Re: S/3xx (was Market pressures for more reliable software)

Re: S/3xx (was Market pressures for more reliable software)

[robin]

"Shmuel (Seymour J.) Metz" <nospam@acm.org> writes: > 
> 
> robin wrote:
> 
> > No. It used relative addressing, and base-relative addressing.
> > (strictly speaking, it used base-displacement-indexed addressing.)
> > The assembler allowed "absolute" addresses to be specified,
> > which had to be filled in by the loader.
> 
> You're confusing two different things.

I'm not confusing anything.

> The S/360 used absolute addresses,

There was only one case when the S/3xx used absolute addressing.
That was when the base register field of an instruction was zero.
The displacement was then effectively the absolute address (in the
range 0-4095).

Remaining addressing mode was base-displacement-indexed addressing,
except for SS instructions, which used base-displacement addressing.

> but they were not present in
> instructions. At least, it did until prefixing came along.
> As to assembler language, it was relocatable addresses
> that had to be adjusted by the loader;

Relocatable addresses are not "adjusted by the loader".
This is done automatically via the base register(s).

> if the program specified
> an absolute address, then the loader did not have
> to adjust it.

When an address constant [A(xxx)] is specified, the loader has to
supply the relevant actual address.  The assembler can only provide
a relative address.

> > Any program can be loaded anywhere in memory.
> > Programs can be made dynamically relocatable, but only with some effort.

> --
> Shmuel (Seymour J.) Metz

Re: S/3xx (was Market pressures for more reliable software)

[Shmuel (Seymour J.) Metz]

In <KYG_6.10158$e5.28393@newsfeeds.bigpond.com>, on 06/28/2001
   at 02:14 PM, robin <robin_v@bigpond.nospam.com> said:

>I'm not confusing anything.

You were and you still are. If you conult Princciples of Operation you
will note that it never refers to the displacement as an address, but
instead talks about how the processor *generates* an address from the
displacement.

>Relocatable addresses are not "adjusted by the loader". This is done
>automatically via the base register(s).

When did you drop out of the communist party? What? You claim you
never belonged? Well, I never said that the loader adjusts
displacements. As to relocatoable addresses, see p. 98 of SY28-6659-7,
which states "Changes the values of address constants in the loaded
program from relative addresses to absolute addresses."

>When an address constant [A(xxx)] is specified, the loader has to
>supply the relevant actual address.  The assembler can only provide
>a relative address.

When I specify an address constant of A(16), what action does the
loader need to take to adjust it? The assembler documentation clearly
spells out the difference between relocatable and nonrelocatable
values.

-- 
-----------------------------------------------------------
     Shmuel (Seymour J.) Metz, SysProg and JOAT
     Atid/2
     Team OS/2
     Team PL/I

Any unsolicited commercial junk E-mail will be subject to legal
action.  I reserve the right to publicly post or ridicule any
abusive E-mail.

I mangled my E-mail address to foil automated spammers; reply to
domain acm dot org user shmuel to contact me.  Do not reply to
spamtrap@library.lspace.org
-----------------------------------------------------------