[cfi] Add flag to always generate .debug_frame

This adds a flag to LLVM and clang to always generate a .debug_frame
section, even if other debug information is not being generated. In
situations where .eh_frame would normally be emitted, both .debug_frame
and .eh_frame will be used.

Differential Revision: https://reviews.llvm.org/D67216

clang/include/clang/Basic/CodeGenOptions.def

@@ -97,6 +97,8 @@ CODEGENOPT(CFProtectionBranch , 1, 0) ///< if -fcf-protection is
 CODEGENOPT(XRayInstrumentFunctions , 1, 0) ///< Set when -fxray-instrument is
                                            ///< enabled.
 CODEGENOPT(StackSizeSection  , 1, 0) ///< Set when -fstack-size-section is enabled.
+CODEGENOPT(ForceDwarfFrameSection , 1, 0) ///< Set when -fforce-dwarf-frame is
+                                          ///< enabled.
 
 ///< Set when -fxray-always-emit-customevents is enabled.
 CODEGENOPT(XRayAlwaysEmitCustomEvents , 1, 0)

clang/include/clang/Driver/Options.td

@@ -1950,6 +1950,10 @@ def fdebug_prefix_map_EQ
   : Joined<["-"], "fdebug-prefix-map=">, Group<f_Group>,
     Flags<[CC1Option,CC1AsOption]>,
     HelpText<"remap file source paths in debug info">;
+def fforce_dwarf_frame : Flag<["-"], "fforce-dwarf-frame">, Group<f_Group>, Flags<[CC1Option]>,
+    HelpText<"Always emit a debug frame section">;
+def fno_force_dwarf_frame : Flag<["-"], "fno-force-dwarf-frame">, Group<f_Group>, Flags<[CC1Option]>,
+    HelpText<"Don't always emit a debug frame section">;
 def g_Flag : Flag<["-"], "g">, Group<g_Group>,
   HelpText<"Generate source-level debug information">;
 def gline_tables_only : Flag<["-"], "gline-tables-only">, Group<gN_Group>,

clang/lib/CodeGen/BackendUtil.cpp

@@ -485,6 +485,7 @@ static void initTargetOptions(llvm::TargetOptions &Options,
   Options.EmitStackSizeSection = CodeGenOpts.StackSizeSection;
   Options.EmitAddrsig = CodeGenOpts.Addrsig;
   Options.EnableDebugEntryValues = CodeGenOpts.EnableDebugEntryValues;
+  Options.ForceDwarfFrameSection = CodeGenOpts.ForceDwarfFrameSection;
 
   Options.MCOptions.SplitDwarfFile = CodeGenOpts.SplitDwarfFile;
   Options.MCOptions.MCRelaxAll = CodeGenOpts.RelaxAll;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3339,6 +3339,10 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
     CmdArgs.push_back("-generate-arange-section");
   }
 
+  if (Args.hasFlag(options::OPT_fforce_dwarf_frame,
+                   options::OPT_fno_force_dwarf_frame, false))
+    CmdArgs.push_back("-fforce-dwarf-frame");
+
   if (Args.hasFlag(options::OPT_fdebug_types_section,
                    options::OPT_fno_debug_types_section, false)) {
     if (!T.isOSBinFormatELF()) {

clang/lib/Frontend/CompilerInvocation.cpp

@@ -769,6 +769,9 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.DebugFwdTemplateParams = Args.hasArg(OPT_debug_forward_template_params);
   Opts.EmbedSource = Args.hasArg(OPT_gembed_source);
 
+  Opts.ForceDwarfFrameSection =
+      Args.hasFlag(OPT_fforce_dwarf_frame, OPT_fno_force_dwarf_frame, false);
+
   for (const auto &Arg : Args.getAllArgValues(OPT_fdebug_prefix_map_EQ))
     Opts.DebugPrefixMap.insert(StringRef(Arg).split('='));
 

clang/test/Driver/fforce-dwarf-frame.c

@@ -0,0 +1,6 @@
+// RUN: %clang -target arm -c -### %s -fforce-dwarf-frame 2>&1 | FileCheck --check-prefix=CHECK-ALWAYS %s
+// RUN: %clang -target arm -c -### %s -fno-force-dwarf-frame 2>&1 | FileCheck --check-prefix=CHECK-NO-ALWAYS %s
+// RUN: %clang -target arm -c -### %s 2>&1 | FileCheck --check-prefix=CHECK-NO-ALWAYS %s
+
+// CHECK-ALWAYS: -fforce-dwarf-frame
+// CHECK-NO-ALWAYS-NOT: -fforce-dwarf-frame

llvm/include/llvm/CodeGen/CommandFlags.inc

@@ -276,6 +276,11 @@ static cl::opt<bool>
                            cl::desc("Emit debug info about parameter's entry values"),
                            cl::init(false));
 
+static cl::opt<bool>
+    ForceDwarfFrameSection("force-dwarf-frame-section",
+                           cl::desc("Always emit a debug frame section."),
+                           cl::init(false));
+
 // Common utility function tightly tied to the options listed here. Initializes
 // a TargetOptions object with CodeGen flags and returns it.
 static TargetOptions InitTargetOptionsFromCodeGenFlags() {
@@ -306,6 +311,7 @@ static TargetOptions InitTargetOptionsFromCodeGenFlags() {
   Options.EmitStackSizeSection = EnableStackSizeSection;
   Options.EmitAddrsig = EnableAddrsig;
   Options.EnableDebugEntryValues = EnableDebugEntryValues;
+  Options.ForceDwarfFrameSection = ForceDwarfFrameSection;
 
   Options.MCOptions = InitMCTargetOptionsFromFlags();
 

llvm/include/llvm/CodeGen/MachineFunction.h

@@ -560,6 +560,9 @@ public:
   }
   void setHasWinCFI(bool v) { HasWinCFI = v; }
 
+  /// True if this function needs frame moves for debug or exceptions.
+  bool needsFrameMoves() const;
+
   /// Get the function properties
   const MachineFunctionProperties &getProperties() const { return Properties; }
   MachineFunctionProperties &getProperties() { return Properties; }

llvm/include/llvm/Target/TargetOptions.h

@@ -119,7 +119,7 @@ namespace llvm {
           ExplicitEmulatedTLS(false), EnableIPRA(false),
           EmitStackSizeSection(false), EnableMachineOutliner(false),
           SupportsDefaultOutlining(false), EmitAddrsig(false),
-          EnableDebugEntryValues(false) {}
+          EnableDebugEntryValues(false), ForceDwarfFrameSection(false) {}
 
     /// PrintMachineCode - This flag is enabled when the -print-machineinstrs
     /// option is specified on the command line, and should enable debugging
@@ -256,6 +256,9 @@ namespace llvm {
     /// Emit debug info about parameter's entry values.
     unsigned EnableDebugEntryValues : 1;
 
+    /// Emit DWARF debug frame section.
+    unsigned ForceDwarfFrameSection : 1;
+
     /// FloatABIType - This setting is set by -float-abi=xxx option is specfied
     /// on the command line. This setting may either be Default, Soft, or Hard.
     /// Default selects the target's default behavior. Soft selects the ABI for

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -935,7 +935,7 @@ AsmPrinter::CFIMoveType AsmPrinter::needsCFIMoves() const {
       MF->getFunction().needsUnwindTableEntry())
     return CFI_M_EH;
 
-  if (MMI->hasDebugInfo())
+  if (MMI->hasDebugInfo() || MF->getTarget().Options.ForceDwarfFrameSection)
     return CFI_M_Debug;
 
   return CFI_M_None;

llvm/lib/CodeGen/AsmPrinter/DwarfCFIException.cpp

@@ -29,6 +29,7 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FormattedStream.h"
 #include "llvm/Target/TargetLoweringObjectFile.h"
+#include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetOptions.h"
 using namespace llvm;
 
@@ -133,6 +134,8 @@ void DwarfCFIException::beginFragment(const MachineBasicBlock *MBB,
   if (!hasEmittedCFISections) {
     if (Asm->needsOnlyDebugCFIMoves())
       Asm->OutStreamer->EmitCFISections(false, true);
+    else if (Asm->TM.Options.ForceDwarfFrameSection)
+      Asm->OutStreamer->EmitCFISections(true, true);
     hasEmittedCFISections = true;
   }
 

llvm/lib/CodeGen/CFIInstrInserter.cpp

@@ -48,8 +48,7 @@ class CFIInstrInserter : public MachineFunctionPass {
   }
 
   bool runOnMachineFunction(MachineFunction &MF) override {
-    if (!MF.getMMI().hasDebugInfo() &&
-        !MF.getFunction().needsUnwindTableEntry())
+    if (!MF.needsFrameMoves())
       return false;
 
     MBBVector.resize(MF.getNumBlockIDs());

llvm/lib/CodeGen/MachineFunction.cpp

@@ -520,6 +520,13 @@ void MachineFunction::print(raw_ostream &OS, const SlotIndexes *Indexes) const {
   OS << "\n# End machine code for function " << getName() << ".\n\n";
 }
 
+/// True if this function needs frame moves for debug or exceptions.
+bool MachineFunction::needsFrameMoves() const {
+  return getMMI().hasDebugInfo() ||
+         getTarget().Options.ForceDwarfFrameSection ||
+         F.needsUnwindTableEntry();
+}
+
 namespace llvm {
 
   template<>

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -844,8 +844,8 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
   const TargetInstrInfo *TII = Subtarget.getInstrInfo();
   MachineModuleInfo &MMI = MF.getMMI();
   AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
-  bool needsFrameMoves = (MMI.hasDebugInfo() || F.needsUnwindTableEntry()) &&
-                         !MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
+  bool needsFrameMoves =
+      MF.needsFrameMoves() && !MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
   bool HasFP = hasFP(MF);
   bool NeedsWinCFI = needsWinCFI(MF);
   bool HasWinCFI = false;

llvm/lib/Target/ARC/ARCRegisterInfo.cpp

@@ -128,7 +128,7 @@ static void ReplaceFrameIndex(MachineBasicBlock::iterator II,
 ARCRegisterInfo::ARCRegisterInfo() : ARCGenRegisterInfo(ARC::BLINK) {}
 
 bool ARCRegisterInfo::needsFrameMoves(const MachineFunction &MF) {
-  return MF.getMMI().hasDebugInfo() || MF.getFunction().needsUnwindTableEntry();
+  return MF.needsFrameMoves();
 }
 
 const MCPhysReg *

llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp

@@ -223,8 +223,7 @@ namespace {
 
 bool HexagonCallFrameInformation::runOnMachineFunction(MachineFunction &MF) {
   auto &HFI = *MF.getSubtarget<HexagonSubtarget>().getFrameLowering();
-  bool NeedCFI = MF.getMMI().hasDebugInfo() ||
-                 MF.getFunction().needsUnwindTableEntry();
+  bool NeedCFI = MF.needsFrameMoves();
 
   if (!NeedCFI)
     return false;

llvm/lib/Target/PowerPC/PPCFrameLowering.cpp

@@ -782,8 +782,7 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF,
   MachineModuleInfo &MMI = MF.getMMI();
   const MCRegisterInfo *MRI = MMI.getContext().getRegisterInfo();
   DebugLoc dl;
-  bool needsCFI = MMI.hasDebugInfo() ||
-    MF.getFunction().needsUnwindTableEntry();
+  bool needsCFI = MF.needsFrameMoves();
 
   // Get processor type.
   bool isPPC64 = Subtarget.isPPC64();

llvm/lib/Target/X86/X86FrameLowering.cpp

@@ -993,8 +993,7 @@ void X86FrameLowering::emitPrologue(MachineFunction &MF,
   bool NeedsWinFPO =
       !IsFunclet && STI.isTargetWin32() && MMI.getModule()->getCodeViewFlag();
   bool NeedsWinCFI = NeedsWin64CFI || NeedsWinFPO;
-  bool NeedsDwarfCFI =
-      !IsWin64Prologue && (MMI.hasDebugInfo() || Fn.needsUnwindTableEntry());
+  bool NeedsDwarfCFI = !IsWin64Prologue && MF.needsFrameMoves();
   Register FramePtr = TRI->getFrameRegister(MF);
   const Register MachineFramePtr =
       STI.isTarget64BitILP32()
@@ -1614,10 +1613,9 @@ void X86FrameLowering::emitEpilogue(MachineFunction &MF,
   bool HasFP = hasFP(MF);
   uint64_t NumBytes = 0;
 
-  bool NeedsDwarfCFI =
-      (!MF.getTarget().getTargetTriple().isOSDarwin() &&
-       !MF.getTarget().getTargetTriple().isOSWindows()) &&
-      (MF.getMMI().hasDebugInfo() || MF.getFunction().needsUnwindTableEntry());
+  bool NeedsDwarfCFI = (!MF.getTarget().getTargetTriple().isOSDarwin() &&
+                        !MF.getTarget().getTargetTriple().isOSWindows()) &&
+                       MF.needsFrameMoves();
 
   if (IsFunclet) {
     assert(HasFP && "EH funclets without FP not yet implemented");
@@ -2812,11 +2810,9 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
     unsigned StackAlign = getStackAlignment();
     Amount = alignTo(Amount, StackAlign);
 
-    MachineModuleInfo &MMI = MF.getMMI();
     const Function &F = MF.getFunction();
     bool WindowsCFI = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
-    bool DwarfCFI = !WindowsCFI &&
-                    (MMI.hasDebugInfo() || F.needsUnwindTableEntry());
+    bool DwarfCFI = !WindowsCFI && MF.needsFrameMoves();
 
     // If we have any exception handlers in this function, and we adjust
     // the SP before calls, we may need to indicate this to the unwinder

llvm/lib/Target/X86/X86InstrInfo.cpp

@@ -3963,9 +3963,7 @@ static bool ExpandMOVImmSExti8(MachineInstrBuilder &MIB,
   MachineFunction &MF = *MBB.getParent();
   const X86FrameLowering *TFL = Subtarget.getFrameLowering();
   bool IsWin64Prologue = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
-  bool NeedsDwarfCFI =
-      !IsWin64Prologue &&
-      (MF.getMMI().hasDebugInfo() || MF.getFunction().needsUnwindTableEntry());
+  bool NeedsDwarfCFI = !IsWin64Prologue && MF.needsFrameMoves();
   bool EmitCFI = !TFL->hasFP(MF) && NeedsDwarfCFI;
   if (EmitCFI) {
     TFL->BuildCFI(MBB, I, DL,

llvm/lib/Target/XCore/XCoreRegisterInfo.cpp

@@ -203,7 +203,7 @@ static void InsertSPConstInst(MachineBasicBlock::iterator II,
 }
 
 bool XCoreRegisterInfo::needsFrameMoves(const MachineFunction &MF) {
-  return MF.getMMI().hasDebugInfo() || MF.getFunction().needsUnwindTableEntry();
+  return MF.needsFrameMoves();
 }
 
 const MCPhysReg *

llvm/test/CodeGen/ARM/dwarf-frame.ll

@@ -0,0 +1,38 @@
+; RUN: llc -mtriple armv7-unknown -frame-pointer=all -filetype=asm -o - %s | FileCheck %s --check-prefix=CHECK-NO-CFI
+; RUN: llc -mtriple armv7-unknown -frame-pointer=all -filetype=asm -force-dwarf-frame-section -o - %s | FileCheck %s --check-prefix=CHECK-ALWAYS-CFI
+
+declare void @dummy_use(i32*, i32)
+
+define void @test_basic() #0 {
+        %mem = alloca i32, i32 10
+        call void @dummy_use (i32* %mem, i32 10)
+  ret void
+}
+
+; CHECK-NO-CFI-LABEL: test_basic:
+; CHECK-NO-CFI:   .fnstart
+; CHECK-NO-CFI-NOT:   .cfi_sections .debug_frame
+; CHECK-NO-CFI-NOT:   .cfi_startproc
+; CHECK-NO-CFI:       @ %bb.0:
+; CHECK-NO-CFI:       push {r11, lr}
+; CHECK-NO-CFI-NOT:   .cfi_def_cfa_offset 8
+; CHECK-NO-CFI-NOT:   .cfi_offset lr, -4
+; CHECK-NO-CFI-NOT:   .cfi_offset r11, -8
+; CHECK-NO-CFI:       mov r11, sp
+; CHECK-NO-CFI-NOT:   .cfi_def_cfa_register r11
+; CHECK-NO-CFI-NOT:   .cfi_endproc
+; CHECK-NO-CFI:       .fnend
+
+; CHECK-ALWAYS-CFI-LABEL: test_basic:
+; CHECK-ALWAYS-CFI:   .fnstart
+; CHECK-ALWAYS-CFI:   .cfi_sections .debug_frame
+; CHECK-ALWAYS-CFI:   .cfi_startproc
+; CHECK-ALWAYS-CFI:   @ %bb.0:
+; CHECK-ALWAYS-CFI:   push {r11, lr}
+; CHECK-ALWAYS-CFI:   .cfi_def_cfa_offset 8
+; CHECK-ALWAYS-CFI:   .cfi_offset lr, -4
+; CHECK-ALWAYS-CFI:   .cfi_offset r11, -8
+; CHECK-ALWAYS-CFI:   mov r11, sp
+; CHECK-ALWAYS-CFI:   .cfi_def_cfa_register r11
+; CHECK-ALWAYS-CFI:   .cfi_endproc
+; CHECK-ALWAYS-CFI:   .fnend