Getting into supervisor mode and other hard things in C, is easy.

Some functions in z/OS need a user to be in a privileged state such as key zero or supervisor state. Writing the code in assembler has been pretty easy, but writing it in a C program has been hard.

For example you could write a function in assembler, and call it. This has the cross language challenges.

I recently found an easy way – just reuse some code from Zowe. This is open source, so you need to follow the license

This program and the accompanying materials are made available under the terms of the Eclipse Public License v2.0 which accompanies this distribution, and is available at https://www.eclipse.org/legal/epl-v20.html

SPDX-License-Identifier: EPL-2.0

Copyright Contributors to the Zowe Project.

The code uses __asm() Inline assembly statements (IBM extension).

The functions are

• ddnameExists
• wtoMessage
• wtoPrintf3
• atomicIncrement compare and swap
• testauth
• extractPSW
• supervisorMode or back to problem state
• setKey
• getExternalSecurityManager
• getCVT
• getATCVT
• getIEACSTBL
• getCVTPrefix
• getECVT
• getTCB
• getSTCB
• getOTCB
• getASCB
• getASXB
• getASSB
• getJSAB
• getCurrentACEE
• getFirstChildTCB
• getParentTCB
• getNextSiblingTCB
• resolveSymbolBySyscall Input: A symbol starting with & and not ending with .
• resolveSymbol Input: A symbol starting with & and not ending with .
• lots of saf functions see here
• loadByName
• getDSAB Data Set Association Block
• isCallerLocked
• isCallerCrossMemory

Some of these need to be APF protected, so although it is easy to use the above code, you may still need to get the load library APF authorised, and the code approved.

For example

Get into supervisor state

The code here.

int supervisorMode(int enable){
// Use MODESET macro for requests
  int currentPSW = extractPSW();
  if (enable){
    if (currentPSW & PROBLEM_STATE){
      __asm(ASM_PREFIX
            " MODESET MODE=SUP \n"
            :
            :
            :"r0","r1","r15");
      return TRUE;
    } else{
      return FALSE;  /* do nothing, tell caller no restore needed */
    }
  } else{
    if (currentPSW & PROBLEM_STATE){
      return TRUE;   /* do nothing, tell user was in problem state */
    } else{
      __asm(ASM_PREFIX
            " MODESET MODE=PROB \n"
            :
            :
            :"r0","r1","r15");
      return FALSE;
    }
  }
}

To compile it I used

// SET LOADLIB=COLIN.LOAD 
//DOCLG       EXEC   PROC=EDCCB,INFILE='ADCD.C.SOURCE(C)', 
//            CPARM='OPTF(DD:COPTS)' 
//*           CPARM='LIST,SSCOMM,SOURCE,LANGLVL(EXTENDED)' 
//COMPILE.ASMLIB DD  DISP=SHR,DSN=SYS1.MACLIB 
//COMPILE.COPTS DD * 
LIST,SOURCE 
aggregate(offsethex) xref 
SEARCH(//'ADCD.C.H',//'SYS1.SIEAHDR.H') 
TEST 
ASM 
RENT ILP32        LO 
OE 
NOMARGINS EXPMAC   SHOWINC XREF 
LANGLVL(EXTENDED) sscom dll 
DEFINE(_ALL_SOURCE) 
DEBUG 
/* 
...

You need to specify

• //COMPILE.ASMLIB for the the assembler macro libraries.
• and the compiler option ASM which enables inlined assembly code inside C/C++ programs.

I was all so easy, once I had been told about it.