I'm contemplating my first HLASM function to be called from XPLINK C++. (I'm quite experienced with HLASM in general, including old-fashioned OS/360 linkage.) It's not going to be a very complex function: three input parameters, minimal processing and a return code.
Gosh, it seems like the documentation is fragmented here and there! There seems to be a little bit in LE Vendor Interfaces, a little bit in the LE P/G, a little bit in LE Writing ILC, a little bit in the XLC P/G, . The only example I find is tiny and uses a couple of obscure features. If this is actually all documented in one place somewhere, with a couple of good examples, please just point me there. The arguments come in to the HLASM in R1-R3. If the C++ says FOO(17) then R1 will contain 17 and if the C++ says BAR(&SOJACK) then R1 will contain the address of SOJACK? I put the return code in R3, like I used to put it in R15? R4-R7 I guess I need to preserve? In my case I can live without touching them. But if I needed to alter them, I have to save them? Where? Anywhere I want in my writeable storage? There is no saving "convention" like the old STM 14,12,12(13)? R7 I need to preserve because R7 is the return address, like R14 in the old days. EDCXEPLG will handle return linkage just so long as R4-R7 and R12 are good? Where is the DSA? Where is my writeable storage? My "work area"? I guess I need to preserve R12? So R13 through R3 and R8 through R11 are mine to play with without saving and restoring, other than that the parms come in in R1-R3 and the return code needs to end up in R3? Thanks, Charles
