IBM MAINFRAME HELP & SUPPORT FORUMS

kalpana · Joined: 19 Nov 2004 Posts: 25 Location: Banglore

Hi all,
Could any one please let me know the answers for the below assembler questions

1) How to pass parameters to the sub program and how we will recieve it back? ( I need this with sample code)

2) How to access array elements in assembler?

3) what is the significane of NOP ( No Operation)

4) How you can call a sub program dynamicaly

Garry Carroll · Joined: 08 May 2006 Posts: 166 Location: Dublin, Ireland

1) Parameters are passed, by convention, using register 1 (R1). R1 is set to the address of the first parameter. The last parameter in the parameter list has the high-order bit set 'on'.

Thus:
Code:

L R1,=A(FIRST)
ST R1,PARM1
L R1,=A(SECOND)
ST R1,PARM2
L R1,=A(THIRD)
ST R1,PARM3
OI PARM3,X'80'
L R1,=A(PARMLIST)

CALL NEXTPROG

PARMLIST DS 0F
PARM1 DS F
PARM2 DS F
PARM3 DS F

NEXTPROG will have code to retrieve these parms - e.g.

Code:

LM R2,R4,0(R1)
LA R4,0(R4) * lose high-order bit

Any changes made are visible to the calling program at the addresses specified.

2) A number of ways. For an array with multiple fields per array entry, provide a DSECT which describes those fields. Using registers, caclulate the offset to the array entry to require and align the DSECT before using the field names.

3) NOP is a "no operation". Its significance depends on the program context. It might be modified "on the fly" to a branch, though that's frowned upon these days.

4) If you don't link the program as static at linkedit time it should be called dynamically.

Regards,
Garry.

kalpana · Joined: 19 Nov 2004 Posts: 25 Location: Banglore

Thanks alot for ur quick response.