From 0f8c06fb12ea8695463b64563ee245c83c3f39b2 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Mon, 30 Mar 2020 17:37:01 -0700
Subject: [PATCH] [WebAssembly] Emit .llvmcmd and .llvmbc as custom sections

Fixes: https://bugs.llvm.org/show_bug.cgi?id=45362

Differential Revision: https://reviews.llvm.org/D77115
---
 include/llvm/MC/MCSymbolWasm.h               |  4 ++++
 lib/CodeGen/TargetLoweringObjectFileImpl.cpp |  8 ++++++++
 lib/MC/WasmObjectWriter.cpp                  | 19 +++++++++----------
 3 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/include/llvm/MC/MCSymbolWasm.h b/include/llvm/MC/MCSymbolWasm.h
index da9525922fa..ffd8a7aad31 100644
--- a/include/llvm/MC/MCSymbolWasm.h
+++ b/include/llvm/MC/MCSymbolWasm.h
@@ -18,6 +18,7 @@ class MCSymbolWasm : public MCSymbol {
   bool IsWeak = false;
   bool IsHidden = false;
   bool IsComdat = false;
+  mutable bool IsUsedInInitArray = false;
   mutable bool IsUsedInGOT = false;
   Optional<StringRef> ImportModule;
   Optional<StringRef> ImportName;
@@ -96,6 +97,9 @@ public:
   void setUsedInGOT() const { IsUsedInGOT = true; }
   bool isUsedInGOT() const { return IsUsedInGOT; }
 
+  void setUsedInInitArray() const { IsUsedInInitArray = true; }
+  bool isUsedInInitArray() const { return IsUsedInInitArray; }
+
   const wasm::WasmSignature *getSignature() const { return Signature; }
   void setSignature(wasm::WasmSignature *Sig) { Signature = Sig; }
 
diff --git a/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 17946696a26..e7750ccf3ad 100644
--- a/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -1755,6 +1755,14 @@ MCSection *TargetLoweringObjectFileWasm::getExplicitSectionGlobal(
 
   StringRef Name = GO->getSection();
 
+  // Certain data sections we treat as named custom sections rather than
+  // segments within the data section.
+  // This could be avoided if all data segements (the wasm sense) were
+  // represented as thier own sections (in the llvm sense).
+  // TODO(sbc): https://github.com/WebAssembly/tool-conventions/issues/138
+  if (Name == ".llvmcmd" || Name == ".llvmbc")
+    Kind = SectionKind::getMetadata();
+
   StringRef Group = "";
   if (const Comdat *C = getWasmComdat(GO)) {
     Group = C->getName();
diff --git a/lib/MC/WasmObjectWriter.cpp b/lib/MC/WasmObjectWriter.cpp
index 321f93d7609..4df809224ed 100644
--- a/lib/MC/WasmObjectWriter.cpp
+++ b/lib/MC/WasmObjectWriter.cpp
@@ -436,10 +436,6 @@ void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
   uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
   MCContext &Ctx = Asm.getContext();
 
-  // The .init_array isn't translated as data, so don't do relocations in it.
-  if (FixupSection.getSectionName().startswith(".init_array"))
-    return;
-
   if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
     // To get here the A - B expression must have failed evaluateAsRelocatable.
     // This means either A or B must be undefined and in WebAssembly we can't
@@ -456,6 +452,12 @@ void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
   const MCSymbolRefExpr *RefA = Target.getSymA();
   const auto *SymA = cast<MCSymbolWasm>(&RefA->getSymbol());
 
+  // The .init_array isn't translated as data, so don't do relocations in it.
+  if (FixupSection.getSectionName().startswith(".init_array")) {
+    SymA->setUsedInInitArray();
+    return;
+  }
+
   if (SymA->isVariable()) {
     const MCExpr *Expr = SymA->getVariableValue();
     const auto *Inner = cast<MCSymbolRefExpr>(Expr);
@@ -1084,16 +1086,13 @@ void WasmObjectWriter::registerEventType(const MCSymbolWasm &Symbol) {
 }
 
 static bool isInSymtab(const MCSymbolWasm &Sym) {
-  if (Sym.isUsedInReloc())
+  if (Sym.isUsedInReloc() || Sym.isUsedInInitArray())
     return true;
 
   if (Sym.isComdat() && !Sym.isDefined())
     return false;
 
-  if (Sym.isTemporary() && Sym.getName().empty())
-    return false;
-
-  if (Sym.isTemporary() && Sym.isData() && !Sym.getSize())
+  if (Sym.isTemporary())
     return false;
 
   if (Sym.isSection())
@@ -1565,7 +1564,7 @@ uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
         report_fatal_error("fixups in .init_array should be symbol references");
       const auto &TargetSym = cast<const MCSymbolWasm>(SymRef->getSymbol());
       if (TargetSym.getIndex() == InvalidIndex)
-        report_fatal_error("symbols in .init_array should exist in symbtab");
+        report_fatal_error("symbols in .init_array should exist in symtab");
       if (!TargetSym.isFunction())
         report_fatal_error("symbols in .init_array should be for functions");
       InitFuncs.push_back(