On Mon, 23 Aug 2021 11:54:19 +0000, Seymour J Metz wrote:
[Re: <https://en.wikipedia.org/wiki/Position-independent_code>]
>How would you handl calls to sepaerately compiled subroutines without RLD? How
>would you write PIC that called external subroutines?
>
If statically linked:
LA R15,EPTR
AL R15,EPTR
BALR R14,R15 R15 is available as a code base.
...
* Linker will resolve RLDs -- pairing makes the value absolute.
EPTR DC A(SUBR-*) This value is position-independent.
If dynamically loaded, read the module to any location with a
channel program. RLDs were resolved by linker.
Place its address in R15
BALR R14,R15 R15 is available as a code base.
Some OS (DOS 360?) (CMS?) had a convention of "transient"
modules, loadable anywhere, either PIC or containing prologues
to modify addresses.
I recall FORTRAN II for IBM 700/7000. Each subroutine contained
a prologue to replace addresses of formal parameters with addresses
of actual parameters. Self-modifying; horribly NORENT.
>________________________________________
>From: Paul Gilmartin
>Sent: Monday, August 23, 2021 5:29 AM
>
>On Sun, 22 Aug 2021 17:04:20 -0700, Charles Mills wrote:
>
>>Not what you asked, but can one MVCL a load module ...
>>Of course in some case one might know that the
>>load module in question was a table e.g. that had no RLDs.
>>
>https:[...]
>
>I was once modifying a [FOSS] Pascal compiler ...
-- gil
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