Page of GC20-1801-10 As Updated April 1, 1981 by TNL GN25-0837 Updating the Loader Program Updating the Loader Program
The loader (DMKLDOOE) is a service program that loads a CP; eMS; or RSCS nucleus, and produces a load map. The loader loads the object modules
(text files) supplied with it, resolves CCW addresses, and resolves
address constants.
If an overlay error occurs while the loader is executing, define a
larger virtual machine and reload the system.
The loader is distributed with the following default I/O addresses: Console=009 Printer=OOE If there is no printer at address OOE, the load map is printed at the
first printer that causes an interrupt (not-ready to ready sequence).
Note: The loader does not support display mode consoles. If an IPL is
attempted, wait state code 'FFF' is entered if the printer address is
not OOE. To circumvent this occurrence, reconfigure the console to
printer-keyboard mode or use the following procedure to correct the
printer address. You can override these addresses by placing a control card between
the last card of the loader and the first card of the text decks. The
format of the control card is: Colu1!.ll 1 2-4 5
6-13 14 15-22
23-72
contents 12-2-9-multipunch (X'02') DEV blank
PRNT=cuu (cuu is the printer address)
blank or comma TYPW=cuu(cuu is the console address)
blank
The other loader control statements are the same as the loader
control statements described with the CMS LOAD command in the VM/370 Command KacrQ Reference.
The loader is self-relocating, that is, it is initially loaded at
address 2000 (hexadecimal); it then relocates itself at the top of
storage. (For example, if the size of the loader is 10K, and the real
storage size of the CPU is 512K, the loader occupies the area of storage
between 502K and 512K.) As the loader needs free storage to perform its
operations, it extends downward through storage.
The object modules being loaded must not overlay either the loader or
any address between 0 and 100 (hexadecimal). The object modules are
loaded into storage in a positive direction (that is, upward through
storage). Before the loader actually loads an object module, it checks
that the module does not overlay the loader's free storage. If an object
module would overlay the loader, the loader terminates. You must close
the printer to get the load map printed. The last line of the load map
indicates the overlay area, if there was one. Part 5. Updating VM/370 371

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If the loader terminates the operation, a wait condition is indicated
in the instruction counter. If the instruction counter contains X'gggggg', indicating an SVC wait state, the interruption code (the
third and fourth bytes of the supervisor old PSW) indicate the error
condition. For a detailed explanation of the error conditions and
interruption codes, see VM/370 System Messages.
The Load Map The load map (the output of the loader) indicates: • The size of each object module and the address where it is loaded.
For example:
DMKMCH AT 00E68 MODULE SIZE IS OOOCOO • The end of the resident nucleus with the message:
*** ***
END OF VM/370 RESIDENT NUCLEUS *** ***
The CP modules that precede this message in the load map are not
pageable; the CP modules that follow this message are pageable. • When a Set Page Boundary (SPB) card has been inserted. If an object
module cannot fit on the same page as the object module(s) loaded
before it, the loader inserts an SPB card to force the modules to be
loaded at a page boundary. This procedure ensures that object modules
do not cross page boundaries. • Two external names may be listed as undefined on the load map. If
the virtual=real option is not specified, the external name DMKSLC is
listed as undefined. If a 3704/3705 control program entry is not
defined in the system name table (via the NAMENCP macro), the
DMKRNTBL external name is undefined.
Generating a New Loader
The loader service program, in its
LOADER. Whenever you assemble a new
the resulting text file to a loader
at address OOD and a virtual reader
generating a new loader is:
executable form, has a filetype of
copy of DMKLDOOE, you must convert
file. If there is a virtual punch
at address OOC, the procedure for
372 IBM VM/370 Planning and System Generation Guide