Re: Re: Where do I start?

On 5/26/2010 11:52 PM, Ron Hudson wrote:
> So, the base register is the one that is wearing the "base register hat"
> at any given moment.
> You put the hat on a given register with the "using" instruction and
> take the hat away with
> the "drop" instruction?
>
> What happens if there are two using instructions that promote different
> registers without
> a drop?

When you have overlapping or identical ranges, the assembler is 
supposed to use the one with the lowest displacement. As long as 
both registers have the correct contents, no harm is done. 
Assemblers after IFOX00 (IEV90, ASMA90) will flag overlaps with 
a level 4 warning (may be turned off).

> Between these two lines is the program without a base register?

No; the assembler uses one or the other.

> Would I even need to branch to a specific address in memory?
> Or all branches relative to the base address?
> Shared Libraries?

The arrangement of base/displacement addressing allows automatic 
relocation of your code, so you don't need to know the program's 
address, because the branches are relative. Later on you'll run 
into V and A constants that allow you to address subroutines and 
data by address, rather than displacement.

>     Also note that when TSO gives an error message with a ?, hitting
>     enter will produce one or more additional messages.

I'm really out of it tonight - that's two wrong tries. As 
mentioned by Rick, if you see a plus sign, it indicates 
additional data, obtained by typing ? and Enter.

Gerhard Postpischil
Bradford, VT


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