[Info-vax] Non-portable code

[Jan-Erik Söderholm]

Marc Van Dyck wrote:
> Marc Van Dyck formulated the question :
>> 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...
> 
> OK gentlemen, thank you very much to all for your help. We have been
> able to transform the C code that John Reagan posted here into a
> function that my Pascal program can call. It works very well,
> so my problem is solved.
> 

Just so it's fully understood...

Why not simply use ANALYZE/IMAGE ?
What extra does your Pascal program give ?