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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.unix.wizards
Subject: Re: multiple-machine executables for Suns?
Message-ID: <24871@sun.uucp>
Date: Tue, 4-Aug-87 20:01:37 EDT
Article-I.D.: sun.24871
Posted: Tue Aug  4 20:01:37 1987
Date-Received: Thu, 6-Aug-87 07:05:38 EDT
References: <1853@megaron.arizona.edu> <12646@sol.hi.UUCP>
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> But more seriously, if I was going to design an a.out format that could
> "run" everywhere I would have the compilers, loaders, etc output a psuedo
> code and then have the kernal interpet the code.  This will keep the
> a.out small, but the will take FOREVER to execute. 

In a lot of UNIX systems, you already have that, and you don't have
to stuff the interpreter into the kernel, and thus can avoid the
effort of making large hunks of your kernel pageable or swappable
(you don't want that pseudo-code interpreter wired down, do you?) or
making those same hunks reloadable (you don't want to have to reboot
when you change the interpreter, right?).

The magic number is the string "#!"; just put the pathname of the
interpreter after that, and have the interpreter understand that its
first argument is the pathname of the file to be interpreted.  If the
interpreter takes flag arguments, you should have some flag that says
"no argument after this one is a flag, even if it begins with '-'"
and stick that after the name of the interpreter in the "#!"  line.
("/bin/sh" has the "-" argument; the 4.3BSD C shell has "-b".)

Of course, you can't safely use this for set-UID executables.  The
most obvious hole is closed by the above "this is the last argument"
flag, and changes in 4.3 that cause the script name NOT to be passed
as argv[0] fix the second-most-obvious hole; however, somebody
pointed a fairly obscure hole out to me that is fixable only by some
extra effort in the kernel, and there may be even more obscure holes
after that one.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com