Messages in this thread | | | Subject | Re: Various x86 syscall mechanisms | From | Andi Kleen <> | Date | Sat, 28 Jun 2008 07:00:02 +0200 |
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Roland McGrath <roland@redhat.com> writes: > > I think it is clearest to talk separately about the "intended ABI", the > "what actually works today", and the "why". (Also note I was not the > decision-maker in this, just picking up what I can see.)
You are correct.
> For the 32-bit ABI, what I believe was always the intent for what could be > considered the proper ABI is "int 0x80" or "use the vDSO entry point". If > someone asked me what you could ever have expected to rely on for the > future, I would say exactly that. The use of the vDSO is explicitly > intended to take the details of sysenter/syscall or other such new > instructions out of the 32-bit ABI picture for what any proper application > will expect from the kernel.
For SYSENTER the vDSO is even needed because it relies on a hardcoded return address.
> AMD's were the first x86_64 CPUs, and those always supported "syscall" > from 32-bit tasks to 64-bit kernels. (I don't know whether AMD CPUs now > support "sysenter" from 32-bit tasks to 64-bit kernels, and if so which > past AMD64 CPUs may not have supported that. On today's kernel you could
K8 at least.
> It was long on my back-burner list to toss in the "syscall" version of the > 32-bit vDSO for 32-bit kernels on hardware that supports "syscall". But,
That would only make a difference on K6 (K7 supports SYSENTER), and also K6/K7 SYSCALL was slightly different from the K8 version.
-Andi
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