[Info-vax] Non-portable code

[VAXman- at SendSpamHere.ORG]

In article <mn.2d1b7da1fb0d0bdb.104627 at brutele.be>, Marc Van Dyck <marc.vandyck at brutele.be> writes:
>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 ?

This will NOT work on IA64.  You need too study ELF.


>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 ?

They're not wrong.  The image format was NOT devised by DEC/Compaq/HP and
VMS engineering.  The chose to go with ELF.  Check $ELFDEF in STARLET.MLB


>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 ?

Pascal specific questions are best left to John Reagan.  I've done 
what you are seeking to do in Macro32 with a common source file.
 

>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...

You haven't looked very hard! :)

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