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Top Forums UNIX for Dummies Questions & Answers Advanced info on CPU Emulators Post 302530605 by Corona688 on Tuesday 14th of June 2011 12:01:46 PM
Old 06-14-2011
Quote:
Originally Posted by theKbStockpiler
Interpreted implies that the Emulator would just be substituting code for other code from a look-up table but then the program would actually be more or less ported at this point would it not?
It's hard to call something 'ported' when it can't run outside the emulator, no.

The exact approach may depend on the emulator in question. qemu, for instance, can use CPU virtualization features if you're emulating the same architecture you're on -- setting up a virtual environment in hardware. This lets programs run in the virtual environment mostly natively, just trapping a few higher-ring instructions and the like so software can take over and fill in the gaps. This was actually possible without hardware virtualization support, but it makes it much easier and more efficient -- I'm not too well read on the details but suspect it involves more direct/explicit ways for the client to talk to the host, for starters.

For emulators that run instructions that are completely alien to the native processor, the obvious way would be to make a data structure in memory that represents the registers of the native CPU, and use something like a big switch statement or look-up table to branch to the appropriate code for each instruction. If the emulated CPU has fewer registers than the native one I suppose you could stick everything in registers, use jump tables, self-modifying code, raw ASM and other dirty tricks to make it much faster but in the end it's the same idea.
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CPUSET(3)						   BSD Library Functions Manual 						 CPUSET(3)

NAME
cpuset_create, cpuset_destroy, cpuset_zero, cpuset_set, cpuset_clr, cpuset_isset, cpuset_size -- dynamic CPU sets SYNOPSIS
#include <sched.h> cpuset_t * cpuset_create(void); void cpuset_destroy(cpuset_t *set); void cpuset_zero(cpuset_t *set); int cpuset_set(cpuid_t cpu, cpuset_t *set); int cpuset_clr(cpuid_t cpu, cpuset_t *set); int cpuset_isset(cpuid_t cpu, const cpuset_t *set); size_t cpuset_size(const cpuset_t *set); DESCRIPTION
This section describes the functions used to create, set, use and destroy the dynamic CPU sets. This API can be used with the POSIX threads, see pthread(3) and affinity(3). The ID of the primary CPU in the system is 0. FUNCTIONS
cpuset_create() Allocates and initializes a clean CPU-set. Returns the pointer to the CPU-set, or NULL on failure. cpuset_destroy(set) Destroy the CPU-set specified by set. cpuset_zero(set) Makes the CPU-set specified by set clean, that is, memory is initialized to zero bytes, and none of the CPUs set. cpuset_set(cpu, set) Sets the CPU specified by cpu in set. Returns zero on success, and -1 if cpu is invalid. cpuset_clr(cpu, set) Clears the CPU specified by cpu in the CPU-set set. Returns zero on success, and -1 if cpu is invalid. cpuset_isset(cpu, set) Checks if CPU specified by cpu is set in the CPU-set set. Returns the positive number if set, zero if not set, and -1 if cpu is invalid. cpuset_size(set) Returns the size in bytes of CPU-set specified by set. SEE ALSO
affinity(3), pset(3), sched(3), schedctl(8), kcpuset(9) HISTORY
The dynamic CPU sets appeared in NetBSD 5.0. BSD
November 2, 2011 BSD
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