MC: Teach the COFF object writer to write address-significance tables.

The format is the same as in ELF: a sequence of ULEB128-encoded
symbol indexes.

Differential Revision: https://reviews.llvm.org/D51047

llvm-svn: 340499

1 files changed, 35 insertions, 0 deletions

diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp
index 4f6103c6d68..82c9fe76758 100644
--- a/llvm/lib/MC/WinCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp
@@ -36,6 +36,7 @@
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/JamCRC.h"
+#include "llvm/Support/LEB128.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
@@ -145,6 +146,10 @@ public:
 
   bool UseBigObj;
 
+  bool EmitAddrsigSection = false;
+  MCSectionCOFF *AddrsigSection;
+  std::vector<const MCSymbol *> AddrsigSyms;
+
   WinCOFFObjectWriter(std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW,
                       raw_pwrite_stream &OS);
 
@@ -204,6 +209,11 @@ public:
   void assignSectionNumbers();
   void assignFileOffsets(MCAssembler &Asm, const MCAsmLayout &Layout);
 
+  void emitAddrsigSection() override { EmitAddrsigSection = true; }
+  void addAddrsigSymbol(const MCSymbol *Sym) override {
+    AddrsigSyms.push_back(Sym);
+  }
+
   uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
 };
 
@@ -657,6 +667,13 @@ void WinCOFFObjectWriter::writeSection(MCAssembler &Asm,
 
 void WinCOFFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
                                                    const MCAsmLayout &Layout) {
+  if (EmitAddrsigSection) {
+    AddrsigSection = Asm.getContext().getCOFFSection(
+        ".llvm_addrsig", COFF::IMAGE_SCN_LNK_REMOVE,
+        SectionKind::getMetadata());
+    Asm.registerSection(*AddrsigSection);
+  }
+
   // "Define" each section & symbol. This creates section & symbol
   // entries in the staging area.
   for (const auto &Section : Asm)
@@ -1024,6 +1041,24 @@ uint64_t WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
     Section->Symbol->Aux[0].Aux.SectionDefinition.Number = AssocSec->Number;
   }
 
+  // Create the contents of the .llvm_addrsig section.
+  if (EmitAddrsigSection) {
+    auto Frag = new MCDataFragment(AddrsigSection);
+    raw_svector_ostream OS(Frag->getContents());
+    for (const MCSymbol *S : AddrsigSyms) {
+      if (!S->isTemporary()) {
+        encodeULEB128(S->getIndex(), OS);
+        continue;
+      }
+
+      MCSection *TargetSection = &S->getSection();
+      assert(SectionMap.find(TargetSection) != SectionMap.end() &&
+             "Section must already have been defined in "
+             "executePostLayoutBinding!");
+      encodeULEB128(SectionMap[TargetSection]->Symbol->getIndex(), OS);
+    }
+  }
+
   assignFileOffsets(Asm, Layout);
 
   // MS LINK expects to be able to use this timestamp to implement their