DWARF parsing and writing support using LLVM (#2520)

This imports LLVM code for DWARF handling. That code has the
Apache 2 license like us. It's also the same code used to
emit DWARF in the common toolchain, so it seems like a safe choice.

This adds two passes: --dwarfdump which runs the same code LLVM
runs for llvm-dwarfdump. This shows we can parse it ok, and will
be useful for debugging. And --dwarfupdate writes out the DWARF
sections (unchanged from what we read, so it just roundtrips - for
updating we need #2515).

This puts LLVM in thirdparty which is added here.

All the LLVM code is behind USE_LLVM_DWARF, which is on
by default, but off in JS for now, as it increases code size by 20%.

This current approach imports the LLVM files directly. This is not
how they are intended to be used, so it required a bunch of
local changes - more than I expected actually, for the platform-specific
stuff. For now this seems to work, so it may be good enough, but
in the long term we may want to switch to linking against libllvm.
A downside to doing that is that binaryen users would need to
have an LLVM build, and even in the waterfall builds we'd have a
problem - while we ship LLVM there anyhow, we constantly update
it, which means that binaryen would need to be on latest llvm all
the time too (which otherwise, given DWARF is quite stable, we
might not need to constantly update).

An even larger issue is that as I did this work I learned about how
DWARF works in LLVM, and while the reading code is easy to
reuse, the writing code is trickier. The main code path is heavily
integrated with the MC layer, which we don't have - we might want
to create a "fake MC layer" for that, but it sounds hard. Instead,
there is the YAML path which is used mostly for testing, and which
can convert DWARF to and from YAML and from binary. Using
the non-YAML parts there, we can convert binary DWARF to
the YAML layer's nice Info data, then convert that to binary. This
works, however, this is not the path LLVM uses normally, and it
supports only some basic DWARF sections - I had to add ranges
support, in fact. So if we need more complex things, we may end
up needing to use the MC layer approach, or consider some other
DWARF library. However, hopefully that should not affect the core
binaryen code which just calls a library for DWARF stuff.

Helps #2400

1 files changed, 110 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/MC/MCSymbolWasm.h b/third_party/llvm-project/include/llvm/MC/MCSymbolWasm.h
new file mode 100644
index 000000000..95beebe3f
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/MC/MCSymbolWasm.h
@@ -0,0 +1,110 @@
+//===- MCSymbolWasm.h -  ----------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_MC_MCSYMBOLWASM_H
+#define LLVM_MC_MCSYMBOLWASM_H
+
+#include "llvm/BinaryFormat/Wasm.h"
+#include "llvm/MC/MCSymbol.h"
+
+namespace llvm {
+
+class MCSymbolWasm : public MCSymbol {
+  wasm::WasmSymbolType Type = wasm::WASM_SYMBOL_TYPE_DATA;
+  bool IsWeak = false;
+  bool IsHidden = false;
+  bool IsComdat = false;
+  mutable bool IsUsedInGOT = false;
+  Optional<std::string> ImportModule;
+  Optional<std::string> ImportName;
+  wasm::WasmSignature *Signature = nullptr;
+  Optional<wasm::WasmGlobalType> GlobalType;
+  Optional<wasm::WasmEventType> EventType;
+
+  /// An expression describing how to calculate the size of a symbol. If a
+  /// symbol has no size this field will be NULL.
+  const MCExpr *SymbolSize = nullptr;
+
+public:
+  // Use a module name of "env" for now, for compatibility with existing tools.
+  // This is temporary, and may change, as the ABI is not yet stable.
+  MCSymbolWasm(const StringMapEntry<bool> *Name, bool isTemporary)
+      : MCSymbol(SymbolKindWasm, Name, isTemporary) {}
+  static bool classof(const MCSymbol *S) { return S->isWasm(); }
+
+  const MCExpr *getSize() const { return SymbolSize; }
+  void setSize(const MCExpr *SS) { SymbolSize = SS; }
+
+  bool isFunction() const { return Type == wasm::WASM_SYMBOL_TYPE_FUNCTION; }
+  bool isData() const { return Type == wasm::WASM_SYMBOL_TYPE_DATA; }
+  bool isGlobal() const { return Type == wasm::WASM_SYMBOL_TYPE_GLOBAL; }
+  bool isSection() const { return Type == wasm::WASM_SYMBOL_TYPE_SECTION; }
+  bool isEvent() const { return Type == wasm::WASM_SYMBOL_TYPE_EVENT; }
+  wasm::WasmSymbolType getType() const { return Type; }
+  void setType(wasm::WasmSymbolType type) { Type = type; }
+
+  bool isExported() const {
+    return getFlags() & wasm::WASM_SYMBOL_EXPORTED;
+  }
+  void setExported() const {
+    modifyFlags(wasm::WASM_SYMBOL_EXPORTED, wasm::WASM_SYMBOL_EXPORTED);
+  }
+
+  bool isNoStrip() const {
+    return getFlags() & wasm::WASM_SYMBOL_NO_STRIP;
+  }
+  void setNoStrip() const {
+    modifyFlags(wasm::WASM_SYMBOL_NO_STRIP, wasm::WASM_SYMBOL_NO_STRIP);
+  }
+
+  bool isWeak() const { return IsWeak; }
+  void setWeak(bool isWeak) { IsWeak = isWeak; }
+
+  bool isHidden() const { return IsHidden; }
+  void setHidden(bool isHidden) { IsHidden = isHidden; }
+
+  bool isComdat() const { return IsComdat; }
+  void setComdat(bool isComdat) { IsComdat = isComdat; }
+
+  const StringRef getImportModule() const {
+      if (ImportModule.hasValue()) {
+          return ImportModule.getValue();
+      }
+      return "env";
+  }
+  void setImportModule(StringRef Name) { ImportModule = Name; }
+
+  const StringRef getImportName() const {
+      if (ImportName.hasValue()) {
+          return ImportName.getValue();
+      }
+      return getName();
+  }
+  void setImportName(StringRef Name) { ImportName = Name; }
+
+  void setUsedInGOT() const { IsUsedInGOT = true; }
+  bool isUsedInGOT() const { return IsUsedInGOT; }
+
+  const wasm::WasmSignature *getSignature() const { return Signature; }
+  void setSignature(wasm::WasmSignature *Sig) { Signature = Sig; }
+
+  const wasm::WasmGlobalType &getGlobalType() const {
+    assert(GlobalType.hasValue());
+    return GlobalType.getValue();
+  }
+  void setGlobalType(wasm::WasmGlobalType GT) { GlobalType = GT; }
+
+  const wasm::WasmEventType &getEventType() const {
+    assert(EventType.hasValue());
+    return EventType.getValue();
+  }
+  void setEventType(wasm::WasmEventType ET) { EventType = ET; }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_MC_MCSYMBOLWASM_H