CEETHLOC — stub for trigger load on XPLINK call by name

The function of the CEETHLOC stub (Figure 1) is to interface to the CEEPHTLC (XPLINK Trigger Load on Call) routine on behalf of an unresolved "by-name" function call, which will load the DLL and then invoke the function. This stub is directly referenced from the compilation unit's generated code, and is link-edited in the same program object as the compilation unit. The compiler-generated code will locate the function descriptor, load registers 5 and 6 from the start of the function descriptor, and branch to the stub address in register 6. Once inside the stub, register 7 contains the return address and register 5 contains the 'function_id' identifying this imported function (from the first word of the descriptor). Register 6 is used as a work register to load and branch to the entry point of the CEEPHTLC function.

Figure 1. CEETLOC stub for trigger load on XPLINK call by name

*/********************************************************************/
*/*                                                                  */
*/*    CEETHLOC - Language Environment                               */
*/*               "trigger load on XPLINK; call by name" stub        */
*/*                                                                  */
*/*    This stub contains one entry point                            */
*/*    + 0 for XPLINK linkage                                        */
*/*                                                                  */
*/********************************************************************/
CEETLOCE CSECT
CEETLOCE RMODE ANY
CEETLOCE AMODE ANY
*
         DS    0D                        Doubleword aligned...
         DC XL7'00C300C500C500'          eyecatcher text ".C.E.E."
         DC XL1'F4'                      eyecatcher marker "4"
*
         ENTRY CEETHLOC
CEETHLOC XATTR LINKAGE(XPLINK)
CEETHLOC DS    0D                        Real entry pt of stub
         L     6,CEECAACELV-CEECAA(,12)
         L     6,CEECELVPHTLC-CEECELV(,6)
         BR    6
*
         CEEXCELV
         CEEXCAA
         END   CEETLOCE

Register Usage:
R4

DSA address

R5

Identifier that represents the XPLINK function that is in the target DLL

R6

Entry point address of CEETHLOC

R7

Return address to caller

R12

CAA address

Compiler-generated code sample:

   LM    r5,r6,dd+0(envreg)       load environment & function addresses
*                                  ... from function descriptor
   BASR  r7,r6                    call the function
   DC    X'4700'
   DC    Y(signed offset/8 to entry point marker)