78 lines
3.4 KiB
Plaintext
78 lines
3.4 KiB
Plaintext
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$NetBSD: README.dynamic,v 1.1 1995/02/13 21:39:01 cgd Exp $
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Currently, the NetBSD OSF/1 emulation code only supports statically
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linked OSF/1 binaries. This document is meant to be a quick
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description of what would need to happen to support dynamically linked
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OSF/1 binaries, and to provide an indication of the amount of work
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that would be required to add such support.
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To support dynamically linked OSF/1 binaries, three steps would have
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to be taken:
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(1) The osf1_exec_with_loader() syscall emulation code would
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have to be written.
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(2) Execve() would have to be changed to support invocation of
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a loader for dynamically linked binaries.
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(3) The pmap code would have to be extended to allow process
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virtual spaces that are much larger than are currently
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allowed.
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1. Implementing osf1_exec_with_loader().
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The description of osf1_exec_with_loader is as follows:
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int exec_with_loader(int flags, const char *loader,
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const char *file, char * const argv[],
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char * const envp[]);
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It invokes the program named by file, with the given argv and envp,
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by starting the specified loader (or /sbin/loader) and somehow passing
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the flags, file name, argv, and envp in such a way that the
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appropriate things will happen with them. This interface is
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completely undocumented (in the documentation that we have available),
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and so the only way to figure it out is to disassemble the OSF/1
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kernel and/or /sbin/loader.
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2. Changing execve() to support OSF/1 dynamically linked executables.
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Normally, dynamically linked executables are invoked using execve(),
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in the normal fashion. The kernel transforms that request into one
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that uses the loader, and causes the loader to be invoked with the
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appropriate information to run the target executable.
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The mechanism by which this is done is unknown; it may be possible to
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completely replace the OSF/1 loader with one designed for NetBSD, but
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that is rather prohibitive. (Additionally, it wouldn't solve the
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problem of needing to implement the osf1_exec_with_loader()
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functionality.)
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In any case, this would not be insignificant; it and/or the
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implementation of osf1_exec_with_loader() would probably require a
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complete rewrite or duplication of the current execve() code.
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3. Extending the pmap code to handle larger virtual spaces.
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OSF/1's /sbin/loader wants to be loaded at 0x3ff80000000. Currently,
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because of a simplifying assumption (specifically, to only use the
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first level-one pte for user-space mappings, effectively turning the
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pmap into one that looks much like one for a mc68030), only 8Gb
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(0x200000000 bytes) of user virtual space are supported.
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It is unclear that the extra virtual space is necessary for any
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applications that NetBSD/Alpha would be used for, and support for it
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would add a significant amount of complexity to the pmap module.
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Adding that support would probably require a from-scratch rewrite of
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the pmap module.
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Because of the difficulties in emulating the system call interface
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used to run dynamic executables, and the difficulties in allowing
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support for the address space the OSF/1 loader needs, I do not think
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that it is feasible to support dynamically linked OSF/1 executables
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with the OSF/1 loading mechanism. It may be possible to do so with a
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new loading mechanism which could be written for NetBSD, but it is
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unclear that the necessary interfaces to do even that could be
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discovered, and the effort required to implement a new loading
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mechanism would be prohibitive.
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-- cgd
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