On 32-bit ARM the fpexc system register is set by loadFpuState,
which includes the FPU enable/disable bit FPEXC_EN_BIT. This
register is part of the usercontext and needs to be initialised
correctly, otherwise the FPU will be disabled by loadFpuState.
Before, this bug was hidden because the FPU was enabled lazily
after a trap. This bug just caused one extra FPU trap at first
FPU use for each task: The first handleFPUFault would fail to
enable the FPU, causing another FPU trap when user space gets
restarted.
On the second FPU fault, switchLocalFpuOwner calls enableFpu first
and then calls saveFpuState because ksActiveFPUState is set to the
current task's FPU state. Then it gets saved with FPEXC_EN_BIT set
and the task can continue with the FPU actually enabled.
This also means that with the old code, the initial FPEXC state
of each task was equal to the previous active FPU task's.
Signed-off-by: Indan Zupancic <indan@nul.nu>
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