how to change from user mode to privileged mode

Discussion in 'iOS Development' started by ravi, Jan 6, 2016.

  1. ravi

    ravi Newbie

    I am running arm assembly code developed using XCODE on ios , i want to change from user mode to privileged mode to access some register in ARM v7 can any one help me
     
  2. So we start in user mode. To switch to kernel mode requires a privileged instruction. A privileged instruction must be done in kernel mode, therefore we must switch to kernel mode to enable switching to kernel mode.

    I'm thinking the system does not allow a user to switch itself to kernel mode directly, but that it is done by the kernel when the user seeks to execute another privileged instruction. Is that correct?
     
  3. damponting44

    damponting44 Banned

    In client mode you can't simply change to piece mode. Collaboration amongst client and part is done by means of framework calls. Every framework call is giving one characterized benefit. The client sends the administration name (ordinarily a number) and the required parameters. Here is a genuine illustration how this is finished. It's x86 AT&T style constructing agent.

    It moves the framework call name into the EAX enlist, the pointer to the parameters into the EBX enlist of the CPU and afterward transmits the product intrude on number 42. The intrude on taking care of will do the change to portion mode. The interfere with number is gazed upward in the Interrupt Descriptor Table (IDT) and conjures the capacity that is enlisted there, the syscall handler. This handler executes in piece mode. On come back to the client mode the code will move the substance of EAX into the variable ret.
     

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