From:	SMTP%"ALPHA-IDS%WKUVX1.bitnet@ULKYVM.LOUISVILLE.EDU"  7-OCT-1993 16:07:46.45
To:	EVERHART
CC:	
Subj:	RE: SYS$IMGACT in VMS AXP

X-ListName: OpenVMS AXP (Alpha) Internals <ALPHA-IDS@WKUVX1.BITNET>
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Date: Thu, 7 Oct 93 12:45:55 PDT
From: <mahan@TGV.COM>
Reply-To: ALPHA-IDS%WKUVX1.bitnet@ULKYVM.LOUISVILLE.EDU
Message-ID: <931007124555.69e00130@TGV.COM>
Subject: RE: SYS$IMGACT in VMS AXP
To: arne@kopc.hhs.dk, <alpha-ids%wkuvx1.bitnet%cunyvm.cuny.edu@TGV.COM>
X-ST-Vmsmail-To: ST%"ARNE@kopc.hhs.dk"

#
# I am having some problems getting SYS$IMGACT to work under VMS AXP.
#
# Yes - I know SYS$IMGACT is unsupported and that I should be a nice
# boy and use LIB$FIND_IMAGE_SYMBOL, but I like some of the features
# of SYS$IMGACT !
#
# My questions are:
#
#   1)  Is HDRBUF still pointing to a 512 byte buffer ?
#
#       (I know that the format has changed, symbolic names has
#        been prefixed with E's and some W-fields has become
#        L-fields)
#

According to the Alpha listings it is still 512 bytes.  However, during our
port to the Alpha, it seems to me that it could be larger.  On the vax we
store stuff at the first of the image and did a 512 byte read to get past
the header.  On the Alpha, we had to do 2 512 byte reads to get past the
header (and what ever else was there).


#
#   2)  Is INADR and RETADR pointing to a 2-L-array or a 2-Q-array ?
#

Again, according to the listings it is still a 2 longword array.

#
#   3)  Is it possible to call a transfer-address found in the image-header
#       in MACRO32 ?
#
#       (a transfer-addresses is Q on VMS AXP, but the MACRO-compiler seems
#        still to use L addresses)
#

Well there really are *no* transfer addresses on the Alpha.  Instead, that value
should be a pointer to the procedure descriptor.  It is still possible to call,
but not the way you do it on the VAX.  Here is a piece of code that shows the
layout of the Procedure descriptor:

        .PROCEDURE_DESCRIPTOR   'NAME', _'NAME'         ;Define Name
        .WORD                   ^X1808                  ;Flags, Kind=NULL
        .WORD                   0
        .WORD                   26                      ;Entry_RA
        .WORD                   0                       ;No signature
        .ADDRESS                _'NAME'                 ;Code Address


Hope this helps.

Patrick L. Mahan

--- TGV Window Washer ------------------------------- Mahan@TGV.COM ---------

Waking a person unnecessarily should not be considered  - Lazarus Long
a capital crime.  For a first offense, that is            From the Notebooks of
                                                          Lazarus Long