From:	CSBVAX::MRGATE!@KL.SRI.Com:leichter-jerry@yale-venus.ARPA@SMTP  9-AUG-1987 22:12
To:	EVERHART
Subj:	Re: Problems defining MAIL$EDIT to be CALLABLE_TPU

Received: from yale-venus.ARPA by KL.SRI.COM with TCP; Sun 9 Aug 87 13:51:17-PDT
Date:  9 AUG 1987 16:45:38 EST
From: <LEICHTER-JERRY@YALE.ARPA>
To: TOLLIVER%ORN.MFENET@nmfecc.arpa
cc: INFO-VAX@KL.SRI.COM
Subject:  Re: Problems defining MAIL$EDIT to be CALLABLE_TPU
Reply-To: <LEICHTER-JERRY@YALE.ARPA>

    ...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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