[Dwarf/AArch64] Return address signing B key dwarf support

- When signing return addresses with -msign-return-address=<scope>{+<key>},
  either the A key instructions or the B key instructions can be used. To
  correctly authenticate the return address, the unwinder/debugger must know
  which key was used to sign the return address.
- When and exception is thrown or a break point reached, it may be necessary to
  unwind the stack. To accomplish this, the unwinder/debugger must be able to
  first authenticate an the return address if it has been signed.
- To enable this, the augmentation string of CIEs has been extended to allow
  inclusion of a 'B' character. Functions that are signed using the B key
  variant of the instructions should have and FDE whose associated CIE has a 'B'
  in the augmentation string.
- One must also be able to preserve these semantics when first stepping from a
  high level language into assembly and then, as a second step, into an object
  file. To achieve this, I have introduced a new assembly directive
  '.cfi_b_key_frame ', that tells the assembler the current frame uses return
  address signing with the B key.
- This ensures that the FDE is associated with a CIE that has 'B' in the
  augmentation string.

Differential Revision: https://reviews.llvm.org/D51798

llvm-svn: 349895

4 files changed, 33 insertions, 12 deletions

diff --git a/llvm/lib/MC/MCAsmStreamer.cpp b/llvm/lib/MC/MCAsmStreamer.cpp
index 4f0efab73e8..e017103070b 100644
--- a/llvm/lib/MC/MCAsmStreamer.cpp
+++ b/llvm/lib/MC/MCAsmStreamer.cpp
@@ -266,6 +266,7 @@ public:
   void EmitCVFPOData(const MCSymbol *ProcSym, SMLoc L) override;
 
   void EmitIdent(StringRef IdentString) override;
+  void EmitCFIBKeyFrame() override;
   void EmitCFISections(bool EH, bool Debug) override;
   void EmitCFIDefCfa(int64_t Register, int64_t Offset) override;
   void EmitCFIDefCfaOffset(int64_t Offset) override;
@@ -1602,6 +1603,12 @@ void MCAsmStreamer::EmitCFIReturnColumn(int64_t Register) {
   EmitEOL();
 }
 
+void MCAsmStreamer::EmitCFIBKeyFrame() {
+  MCStreamer::EmitCFIBKeyFrame();
+  OS << "\t.cfi_b_key_frame";
+  EmitEOL();
+}
+
 void MCAsmStreamer::EmitWinCFIStartProc(const MCSymbol *Symbol, SMLoc Loc) {
   MCStreamer::EmitWinCFIStartProc(Symbol, Loc);
 
diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index 9791fb5724b..38b02694d81 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -1565,9 +1565,8 @@ const MCSymbol &FrameEmitterImpl::EmitCIE(const MCDwarfFrameInfo &Frame) {
   uint8_t CIEVersion = getCIEVersion(IsEH, context.getDwarfVersion());
   Streamer.EmitIntValue(CIEVersion, 1);
 
-  // Augmentation String
-  SmallString<8> Augmentation;
   if (IsEH) {
+    SmallString<8> Augmentation;
     Augmentation += "z";
     if (Frame.Personality)
       Augmentation += "P";
@@ -1576,6 +1575,8 @@ const MCSymbol &FrameEmitterImpl::EmitCIE(const MCDwarfFrameInfo &Frame) {
     Augmentation += "R";
     if (Frame.IsSignalFrame)
       Augmentation += "S";
+    if (Frame.IsBKeyFrame)
+      Augmentation += "B";
     Streamer.EmitBytes(Augmentation);
   }
   Streamer.EmitIntValue(0, 1);
@@ -1730,25 +1731,28 @@ namespace {
 
 struct CIEKey {
   static const CIEKey getEmptyKey() {
-    return CIEKey(nullptr, 0, -1, false, false, static_cast<unsigned>(INT_MAX));
+    return CIEKey(nullptr, 0, -1, false, false, static_cast<unsigned>(INT_MAX),
+                  false);
   }
 
   static const CIEKey getTombstoneKey() {
-    return CIEKey(nullptr, -1, 0, false, false, static_cast<unsigned>(INT_MAX));
+    return CIEKey(nullptr, -1, 0, false, false, static_cast<unsigned>(INT_MAX),
+                  false);
   }
 
   CIEKey(const MCSymbol *Personality, unsigned PersonalityEncoding,
          unsigned LSDAEncoding, bool IsSignalFrame, bool IsSimple,
-         unsigned RAReg)
+         unsigned RAReg, bool IsBKeyFrame)
       : Personality(Personality), PersonalityEncoding(PersonalityEncoding),
         LsdaEncoding(LSDAEncoding), IsSignalFrame(IsSignalFrame),
-        IsSimple(IsSimple), RAReg(RAReg) {}
+        IsSimple(IsSimple), RAReg(RAReg), IsBKeyFrame(IsBKeyFrame) {}
 
   explicit CIEKey(const MCDwarfFrameInfo &Frame)
       : Personality(Frame.Personality),
         PersonalityEncoding(Frame.PersonalityEncoding),
         LsdaEncoding(Frame.LsdaEncoding), IsSignalFrame(Frame.IsSignalFrame),
-        IsSimple(Frame.IsSimple), RAReg(Frame.RAReg) {}
+        IsSimple(Frame.IsSimple), RAReg(Frame.RAReg),
+        IsBKeyFrame(Frame.IsBKeyFrame) {}
 
   const MCSymbol *Personality;
   unsigned PersonalityEncoding;
@@ -1756,6 +1760,7 @@ struct CIEKey {
   bool IsSignalFrame;
   bool IsSimple;
   unsigned RAReg;
+  bool IsBKeyFrame;
 };
 
 } // end anonymous namespace
@@ -1767,9 +1772,9 @@ template <> struct DenseMapInfo<CIEKey> {
   static CIEKey getTombstoneKey() { return CIEKey::getTombstoneKey(); }
 
   static unsigned getHashValue(const CIEKey &Key) {
-    return static_cast<unsigned>(
-        hash_combine(Key.Personality, Key.PersonalityEncoding, Key.LsdaEncoding,
-                     Key.IsSignalFrame, Key.IsSimple, Key.RAReg));
+    return static_cast<unsigned>(hash_combine(
+        Key.Personality, Key.PersonalityEncoding, Key.LsdaEncoding,
+        Key.IsSignalFrame, Key.IsSimple, Key.RAReg, Key.IsBKeyFrame));
   }
 
   static bool isEqual(const CIEKey &LHS, const CIEKey &RHS) {
@@ -1777,8 +1782,8 @@ template <> struct DenseMapInfo<CIEKey> {
            LHS.PersonalityEncoding == RHS.PersonalityEncoding &&
            LHS.LsdaEncoding == RHS.LsdaEncoding &&
            LHS.IsSignalFrame == RHS.IsSignalFrame &&
-           LHS.IsSimple == RHS.IsSimple &&
-           LHS.RAReg == RHS.RAReg;
+           LHS.IsSimple == RHS.IsSimple && LHS.RAReg == RHS.RAReg &&
+           LHS.IsBKeyFrame == RHS.IsBKeyFrame;
   }
 };
 
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index aa07eee4491..5c76c900c74 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -495,6 +495,7 @@ private:
     DK_CFI_UNDEFINED,
     DK_CFI_REGISTER,
     DK_CFI_WINDOW_SAVE,
+    DK_CFI_B_KEY_FRAME,
     DK_MACROS_ON,
     DK_MACROS_OFF,
     DK_ALTMACRO,
@@ -5293,6 +5294,7 @@ void AsmParser::initializeDirectiveKindMap() {
   DirectiveKindMap[".cfi_undefined"] = DK_CFI_UNDEFINED;
   DirectiveKindMap[".cfi_register"] = DK_CFI_REGISTER;
   DirectiveKindMap[".cfi_window_save"] = DK_CFI_WINDOW_SAVE;
+  DirectiveKindMap[".cfi_b_key_frame"] = DK_CFI_B_KEY_FRAME;
   DirectiveKindMap[".macros_on"] = DK_MACROS_ON;
   DirectiveKindMap[".macros_off"] = DK_MACROS_OFF;
   DirectiveKindMap[".macro"] = DK_MACRO;
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index 85e69f6f663..18fbea4afa0 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -221,6 +221,13 @@ void MCStreamer::emitDwarfFile0Directive(StringRef Directory,
                                       Source);
 }
 
+void MCStreamer::EmitCFIBKeyFrame() {
+  MCDwarfFrameInfo *CurFrame = getCurrentDwarfFrameInfo();
+  if (!CurFrame)
+    return;
+  CurFrame->IsBKeyFrame = true;
+}
+
 void MCStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                                        unsigned Column, unsigned Flags,
                                        unsigned Isa,