[llvm] [SystemZ][z/OS] Emit CELQMAIN for a module defining main (PR #226710)

[MMS IT GmbH via llvm-commits]

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@@ -289,6 +294,53 @@ void SystemZXPLINKAsmPrinter::emitEndOfAsmFile(Module &M) {
   }
 }
 
+// Emit CELQMAIN in RENT format (see z/OS Language Environment Vendor
+// Interfaces, "Program initialization and termination for AMODE 64
+// applications"):
+//   +0   X'04000001'
+//   +8   AD(main entry point)
+//   +10  AD(CELQINPL)
+//   +18  A(0) / Q(environment); emitted as 8 byte R-con to main, which the
+//        binder resolves to the offset of the ADA of main (fits into 4 bytes)
+// followed by a reference to the bootstrap routine CELQBST. CELQSTRT only has
+// a weak reference to CELQBST, so without it autocall would not include it.
+void SystemZXPLINKAsmPrinter::emitCELQMAIN(const Function &MainFn) {
+  MCSymbol *MainSym = getSymbol(&MainFn);
+  auto ExternalOSSymbol = [&](StringRef Name) {
+    MCSymbol *Sym = OutContext.getOrCreateSymbol(Name);
+    OutStreamer->emitSymbolAttribute(Sym, MCSA_OSLinkage);
+    OutStreamer->emitSymbolAttribute(Sym, MCSA_Global);
+    return Sym;
+  };
+  MCSymbol *CELQINPL = ExternalOSSymbol("CELQINPL");
+  MCSymbol *CELQBST = ExternalOSSymbol("CELQBST");
+
+  OutStreamer->pushSection();
+  OutStreamer->switchSection(getObjFileLowering().getTextSection());
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mms-it-ch wrote:

Moved the emission of CELQMAIN to emitStartOfAsmFile(), next to the PPA2, while the text section is still open (5a538af43). Added zos-celqmain-debug.ll with debug info and -generate-arange-section, which hit the "Section already ended" assertion before.

_🤖 Addressed by [Claude Code](https://claude.com/claude-code)_

https://github.com/llvm/llvm-project/pull/226710