On 9/2/06, Kevin D. Kissell <KevinK@xxxxxxxx> wrote:
As Alan indicted, mechanisms for emulating single step behavior have long existed for MIPS and Linux. Newer MIPS parts which implement the EJTAG debug system do have a single-step mode, but they trap to Debug mode, rather than to the kernel - this allows kernel code to be single-stepped using an EJTAG probe. If the system allows for it - one needs to have ROM at the right location which transfers Debug mode control back to the kernel - it is possible to exploit EJTAG debug features from an OS kernel. We''ve prototyped this to prove that it works, but never went so far as to wire up EJTAG signle-step mode to a ptrace or other debug API. If for some strange reason the standard emulation mechanism isn't adequate for you (e.g. if your applicaiton is executing out of ROM), you do have this as a potential alternative. But it would not be a trivial hack.
Well this is ok ..but I am trying to implement kenel debugger.. something like system tap. And I have started with kprobe.. where the kernel code execution will be stopped at user specified address using break, how do i single step that instruction to decode the instruction and print the registers value..? ~Nida
