To: J3                                                     11-152r1
From: Jim Xia/Bill Long
Subject: Interop: Constraints on descriptors and usage
Date: 2011 February 18
References: N1838,11-126, 11-127, 11-128, 11-133, 11-134,
	    11-143r1, 11-144r2


DISCUSSION

In view of the changes in paper 11-144r2, several of the underlying
assumptions in papers on related topics are changed, and the issues
raised there might be automatically resolved.  This paper summarizes
the resulting status of papers 11-126, 11-127, 11-128, 11-133, 11-134,
and 11-143r1.

11-126:
-------

Updating or copying a C descriptor is disallowed by the following
edits in 11-144r2:

"
5.2.7 Use of C descriptors

A C descriptor shall not be initialized, updated or copied other than
by calling the functions specified here. ..."


11-127:
-------

The "redundant restriction" between 5.2.6p2 and 5.2.7p1 is removed by
144r2 (which replaces 5.2.7 from N1838).

Issues raised in 5.2.7 are resolved because 11-144r2 disallows
modification of a C descriptor after its initialization except to use
functions provided in 5.2.6.


11-128:
-------

The proposed edits are included in 11-144r2.


11-133:
-------

Paper 11-133 proposed changes to the CFI_associate function. That
function was deleted by 11-144r2.


11-134:
-------

The issues raised appear to be covered by 11-144r2.


11-143r1:
---------

a.) assumed-type array issues are resolved

    1.) assumed-shape array is always passed by C descriptor, which
	contains its actual type and elem_len, etc.  So there is no
	issue to index this array in C program.

    2.) explicit-shape array with assumed type is disallowed, and
        further the assumed-size array is required to be of rank 1
        (11-124r3)

    3.) pointer and allocatable are disallowed (11-111r2)

    Summary: For TYPE(*) only assumed-size array (rank 1) can be
    passed using address.  See updated 2.1.

b.) alignment issue in "CASTING" example of A1.3

    option 1: add comment in A1.3 to say "assume the parameter block
           is aligned for casting to integer type."

    option 2: remain silent because the correct alignment is assumed.


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