[RISCV][ELF] Emit .gnu.note.property for Zicfiss/Zicfilip(CFI extension)

Author: SuHo-llrr

llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp

@@ -77,6 +77,33 @@ void RISCVTargetELFStreamer::finishAttributeSection() {
                           ELF::SHT_RISCV_ATTRIBUTES, AttributeSection);
 }
 
+void RISCVTargetELFStreamer::emitNoteSection(unsigned Flags) {
+  if (Flags == 0)
+    return;
+
+  MCStreamer &OutStreamer = getStreamer();
+  MCContext &Context = OutStreamer.getContext();
+  MCSectionELF *Nt = Context.getELFSection(".note.gnu.property", ELF::SHT_NOTE, ELF::SHF_ALLOC);
+  MCSection *Cur = OutStreamer.getCurrentSectionOnly();
+  OutStreamer.switchSection(Nt);
+
+  // Emit the note header.
+  OutStreamer.emitValueToAlignment(Align(8));
+  OutStreamer.emitIntValue(4, 4);     // data size for note name
+  OutStreamer.emitIntValue(4 * 4, 4); // data size
+  OutStreamer.emitIntValue(ELF::NT_GNU_PROPERTY_TYPE_0, 4); // note type
+  OutStreamer.emitBytes(StringRef("GNU", 4)); // note name
+
+  // Emit the CFI(ZICFILP/ZICFISS) properties.
+  OutStreamer.emitIntValue(ELF::GNU_PROPERTY_RISCV_FEATURE_1_AND, 4); // and property
+  OutStreamer.emitIntValue(4, 4);     // data size
+  OutStreamer.emitIntValue(Flags, 4); // data
+  OutStreamer.emitIntValue(0, 4);     // pad
+
+  OutStreamer.endSection(Nt);
+  OutStreamer.switchSection(Cur);
+}
+
 void RISCVTargetELFStreamer::finish() {
   RISCVTargetStreamer::finish();
   MCAssembler &MCA = getStreamer().getAssembler();
@@ -111,6 +138,19 @@ void RISCVTargetELFStreamer::finish() {
   }
 
   MCA.setELFHeaderEFlags(EFlags);
+
+  unsigned GNUNoteFlags = 0;
+
+  // TODO check ZICFILP or ZICFISS with march
+  // should we check with codegen enable ex. -mllvm
+  // -riscv-hardware-shadow-stack=true ?
+  if (Features[RISCV::FeatureStdExtZicfilp])
+    GNUNoteFlags |= ELF::GNU_PROPERTY_RISCV_FEATURE_1_ZICFILP;
+
+  if (Features[RISCV::FeatureStdExtZicfiss])
+    GNUNoteFlags |= ELF::GNU_PROPERTY_RISCV_FEATURE_1_ZICFISS;
+
+  emitNoteSection(GNUNoteFlags);
 }
 
 void RISCVTargetELFStreamer::reset() {

llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.h

@@ -71,6 +71,7 @@ class RISCVTargetELFStreamer : public RISCVTargetStreamer {
   void emitDirectiveVariantCC(MCSymbol &Symbol) override;
 
   void finish() override;
+  void emitNoteSection(unsigned Flags);
 };
 
 MCELFStreamer *createRISCVELFStreamer(MCContext &C,