Argument list examples
All examples shown are for non-extended-mode enabled routines.
Example 1A: call Suba(l1,d,l2)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
R1 0 | l1... | P1
---------------------
FP0 4 | du... | P2
---------------------
8 | dl... | P3
---------------------
STACK 12 | l2 | P4
---------------------Note that the compiler does not initialize the related argument slots in the argument area of the stack, although they are still allocated in case the callee needs them. Only one word is used in the corresponding argument slot in the argument area.
Example 1B: call Suba(d,l1,l2)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
FP0 0 | du... | P1
---------------------
4 | dl... | P2
---------------------
GPR3 8 | l1... | P3
---------------------
STACK 12 | l2 | P4
---------------------Example 1C: call Suba(&d,l1,&l2,&l3)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
GPR1 0 | address of d | P1
---------------------
GPR2 4 | l1 | P2
---------------------
GPR3 8 | address of l2 | P3
---------------------
STACK 12 | address of l3 | P4
---------------------The next examples illustrate the passing of argument areas by reference parameters.
Example 2: call Suba(e,l)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
FP0/FP2 0 | euu... | P1
---------------------
4 | eul... | P2
---------------------
8 | elu... | P3
---------------------
12 | ell... | P4
---------------------
STACK 16 | l | P5
---------------------Example 3: call Suba(d1,d2,l)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
FP0 0 | d1u... | P1
---------------------
4 | d1l... | P2
---------------------
STACK 8 | d2 | P3
| |
12 | | P4
---------------------
STACK 16 | l | P5
---------------------Example 4: call Suba(l1,l2,d1,d2,l3)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
R1 0 | l1... | P1
---------------------
R2 4 | l2... | P2
---------------------
FP0 8 | d1u... | P3
---------------------
12 | d1l... | P4
---------------------
STACK 16 | d2 | P5
| |
20 | | P6
---------------------
STACK 24 | l3 | P7
---------------------Example 5: call Suba(s,l1,e,l2)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
-----+----+----------
R1 0 |\\\\|\\\\|s... | P1
---------------------
R2 4 | l1... | P2
---------------------
FP0/FP2 8 | euu... | P3
---------------------
12 | eul... | P4
---------------------
16 | elu... | P5
---------------------
20 | ell... | P6
---------------------
STACK 24 | l2 | P7
---------------------Example 6: call Subc (s1-l1-d1,l2,f2,d2)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
----------+----------
R1 0 | s1 |////|////| <--- left justified or as
--------------------- dictated by struc mapping
R2 4 | l1... | P2 rules in language
---------------------
R3 8 | d1u... | P3
---------------------
STACK 12 | d1l | P4
---------------------
STACK 16 | l2 | P5
---------------------
STACK 20 | f2 | P6
---------------------
STACK 24 | d2 | P8
| |
38 | | P9
---------------------Example 7: call Subb(l1, s1, l2, d1, f1, c1,s2,s3-l3-f2)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
R1 0 | l1... | P1
-----+----+----------
R2 4 |\\\\|\\\\|s1... | P2
---------------------
R3 8 | l2... | P3
---------------------
STACK 12 | d1 | P4
16 | | P5
---------------------
STACK 20 | f1 | P6
-----+----+----+-----
STACK 24 |\\\\|\\\\|\\\\| c1 |
---------------------
STACK 28 |\\\\|\\\\| s2 |
---------------+-----
STACK 32 | s3 |////|////| <--- left justified or as dictated
--------------------- by struct mapping rules in
STACK 36 | l3 | P10 language
--------------------|
STACK 40 | f2 | P11
--------------------- Note that you can not pass single precision floating point to a language like C++, which, upon call, promotes all single precision value arguments to double precision, and get it to work reliably. The first floating argument might happen to work because it is in a register.
Example 8: call Suba(f1,1,l2,f2)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
FP0 0 | f1... | P1
---------------------
GPR2 4 | l1... | P2
---------------------
GPR3 8 | l2... | P3
---------------------
STACK 12 | f2 | P4
---------------------Note that C++ on 390 always performs a promote of short floating values to long floating point. Thus, in some cases, C++ on 390 will not actually work as described above.
Example 9: call Suba(v,l)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
VR24 0 | vuu... | P1
---------------------
4 | vul... | P2
---------------------
8 | vlu... | P3
---------------------
12 | vll... | P4
---------------------
STACK 16 | l... | P5
---------------------
Example 10: call Suba(l,d,v1,v2)
STORAGE MAPPING OF
WILL BE PASSED IN: ARG AREA ON THE STACK
---------------------
R1 0 | l... | P1
---------------------
FP0 4 | du... | P2
---------------------
8 | dl... | P3
---------------------
VR24 12 | vluu... | P5
---------------------
16 | vlu1... | P6
---------------------
20 | vllu... | P7
---------------------
24 | vlll... | P8
---------------------
VR25 28 | v2uu... | P9
---------------------
32 | v2u1... | P10
---------------------
36 | v21u... | P11
---------------------
40 | v2l1... | P12
---------------------
A vector argument is full-word-aligned
and occupies 16 bytes in the argument list.