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Unformatted text preview: ad-only segment (.init, .text, .rodata) unused loaded from the executable file 0x08048000 0 Figure 8.11: Process address space. uses when it executes instructions on behalf of the process (e.g., when the application program executes a system call). 8.2.3 User and Kernel Modes In order for the operating system kernel to provide an airtight process abstraction, the processor must provide a mechanism that restricts the instructions that an application can execute, as well as the portions of the address space that it can access. Processors typically provide this capability with a mode bit in some control register that characterizes the privileges that the process currently enjoys. When the mode bit is set, the process is running in kernel mode (sometimes called supervisor mode). A process running in kernel mode can execute any instruction in the instruction set and access any memory location in the system. When the mode bit is not set, the process is running in user mode. A process in user...
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