Advanced info on CPU Emulators Post: 302530605

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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

06-14-2011

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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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LEARN ABOUT CENTOS

systemd-detect-virt

SYSTEMD-DETECT-VIRT(1)						systemd-detect-virt					    SYSTEMD-DETECT-VIRT(1)

NAME

       systemd-detect-virt - Detect execution in a virtualized environment

SYNOPSIS

       systemd-detect-virt [OPTIONS...]

DESCRIPTION

       systemd-detect-virt detects execution in a virtualized environment. It identifies the virtualization technology and can distinguish full VM
       virtualization from container virtualization.

       When executed without --quiet will print a short identifier for the detected virtualization technology. The following technologies are
       currently identified: qemu, kvm, vmware, microsoft, oracle, xen, bochs, chroot, uml, openvz, lxc, lxc-libvirt, systemd-nspawn.

       If multiple virtualization solutions are used, only the "innermost" is detected and identified. That means if both VM virtualization and
       container virtualization are used in conjunction, only the latter will be identified (unless --vm is passed).

OPTIONS

       The following options are understood:

       -h, --help
	   Prints a short help text and exits.

       --version
	   Prints a short version string and exits.

       -c, --container
	   Only detects container virtualization (i.e. shared kernel virtualization).

       -v, --vm
	   Only detects VM virtualization (i.e. full hardware virtualization).

       -q, --quiet
	   Suppress output of the virtualization technology identifier.

EXIT STATUS

       If a virtualization technology is detected, 0 is returned, a non-zero code otherwise.

SEE ALSO

       systemd(1)

systemd 208														    SYSTEMD-DETECT-VIRT(1)

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