[llvm] [SystemZ][z/OS] This change adds support for the PPA2 section in zOS (PR #68926)

[Ulrich Weigand via llvm-commits]

================
@@ -1296,6 +1372,124 @@ void SystemZAsmPrinter::emitPPA1(MCSymbol *FnEndSym) {
                                       4);
 }
 
+void SystemZAsmPrinter::emitStartOfAsmFile(Module &M) {
+  if (TM.getTargetTriple().isOSzOS())
+    emitPPA2(M);
+  AsmPrinter::emitStartOfAsmFile(M);
+}
+
+void SystemZAsmPrinter::emitPPA2(Module &M) {
+  OutStreamer->pushSection();
+  OutStreamer->switchSection(getObjFileLowering().getPPA2Section());
+  MCContext &OutContext = OutStreamer->getContext();
+  // Make CELQSTRT symbol.
+  const char *StartSymbolName = "CELQSTRT";
+  MCSymbol *CELQSTRT = OutContext.getOrCreateSymbol(StartSymbolName);
+
+  // Create symbol and assign to class field for use in PPA1.
+  PPA2Sym = OutContext.createTempSymbol("PPA2", false);
+  MCSymbol *DateVersionSym = OutContext.createTempSymbol("DVS", false);
+
+  std::time_t Time = TranslationTime;
+  SmallString<15> CompilationTime; // 14 + null
+  raw_svector_ostream O(CompilationTime);
+  O << formatv("{0:%Y%m%d%H%M%S}", llvm::sys::toUtcTime(Time));
+
+  uint32_t ProductVersion = getProductVersion(M),
+           ProductRelease = getProductRelease(M),
+           ProductPatch = getProductPatch(M);
+
+  SmallString<7> Version; // 6 + null
+  raw_svector_ostream ostr(Version);
+  ostr << formatv("{0,0-2:d}{1,0-2:d}{2,0-2:d}", ProductVersion, ProductRelease,
+                  ProductPatch);
+
+  // Drop 0 during conversion.
+  SmallString<sizeof(CompilationTime) - 1> CompilationTimeStr;
+  SmallString<sizeof(Version) - 1> VersionStr;
+
+  ConverterEBCDIC::convertToEBCDIC(CompilationTime, CompilationTimeStr);
+  ConverterEBCDIC::convertToEBCDIC(Version, VersionStr);
+
+  enum class PPA2MemberId : uint8_t {
+    // See z/OS Language Environment Vendor Interfaces v2r5, p.23, for
+    // complete list. Only the C runtime is supported by this backend.
+    LE_C_Runtime = 3,
+  };
+  enum class PPA2MemberSubId : uint8_t {
+    // List of languages using the LE C runtime implementation.
+    C = 0x00,
+    CXX = 0x01,
+    Swift = 0x03,
+    Go = 0x60,
+    LLVMBasedLang = 0xe7,
+  };
+  // PPA2 Flags
+  enum class PPA2Flags : uint8_t {
+    CompileForBinaryFloatingPoint = 0x80,
+    CompiledWithXPLink = 0x01,
+    CompiledUnitASCII = 0x04,
+    HasServiceInfo = 0x20,
+  };
+
+  PPA2MemberSubId MemberSubId = PPA2MemberSubId::LLVMBasedLang;
+  if (auto *MD = M.getModuleFlag("zos_cu_language")) {
+    StringRef Language = cast<MDString>(MD)->getString();
+    MemberSubId = StringSwitch<PPA2MemberSubId>(Language)
+                      .Case("C", PPA2MemberSubId::C)
+                      .Case("CXX", PPA2MemberSubId::CXX)
+                      .Case("Swift", PPA2MemberSubId::Swift)
+                      .Case("Go", PPA2MemberSubId::Go)
+                      .Default(PPA2MemberSubId::LLVMBasedLang);
+  }
+
+  // Emit PPA2 section.
+  OutStreamer->emitLabel(PPA2Sym);
+  OutStreamer->emitInt8(static_cast<uint8_t>(PPA2MemberId::LE_C_Runtime));
+  OutStreamer->emitInt8(static_cast<uint8_t>(MemberSubId));
+  OutStreamer->emitInt8(0x22); // Member defined, c370_plist+c370_env
+  OutStreamer->emitInt8(0x04); // Control level 4 (XPLink)
+  OutStreamer->emitAbsoluteSymbolDiff(CELQSTRT, PPA2Sym, 4);
+  OutStreamer->emitInt32(0x00000000);
+  OutStreamer->emitAbsoluteSymbolDiff(DateVersionSym, PPA2Sym, 4);
+  OutStreamer->emitInt32(
+      0x00000000); // Offset to main entry point, always 0 (so says TR).
+  uint8_t Flgs = static_cast<uint8_t>(PPA2Flags::CompileForBinaryFloatingPoint);
+  Flgs |= static_cast<uint8_t>(PPA2Flags::CompiledWithXPLink);
+
+  if (auto *MD = M.getModuleFlag("zos_le_char_mode")) {
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uweigand wrote:

This is also nowhere set in clang right now.  Should it be?   If it isn't set, is EBCDIC the right default?

https://github.com/llvm/llvm-project/pull/68926