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lab6 notes - Week 6 system call Processor modes Mode bit...

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Week 6 system call Processor modes Mode bit used to distinguish between execution on behalf of OS & execution on behalf of user Supervisor mode : processor can execute privileged instructions User mode : can onloy use subset of instructions Instruction sthat can execute in supervisor mode are supervisor, privileged, or protection instructions -I/O instructions are protected. If an application needs to do I/O, it needs to get the OS to do it on its behalf. _ instructions that can change the protections state of the system are privilegaes (e.g. process authorization staus, pointers to resourses.) Processor modes Mode bit may define areas of The kernel Part of system software exeuting in supervisor state Trusted software: implements protections mechanisms that could not be changed through actions of untrusted software in user space System calls User process requesting privileged operations provide by the OS
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Example system calls Include <unistd.h> Pid_t getpid (void); Retutns the process ID of the calling process
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