > Perhaps the idea was to allow compat-mode applications > relying on call gates > to be supported? So the OS would be responsible for > allocating 64-bit call > gates instead of 32-bit call gates? > > Anyhow, this is a bridge we should probably only cross if we > come to it. Definitely my opinion too. -- Mats > > -- Keir > > > > > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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