[RTEMS Project] #2401: ARMv7M: Default exception handler doesn't support FPU

[RTEMS trac]

#2401: ARMv7M: Default exception handler doesn't support FPU
---------------------------+--------------------
 Reporter:  martin.galvan  |      Owner:
     Type:  defect         |     Status:  new
 Priority:  normal         |  Milestone:  4.11.1
Component:  cpukit         |    Version:  4.11
 Severity:  major          |   Keywords:
---------------------------+--------------------
 On exception entry, _ARMV7M_Exception_default stores the previous Stack
 Pointer
 in a CPU_Exception_frame. The SP can be MSP or PSP, depending on the mode
 in which the exception was taken. To know this, we must check the value of
 LR.

 Right now the code checks whether it should store MSP or PSP by comparing
 LR to
 -3 (0xFFFFFFFD). However, this doesn't work if we're using an FPU
 since the error code would be either 0xFFFFFFE9 or 0xFFFFFFED. The result
 is
 that we always end up selecting MSP.

 This bug was found by Sudarshan Rajagopalan in the RTEMS git master.

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Ticket URL: <http://devel.rtems.org/ticket/2401>
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