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From: LEICHTER-JERRY@YALE.ARPA
Newsgroups: comp.os.vms
Subject: Re: Problems defining MAIL$EDIT to be CALLABLE_TPU
Message-ID: <8708100445.AA25116@ucbvax.Berkeley.EDU>
Date: Mon, 10-Aug-87 00:45:35 EDT
Article-I.D.: ucbvax.8708100445.AA25116
Posted: Mon Aug 10 00:45:35 1987
Date-Received: Mon, 10-Aug-87 05:40:02 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: <LEICHTER-JERRY@YALE.ARPA>
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Organization: The ARPA Internet
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    ...Suppose one's private section file uses the TPU built-in CALL_USER to
    invoke some external routine whose identity is defined by the TPU$CALLUSER
    logical name.  That works fine normally, i.e., when invoking TPU directly
    from DCL via EDIT/TPU.  But when trying MAIL/EDIT, [with MAIL$EDIT defined
    as CALLABLE_TPU] the proper section file is picked up (i.e., properly
    translating TPUSECINI) but "it" doesn't seem to know about the
    TPU$CALLUSER definition and complains of (approximately) "error activating
    SYS$LIBRARY:TPU$CALLUSER.EXE" and then says something like "Could not find
    a routine for CALL_USER to invoke."
    
    In summary, "it" (i.e., callable_TPU (or somebody)), can translate
    TPUSECINI from the process table, but it seems unable to translate
    TPU$CALLUSER from the same table....

The MAIL image is installed with elevated privileges.  Such an image, when
it attempts to map a shareable image - either statically, by being linked
against it, or dynamically, using LIB$FIND_IMAGE_SYMBOL (which is what TPU
does to find your CALL_USER code) - is subject to two restrictions:

	- Only EXEC mode logicals are examined;
	- The shareable image found must itself be INSTALL'ed.

(The reason for this is security:  If I could cause MAIL to run my own code, I
could have it use MAIL's installed privileges - which include SYSPRV - to do
whatever I wanted to the system.  TPU section files don't contain executable
code as such - they are interpreted by TPU - so these restrictions don't
apply.)

I can't think of any work-arounds, other than using a spawned editor, or
INSTALL'ing image containing your CALL_USER code (which might be practical
in some situtations, e.g., a private workstation).
							-- Jerry
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