[WebAssembly] Add support for printing relocations with llvm-objdump

[sbc100]

Summary

This change also defines a relocatable wasm file as one that contains a
linking metadata section. This will allow tools such as lld to recognize
suitable input files.

[dschuff]

otherwise LGTM

tools/llvm-objdump/llvm-objdump.cpp

1085

LLVM style is "don't use else after return" (http://llvm.org/docs/CodingStandards.html#don-t-use-else-after-a-return)

[dschuff]

tools/llvm-objdump/llvm-objdump.cpp

1085

BTW I do like that you're adding the error case on fall though; I guess you could pretty much just remove all the elses and leave the ifs, and get the same thing.

[sbc100]

• No return after else

include/llvm/Object/Wasm.h

private:
   std::vector<wasm::WasmImport> Imports;
   std::vector<wasm::WasmExport> Exports;
   std::vector<wasm::WasmElemSegment> ElemSegments;
   std::vector<wasm::WasmDataSegment> DataSegments;
   std::vector<wasm::WasmFunction> Functions;
   std::vector<WasmSymbol> Symbols;
   ArrayRef<uint8_t> CodeSection;
   uint32_t StartFunction = -1;
+  bool HasLinkingSection = false;
   wasm::WasmLinkingData LinkingData;
 
   StringMap<uint32_t> SymbolMap;
 };
 
 } // end namespace object
 
 inline raw_ostream &operator<<(raw_ostream &OS,
                                const object::WasmSymbol &Sym) {
   Sym.print(OS);
   return OS;
 }
 
 } // end namespace llvm
 
 #endif // LLVM_OBJECT_WASM_H

lib/Object/WasmObjectFile.cpp

Error WasmObjectFile::parseNameSection(const uint8_t *Ptr, const uint8_t *End) {
   if (Ptr != End)
     return make_error<GenericBinaryError>("Name section ended prematurely",
                                           object_error::parse_failed);
   return Error::success();
 }
 
 Error WasmObjectFile::parseLinkingSection(const uint8_t *Ptr,
                                           const uint8_t *End) {
+  HasLinkingSection = true;
   while (Ptr < End) {
     uint8_t Type = readVarint7(Ptr);
     uint32_t Size = readVaruint32(Ptr);
     const uint8_t *SubSectionEnd = Ptr + Size;
     switch (Type) {
     case wasm::WASM_SYMBOL_INFO: {
       uint32_t Count = readVaruint32(Ptr);
       while (Count--) {

 StringRef WasmObjectFile::getFileFormatName() const { return "WASM"; }
 
 unsigned WasmObjectFile::getArch() const { return Triple::wasm32; }
 
 SubtargetFeatures WasmObjectFile::getFeatures() const {
   return SubtargetFeatures();
 }
 
-bool WasmObjectFile::isRelocatableObject() const { return false; }
+bool WasmObjectFile::isRelocatableObject() const {
+  return HasLinkingSection;
+}
 
 const WasmSection &WasmObjectFile::getWasmSection(DataRefImpl Ref) const {
   assert(Ref.d.a < Sections.size());
   return Sections[Ref.d.a];
 }
 
 const WasmSection &
 WasmObjectFile::getWasmSection(const SectionRef &Section) const {

test/tools/llvm-objdump/WebAssembly/relocations.test

+; RUN: llc -mtriple=wasm32-unknown-unknown-wasm -filetype=obj %s -o - | llvm-objdump -r - | FileCheck %s
+
+@foo = hidden global i32 1, align 4
+@bar = hidden global i32* @foo, align 4
+
+; CHECK:      RELOCATION RECORDS FOR [DATA]:
+; CHECK-NEXT: 0000000a R_WEBASSEMBLY_GLOBAL_ADDR_I32 0+0

tools/llvm-objdump/llvm-objdump.cpp

 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/COFF.h"
 #include "llvm/Object/COFFImportFile.h"
 #include "llvm/Object/ELFObjectFile.h"
 #include "llvm/Object/MachO.h"
 #include "llvm/Object/ObjectFile.h"
+#include "llvm/Object/Wasm.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/GraphWriter.h"
 #include "llvm/Support/Host.h"
if (isExtern) {
     // Adjust for the fact that sections are 1-indexed.
     advance(SI, Val - 1);
     SI->getName(S);
   }
 
   fmt << S;
 }
 
+static std::error_code getRelocationValueString(const WasmObjectFile *Obj,
+                                                const RelocationRef &RelRef,
+                                                SmallVectorImpl<char> &Result) {
+  const wasm::WasmRelocation& Rel = Obj->getWasmRelocation(RelRef);
+  std::string fmtbuf;
+  raw_string_ostream fmt(fmtbuf);
+  fmt << Rel.Index << (Rel.Addend < 0 ? "" : "+") << Rel.Addend;
+  fmt.flush();
+  Result.append(fmtbuf.begin(), fmtbuf.end());
+  return std::error_code();
+}
+
 static std::error_code getRelocationValueString(const MachOObjectFile *Obj,
                                                 const RelocationRef &RelRef,
                                                 SmallVectorImpl<char> &Result) {
   DataRefImpl Rel = RelRef.getRawDataRefImpl();
   MachO::any_relocation_info RE = Obj->getRelocation(Rel);
 
   unsigned Arch = Obj->getArch();
 
static std::error_code getRelocationValueString(const MachOObjectFile *Obj,
   return std::error_code();
 }
 
 static std::error_code getRelocationValueString(const RelocationRef &Rel,
                                                 SmallVectorImpl<char> &Result) {
   const ObjectFile *Obj = Rel.getObject();
   if (auto *ELF = dyn_cast<ELFObjectFileBase>(Obj))
     return getRelocationValueString(ELF, Rel, Result);
   if (auto *COFF = dyn_cast<COFFObjectFile>(Obj))
     return getRelocationValueString(COFF, Rel, Result);
-  auto *MachO = cast<MachOObjectFile>(Obj);
+  if (auto *Wasm = dyn_cast<WasmObjectFile>(Obj))
+    return getRelocationValueString(Wasm, Rel, Result);
+  if (auto *MachO = dyn_cast<MachOObjectFile>(Obj))
     return getRelocationValueString(MachO, Rel, Result);
+  llvm_unreachable("unknown object file format");
 }
 
 /// @brief Indicates whether this relocation should hidden when listing
 /// relocations, usually because it is the trailing part of a multipart
 /// relocation that will be printed as part of the leading relocation.
 static bool getHidden(RelocationRef RelRef) {
   const ObjectFile *Obj = RelRef.getObject();
   auto *MachO = dyn_cast<MachOObjectFile>(Obj);