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This is related to this question . I'm not an expert on Linux device drivers or kernel modules, but I've been reading "Linux Device Drivers" [O'Reilly] by Rubini & Corbet and a number of online sources, but I haven't been able to find anything on this specific issue yet. When is a kernel or driver module allowed to use floating-point registers? If so, who is responsible for saving and restoring their contents? (Assume x86-64 architecture) If I understand correctly, whenever a KM is running, it is using a hardware context (or hardware thread or register set -- whatever you want to call it) that has been preempted from some application thread. If you write your KM in c, the compiler will correctly insure that the general-purpose registers are properly saved and restored (much as in an application), but that doesn't automatically happen with floating-point registers. For that matter, a lot of KMs can't even assume that the processor has any floating-point capability. Am I correct in guessing that a KM that wants to use floating-point has to carefully save and restore the floating-point state? Are there standard kernel functions for doing this? Are the coding conventions for this spelled out anywhere? Are they different for SMP-non SMP drivers? Are they different for older non-preemptive kernels and newer preemptive kernels?

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