Changes between Version 37 and Version 38 of GSoC/2013/ParavirtualizationOfRTEMS

Sep 17, 2013, 5:47:41 PM (6 years ago)

/* Implementation */


  • GSoC/2013/ParavirtualizationOfRTEMS

    v37 v38  
    292292=  Implementation  =
    294 =  Issues  =
    296 This section deals with implementation issues, which occurred during the implementation process.
    297  *  No console write in POK.
     294=  Virtualization layer (POK)  =
     296The virt. layer is implemented in the user code part of the partitions code.
     297Mostly, it only makes a syscall and passes the arguments through.
     299=  libpart.a creation (POK)  =
     301libpart.a is build after libpok.a but with the same makefile rule.
     302libpart.a consists of libpok.a plus the objects from the user code files.
     304=  Interrupt design (POK)  =
     306I redesigned the interrupt handling in POK.
     307Previously there was no way of knowing which interrupt number occurred, as the IDT directly invoked the corresponding handler.
     308I replaced all 16 hardware interrupt handlers with predefined handlers, which know their interrupt number.
     309Then a meta handler is called to look up the registered handlers for this vector number and invokes first a kernel handler and then the partition handlers.
     310The lookup table is an array consisting of objects which have fields for the vector number, the handler list for the number of configured partitions plus one (kernel) and a list to indicate if the partition is waiting for an interrupt.
     311The waiting flag is necessary, because a partition needs to process the interrupt before a new one can be delivered.
     313To register a handler I introduced new syscalls with POK to register and unregister a handler, to enable and disable interrupt delivery to the partition and to acknowledge an interrupt.
     314The acknowledge syscall sets the waiting flag mentioned above.
     316The functions corresponding to these syscalls are implemented in the x86 bsp.c file.
     317There is a new pok_bsp_irq_register_hw function, which is only accepting IRQ values for the hardware IRQ lines (0-15).
     318pok_bsp_irq_register cannot be used to register IRQ handlers for hardware IRQs.
     320=  Remaining Issues  =
     321==  Forwarding interrupts to user space handlers  ==
     324The transition to user space proved very challenging.
     325I was not able to implement it in a reliable way.
     326In my design I will only make the transition to user space once.
     327The kernel stack will be cleaned up, after the transition, so no memory leaks will occur there.
     328To make this transition the interrupted context and the vector is passed to the user space handler, which is responsible to find the right handler for this interrupt number and before it returns to the point of interruption it has to restore the register and stack state.
     329The return instruction of the handler is used to pop the interrupted EIP from the stack.
     330Then the user space shall proceed like no interrupt occurred.
     332This doesn't work well.
     333This is implemented with manual stack manipulation and magic values to find the data on the stack.
     334This leads to GPF (0xd) as the EIP is pointing to invalid instructions.
     335This needs debugging - but GDB is of no help, because it can't handle segmentation.
     336At time of writing, I need to write documentation before I can go back to debugging.
    298337=  References  =