October 2000
Intermediate to advanced
704 pages
18h 13m
English
Content preview from Understanding the Linux Kernel
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19.3. Execution Domains
As mentioned in Chapter 1, a neat feature of Linux is its ability to execute files compiled for other operating systems. Of course, this is possible only if the files include machine code for the same computer architecture on which the kernel is running. Two kinds of support are offered for these "foreign" programs:
Emulated execution: necessary to execute programs that include system calls that are not POSIX-compliant
Native execution: valid for programs whose system calls are totally POSIX-compliant
Microsoft MS-DOS and Windows programs are emulated: they cannot be natively executed, since they include APIs that are not recognized by Linux. An emulator like DOSemu or Wine (which appeared in the example at the end of the previous section) is invoked to translate each API call into an emulating wrapper function call, which in turn makes use of the existing Linux system calls. Since emulators are mostly implemented as User Mode applications, we don't discuss them further.
On the other hand, POSIX-compliant programs compiled on operating systems other than Linux can be executed without too much trouble, since POSIX operating systems offer similar APIs. (Actually, the APIs should be identical, although this is not always the case.) Minor differences that the kernel must iron out usually refer to how system calls are invoked or how the various signals are numbered. This information is stored in execution domain descriptors of type exec_domain.
A process specifies ...
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