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2. For each of the three mechanisms for supporting dual mode operation |
privileged instructions, memory protection, and timer interrupts | ex-
plain what might go wrong without that mechanism, assuming the system
still had the other two.
3. Suppose we had a perfect object-oriented language and compiler, so that
only an object's methods could access the internal data inside an object.
If the operating system only ran programs written in that language, would
it still need hardware memory address protection?
4. Suppose you are tasked with designing the security system for a new
web browser that supports rendering web pages with embedded web page
scripts. What checks would you need to ensure that executing buggy or
malicious scripts could not corrupt or crash the browser?
5. Define three styles of switching from user-mode to kernel-mode, and four
styles of switching from kernel-mode to user-mode.
6. A typical hardware architecture provides an instruction called return from
interrupt, abbreviated by something like iret. This instruction switches
the mode of operation from kernel-mode to user-mode. This instruction
is usually only available while the machine is running in kernel-mode.
a. Explain where in the operating system this instruction would be used.
b. Explain what happens if an application program executes this in-
struction.
7. A hardware designer argues that there are enough transistors on the chip
to provide 1024 integer registers and 512 floating point registers, so that
the compiler almost never needs to store anything on the stack. You have
been invited as the operating system guru to give an opinion on the new
design.
a. What is the effect of having such a large number of registers on the
operating system?
b. What additional hardware features you would recommend adding to
the design above?
c. What happens if the hardware designer also wants to add a 16-station
pipeline into the CPU, with precise exceptions. How would that affect
the user-kernel switching overhead?
8. Which of the following components is responsible for loading the initial
value in the program counter for an application program before it starts
running: the compiler, the linker, the kernel, or the boot ROM?
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