Sorry ... in some places: replace "caller" by "called prog" ...
Am 27.03.2023 um 08:49 schrieb Bernd Oppolzer:
Sorry that I post to the original question;
that's because most of the answers so far missed the point.
Call by value means that a value is passed to the caller;
call by reference means that a reference (technically: an address) is
passed to the caller.
In ASSEMBLER:
CALL SUBPROG,(A,B,C),VL
sends address constants of fields A, B and C to the caller (via reg1
address list),
so that is always call by reference.
You can instead send an integer constant to the caller using CALL or a
register:
CALL SUBPROG,(1024,(R3))
with the integer constant, this sure is call by value, but you are
limited to integer arguments.
With the register argument, it depends on what is contained in the
register;
if it is an address, you have call by reference again.
The only real "call by value" I can see here is the case where an
integer constant is part
of the reg1 parameter list (the 1024 constant above); and this is what
C technically does
in the "call by value" case. If C passes larger values "call by
value", it copies them in the
reg1 parameter list. This CANNOT BE DONE using the CALL macro. And
this would be
the correct answer to the original question.
HTH,
kind regards
Bernd
Am 26.03.2023 um 23:35 schrieb Frank Swarbrick:
Can the MVS CALL macro be used to call a C function with "value"
parameters (rather than reference parameters)?
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