Higher Half Kernel: Difference between revisions
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It is traditional and generally good to have your kernel mapped in every user process. Linux and many other Unices, for instance, reside at virtual addresses ''0xC0000000 - 0xFFFFFFFF'' of every address space, leaving the range ''0x00000000 - 0xBFFFFFFF'' for user code, data, stacks, libraries, etc.
Kernels that have such design are said to be "in the higher half" by opposition to kernels that use lowest virtual addresses for themselves, and leave higher addresses for the applications.
In addition, there is at least one non-x86 ISA (the [[MIPS Overview|MIPS]] [[User:Schol-r-lea/Understanding RISC vs CISC|RISC architecture]]) which partly forces the issue. on MIPS systems, addresses using the high bit (either bit 31 or bit 63, depending on the system word width) are reserved for use in Supervisor mode, and are exception trapped when in User mode.
Advantages of a higher half kernel are:
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