OSDev.org

sorry for my bad english plz

i loads a plain binary file at start of some page, then build page dir & page table, fill tss, add it to run by scheduler
when this code executes, if there is a loop, it loops for 400 times and then os crased when doing task switch

Then theres something wrong with your task switch code.

Be a little more specific about how you task switch. whats happening in your os and so on.
Do you have interrupts handlers setup for the 32 predefined ints from intel (for exception management). All they need do is print a message on screen and halt, just so you know abou they error.

Dangamoose.