[SystemZ][z/OS] Add exception handling for XPLINK (#74638)

Adds emitting the exception table and the EH registers for XPLINK.

---------

Co-authored-by: Yusra Syeda <[email protected]>

Author: ysyeda

llvm/include/llvm/CodeGen/CodeGenPassBuilder.h

@@ -695,6 +695,7 @@ void CodeGenPassBuilder<Derived>::addPassesToHandleExceptions(
   case ExceptionHandling::DwarfCFI:
   case ExceptionHandling::ARM:
   case ExceptionHandling::AIX:
+  case ExceptionHandling::ZOS:
     addPass(DwarfEHPreparePass(&TM));
     break;
   case ExceptionHandling::WinEH:

llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h

@@ -309,6 +309,8 @@ class TargetLoweringObjectFileGOFF : public TargetLoweringObjectFile {
                                     const TargetMachine &TM) const override;
   MCSection *getExplicitSectionGlobal(const GlobalObject *GO, SectionKind Kind,
                                       const TargetMachine &TM) const override;
+  MCSection *getSectionForLSDA(const Function &F, const MCSymbol &FnSym,
+                               const TargetMachine &TM) const override;
 };
 
 } // end namespace llvm

llvm/include/llvm/MC/MCAsmInfo.h

@@ -799,7 +799,8 @@ class MCAsmInfo {
   /// frame information to unwind.
   bool usesCFIForEH() const {
     return (ExceptionsType == ExceptionHandling::DwarfCFI ||
-            ExceptionsType == ExceptionHandling::ARM || usesWindowsCFI());
+            ExceptionsType == ExceptionHandling::ARM ||
+            ExceptionsType == ExceptionHandling::ZOS || usesWindowsCFI());
   }
 
   bool usesWindowsCFI() const {

llvm/include/llvm/MC/MCTargetOptions.h

@@ -24,6 +24,8 @@ enum class ExceptionHandling {
   WinEH,    ///< Windows Exception Handling
   Wasm,     ///< WebAssembly Exception Handling
   AIX,      ///< AIX Exception Handling
+  ZOS,      ///< z/OS MVS Exception Handling. Very similar to DwarfCFI, but the PPA1
+            ///< is used instead of an .eh_frame section.
 };
 
 enum class EmitDwarfUnwindType {

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -583,6 +583,7 @@ bool AsmPrinter::doInitialization(Module &M) {
     [[fallthrough]];
   case ExceptionHandling::SjLj:
   case ExceptionHandling::DwarfCFI:
+  case ExceptionHandling::ZOS:
     ES = new DwarfCFIException(this);
     break;
   case ExceptionHandling::ARM:

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -2681,6 +2681,13 @@ MCSection *TargetLoweringObjectFileGOFF::getExplicitSectionGlobal(
   return SelectSectionForGlobal(GO, Kind, TM);
 }
 
+MCSection *TargetLoweringObjectFileGOFF::getSectionForLSDA(
+    const Function &F, const MCSymbol &FnSym, const TargetMachine &TM) const {
+  std::string Name = ".gcc_exception_table." + F.getName().str();
+  return getContext().getGOFFSection(Name, SectionKind::getData(), nullptr,
+                                     nullptr);
+}
+
 MCSection *TargetLoweringObjectFileGOFF::SelectSectionForGlobal(
     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
   auto *Symbol = TM.getSymbol(GO);

llvm/lib/CodeGen/TargetPassConfig.cpp

@@ -947,6 +947,7 @@ void TargetPassConfig::addPassesToHandleExceptions() {
   case ExceptionHandling::DwarfCFI:
   case ExceptionHandling::ARM:
   case ExceptionHandling::AIX:
+  case ExceptionHandling::ZOS:
     addPass(createDwarfEHPass(getOptLevel()));
     break;
   case ExceptionHandling::WinEH:

llvm/lib/MC/MCContext.cpp

@@ -650,10 +650,16 @@ MCSectionGOFF *MCContext::getGOFFSection(StringRef Section, SectionKind Kind,
                                          MCSection *Parent,
                                          const MCExpr *SubsectionId) {
   // Do the lookup. If we don't have a hit, return a new section.
-  auto &GOFFSection = GOFFUniquingMap[Section.str()];
-  if (!GOFFSection)
-    GOFFSection = new (GOFFAllocator.Allocate())
-        MCSectionGOFF(Section, Kind, Parent, SubsectionId);
+  auto IterBool =
+      GOFFUniquingMap.insert(std::make_pair(Section.str(), nullptr));
+  auto Iter = IterBool.first;
+  if (!IterBool.second)
+    return Iter->second;
+
+  StringRef CachedName = Iter->first;
+  MCSectionGOFF *GOFFSection = new (GOFFAllocator.Allocate())
+      MCSectionGOFF(CachedName, Kind, Parent, SubsectionId);
+  Iter->second = GOFFSection;
 
   return GOFFSection;
 }

llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCAsmInfo.cpp

@@ -38,6 +38,7 @@ SystemZMCAsmInfoGOFF::SystemZMCAsmInfoGOFF(const Triple &TT) {
   DotIsPC = false;
   EmitGNUAsmStartIndentationMarker = false;
   EmitLabelsInUpperCase = true;
+  ExceptionsType = ExceptionHandling::ZOS;
   IsLittleEndian = false;
   MaxInstLength = 6;
   RestrictCommentStringToStartOfStatement = true;

llvm/lib/Target/SystemZ/SystemZAsmPrinter.cpp

@@ -1115,7 +1115,7 @@ void SystemZAsmPrinter::emitFunctionBodyEnd() {
 
 static void emitPPA1Flags(std::unique_ptr<MCStreamer> &OutStreamer, bool VarArg,
                           bool StackProtector, bool FPRMask, bool VRMask,
-                          bool HasName) {
+                          bool EHBlock, bool HasName) {
   enum class PPA1Flag1 : uint8_t {
     DSA64Bit = (0x80 >> 0),
     VarArg = (0x80 >> 7),
@@ -1133,6 +1133,7 @@ static void emitPPA1Flags(std::unique_ptr<MCStreamer> &OutStreamer, bool VarArg,
   enum class PPA1Flag4 : uint8_t {
     EPMOffsetPresent = (0x80 >> 0),
     VRMask = (0x80 >> 2),
+    EHBlock = (0x80 >> 3),
     ProcedureNamePresent = (0x80 >> 7),
     LLVM_MARK_AS_BITMASK_ENUM(EPMOffsetPresent)
   };
@@ -1158,6 +1159,9 @@ static void emitPPA1Flags(std::unique_ptr<MCStreamer> &OutStreamer, bool VarArg,
   if (VRMask)
     Flags4 |= PPA1Flag4::VRMask; // Add emit VR mask flag.
 
+  if (EHBlock)
+    Flags4 |= PPA1Flag4::EHBlock; // Add optional EH block.
+
   if (HasName)
     Flags4 |= PPA1Flag4::ProcedureNamePresent; // Add optional name block.
 
@@ -1188,6 +1192,8 @@ static void emitPPA1Flags(std::unique_ptr<MCStreamer> &OutStreamer, bool VarArg,
   OutStreamer->AddComment("PPA1 Flags 4");
   if ((Flags4 & PPA1Flag4::VRMask) == PPA1Flag4::VRMask)
     OutStreamer->AddComment("  Bit 2: 1 = Vector Reg Mask is in optional area");
+  if ((Flags4 & PPA1Flag4::EHBlock) == PPA1Flag4::EHBlock)
+    OutStreamer->AddComment("  Bit 3: 1 = C++ EH block");
   if ((Flags4 & PPA1Flag4::ProcedureNamePresent) ==
       PPA1Flag4::ProcedureNamePresent)
     OutStreamer->AddComment("  Bit 7: 1 = Name Length and Name");
@@ -1314,12 +1320,14 @@ void SystemZAsmPrinter::emitPPA1(MCSymbol *FnEndSym) {
   OutStreamer->AddComment("Offset to PPA2");
   OutStreamer->emitAbsoluteSymbolDiff(PPA2Sym, CurrentFnPPA1Sym, 4);
 
+  bool NeedEmitEHBlock = !MF->getLandingPads().empty();
+
   bool HasName =
       MF->getFunction().hasName() && MF->getFunction().getName().size() > 0;
 
   emitPPA1Flags(OutStreamer, MF->getFunction().isVarArg(),
                 MFFrame.hasStackProtectorIndex(), SavedFPRMask != 0,
-                TargetHasVector && SavedVRMask != 0, HasName);
+                TargetHasVector && SavedVRMask != 0, NeedEmitEHBlock, HasName);
 
   OutStreamer->AddComment("Length/4 of Parms");
   OutStreamer->emitInt16(
@@ -1361,6 +1369,29 @@ void SystemZAsmPrinter::emitPPA1(MCSymbol *FnEndSym) {
     OutStreamer->emitInt32(FrameAndVROffset);
   }
 
+  // Emit C++ EH information block
+  const Function *Per = nullptr;
+  if (NeedEmitEHBlock) {
+    Per = dyn_cast<Function>(
+        MF->getFunction().getPersonalityFn()->stripPointerCasts());
+    MCSymbol *PersonalityRoutine =
+        Per ? MF->getTarget().getSymbol(Per) : nullptr;
+    assert(PersonalityRoutine && "Missing personality routine");
+
+    OutStreamer->AddComment("Version");
+    OutStreamer->emitInt32(1);
+    OutStreamer->AddComment("Flags");
+    OutStreamer->emitInt32(0); // LSDA field is a WAS offset
+    OutStreamer->AddComment("Personality routine");
+    OutStreamer->emitInt64(ADATable.insert(
+        PersonalityRoutine, SystemZII::MO_ADA_INDIRECT_FUNC_DESC));
+    OutStreamer->AddComment("LSDA location");
+    MCSymbol *GCCEH = MF->getContext().getOrCreateSymbol(
+        Twine("GCC_except_table") + Twine(MF->getFunctionNumber()));
+    OutStreamer->emitInt64(
+        ADATable.insert(GCCEH, SystemZII::MO_ADA_DATA_SYMBOL_ADDR));
+  }
+
   // Emit name length and name optional section (0x01 of flags 4)
   if (HasName)
     emitPPA1Name(OutStreamer, MF->getFunction().getName());

llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp

@@ -17,6 +17,7 @@
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/RegisterScavenging.h"
+#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
 #include "llvm/IR/Function.h"
 #include "llvm/Target/TargetMachine.h"
 
@@ -994,6 +995,11 @@ bool SystemZXPLINKFrameLowering::assignCalleeSavedSpillSlots(
   if (hasFP(MF) || Subtarget.hasBackChain())
     CSI.push_back(CalleeSavedInfo(Regs.getStackPointerRegister()));
 
+  // If this function has an associated personality function then the
+  // environment register R5 must be saved in the DSA.
+  if (!MF.getLandingPads().empty())
+    CSI.push_back(CalleeSavedInfo(Regs.getADARegister()));
+
   // Scan the call-saved GPRs and find the bounds of the register spill area.
   Register LowRestoreGPR = 0;
   int LowRestoreOffset = INT32_MAX;

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -1362,6 +1362,16 @@ SystemZTargetLowering::getRegisterByName(const char *RegName, LLT VT,
   report_fatal_error("Invalid register name global variable");
 }
 
+Register SystemZTargetLowering::getExceptionPointerRegister(
+    const Constant *PersonalityFn) const {
+  return Subtarget.isTargetXPLINK64() ? SystemZ::R1D : SystemZ::R6D;
+}
+
+Register SystemZTargetLowering::getExceptionSelectorRegister(
+    const Constant *PersonalityFn) const {
+  return Subtarget.isTargetXPLINK64() ? SystemZ::R2D : SystemZ::R7D;
+}
+
 void SystemZTargetLowering::LowerAsmOperandForConstraint(
     SDValue Op, StringRef Constraint, std::vector<SDValue> &Ops,
     SelectionDAG &DAG) const {

llvm/lib/Target/SystemZ/SystemZISelLowering.h

@@ -555,16 +555,12 @@ class SystemZTargetLowering : public TargetLowering {
   /// If a physical register, this returns the register that receives the
   /// exception address on entry to an EH pad.
   Register
-  getExceptionPointerRegister(const Constant *PersonalityFn) const override {
-    return SystemZ::R6D;
-  }
+  getExceptionPointerRegister(const Constant *PersonalityFn) const override;
 
   /// If a physical register, this returns the register that receives the
   /// exception typeid on entry to a landing pad.
   Register
-  getExceptionSelectorRegister(const Constant *PersonalityFn) const override {
-    return SystemZ::R7D;
-  }
+  getExceptionSelectorRegister(const Constant *PersonalityFn) const override;
 
   /// Override to support customized stack guard loading.
   bool useLoadStackGuardNode() const override {

llvm/test/CodeGen/SystemZ/zos-landingpad.ll

@@ -0,0 +1,41 @@
+; RUN: llc < %s -mtriple=s390x-none-zos -mcpu=z10 | FileCheck %s
+;
+; Ensures that landingpad instructions use the right Exception Pointer
+; and Exception Selector registers, and that the exception table is emitted.
+
+declare void @callee()
+declare void @passeh(i8*, i32) noreturn
+declare i32 @__zos_cxx_personality_v2(...)
+
+define void @test1() uwtable personality i32 (...)* @__zos_cxx_personality_v2 {
+entry:
+  %ehptr = alloca i8*, align 8
+  %ehsel = alloca i32, align 8
+  invoke void @callee() to label %done unwind label %lpad
+done:
+  ret void
+; Match the return instruction.
+; CHECK: b 2(7)
+lpad:
+  %0 = landingpad { i8*, i32 } cleanup
+; The Exception Pointer is %r1; the Exception Selector, %r2.
+; CHECK: @BB{{[^%]*}} %lpad
+; CHECK-DAG: stg 1, {{.*}}
+; CHECK-DAG: st 2, {{.*}}
+  %1 = extractvalue { i8*, i32 } %0, 0
+  %2 = extractvalue { i8*, i32 } %0, 1
+  store i8* %1, i8** %ehptr, align 8
+  store i32 %2, i32* %ehsel, align 8
+  call void @passeh(i8* %1, i32 %2)
+  unreachable
+}
+
+; Check that offsets to the FD of the personality routine and LSDA are emitted in PPA1
+; CHECK: .byte 145 {{.*PPA1 Flags}}
+; CHECK: Bit 3: 1 = C++ EH block
+; TODO: Emit the value instead of a dummy value.
+; CHECK: Personality routine
+; CHECK: LSDA location
+; Check that the exception table is emitted into .lsda section.
+; CHECK: .section ".gcc_exception_table.test1"
+; CHECK: GCC_except_table0: