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POWhat are coding conventions for using floating-point in Linux device drivers?
 

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  1. POWhat are coding conventions for using floating-point in Linux device drivers?
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    <p>This is related to <a href="https://stackoverflow.com/questions/431045/linux-device-driver-unsave-fxsave-fxrstor-bug-any-precedents">this question</a>.</p> <p>I'm not an expert on Linux device drivers or kernel modules, but I've been reading "Linux Device Drivers" [O'Reilly] by Rubini &amp; Corbet and a number of online sources, but I haven't been able to find anything on this specific issue yet.</p> <p>When is a kernel or driver module allowed to use floating-point registers? <BR> If so, who is responsible for saving and restoring their contents? <BR> (Assume x86-64 architecture) </p> <p>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.</p> <p>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?</p> <p>Are the coding conventions for this spelled out anywhere?<BR> Are they different for SMP-non SMP drivers? <BR> Are they different for older non-preemptive kernels and newer preemptive kernels?</p>
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