[Info-vax] Non-portable code

[Marc Van Dyck]

G'd evening to all...

I have a program on my systems, that was written in the VAX ages,
and that I use to display which version of layered products, tools, 
etc,
are installed. It simply extracts from the image headers the version
info that has been put there by the linker, with the IDENT clause of
the link options file.

Here is an extract of the code that does it (Pascal) :

RESET ( f ) ;
buffer := f^ ;
CLOSE ( f ) ;

addr := IADDRESS (buffer) +
        buffer[EIHD$L_IMGIDOFF+1]::$UBYTE +
        EIHI$T_IMGID ;
image_id.LENGTH := 0 ;

LIB$MOVC3 ( word_integer_length := 1 ,
            source := %IMMED addr ,
            destination := image_id.LENGTH ) ;
addr := addr + 1 ;
STR$COPY_R ( destination_string := image_id.BODY ,
             word_integer_source_length := image_id.LENGTH ,
             source_string_address := %IMMED addr ) ;

(Assuming that f is an executable image file and image_id the place for
the info that I want to obtain)

EIHD$L_IMGIDOFF and EIHI$T_IMGID are declared as [EXTERNAL,VALUE]
variables and resolved at link time by inserting a .STB file (don't
remember which one, I'm at home here) in the link options file.

This works perfectly well on VAX and Alpha. On Itanium, it compiles
but either gives false results, or even ACCVIOes (I suppose that it
happens when what I read in buffer[EIHD$L_IMGIDOFF+1] is absurdly 
high).

So, a few questions :

For Integrity images, is the method I used above still valid - but with
wrong offsets - or am I completely screwed up ? If positive, what are
the offsets that I should use ? If not, how should I do ? Is it
documented somewhere ?

If the offsets EIHD$L_IMGIDOFF and EIHI$T_IMGID are wrong on Integrity,
why is it possible that the program compiled and linked with no problem
at all ? I would have expected that those either have the correct 
value,
or do not exist at all, in which case the link would have failed. Where
am I wrong ?

If I need to have code differences between the VAX/AXP and the I64
version, do I need to have two separate source files, or does Pascal
provide some way of conditional compiling ?

Many thanks in advance for your help. This is the first time I
encouter code which is not source-compatible between the 3 VMS
hardware architectures...

-- 
Marc Van Dyck