Take a closer look. "@PRINTF4", rather than "printf", is being called by the
CALLPRTF assembler module. ("Figure 2. Calling an intermediate C function from
Assembler OS linkage")
@PRINTF4 (actual name _printf4) is defined later on that page:
/* this example demonstrates C/Assembler ILC */
/* part 3 of 3 (other files are CCNGCA2, CCNGCA4) */
/*******************************************************\
* This routine is an interface between assembler code *
* and the C/C++ library function printf(). *
* OS linkage will not tolerate C-style variable length *
* parameter lists, so this routine is specific to a *
* formatting string and a single 4-byte substitution *
* parameter. It's specified as an int here. *
* This object wil be named @PRINTF4. *
/*******************************************************/
#pragma linkage(_printf4,OS) /*function will be called from assembler*/
#include <stdio.h>
#pragma map(_printf4,“@PRINTF4”)
int _printf4(char *str,int i) {
return printf(str,i); /* call runtime library function */
}
Because of the linkage pragma that specifies "OS" I imagine that, although the
C code is defined as "pass by value", the OS linkage overrides it to be passed
by reference. Just a guess; I don't have a C compiler.
________________________________
From: IBM Mainframe Discussion List <[email protected]> on behalf of
Paul Gilmartin <[email protected]>
Sent: Thursday, March 30, 2023 5:23 PM
To: [email protected] <[email protected]>
Subject: Re: ASM call by value
On Thu, 30 Mar 2023 23:39:30 +0200, Bernd Oppolzer wrote:
>
>"call by value" in my understanding means, that values are passed, not
>addressed.
>With the mainframe (or z/OS and CMS) linkage convention, this means,
>that values
>and not addresses are in the reg1 parameter list.
>
What happens if there are more value parameters than the total capacity of
registers?
(But do I misunderstand? Is the "reg1 parameter list" not actual registers but
the
storage addressed by GR1 in the CALL macrlo? If so, it's no practical limit.)
>see above. Because the values entered into the reg1 list "by value" can
>be negative integers
>(or other types, which need more that 4 bytes), the VL convention cannot
>be used by C callers
>
Hmmm. In
<https://www.ibm.com/docs/en/zos/2.5.0?topic=programs-calling-c-code-from-assembler-c-example>
I see:
EDCPRLG
LA 1,ADDR_BLK parameter address block in r1
L 15,=V(@PRINTF4) address of routine
BALR 14,15 call @PRINTF4
EDCEPIL
ADDR_BLK DC A(FMTSTR) parameter address block with..
DC A(X'80000000'+INTVAL) ..high bit on the last address
* ...
INTVAL DC F'222' The integer value displayed
*
Isn't the "X'80000000'" setting the VL bit?
(I note that's a CD not an EQU. But the reg1 PL contains an address not a
value.)
Again, either the caller or the called routine could be able
to convert addresses to values.
--
gil
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