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

7 files changed, 256 insertions, 0 deletions

diff --git a/src/passes/CMakeLists.txt b/src/passes/CMakeLists.txt
index 8eb3c7e88..456854644 100644
--- a/src/passes/CMakeLists.txt
+++ b/src/passes/CMakeLists.txt
@@ -18,6 +18,7 @@ set(passes_SOURCES
   Directize.cpp
   DuplicateImportElimination.cpp
   DuplicateFunctionElimination.cpp
+  DWARF.cpp
   ExtractFunction.cpp
   Flatten.cpp
   FuncCastEmulation.cpp
diff --git a/src/passes/DWARF.cpp b/src/passes/DWARF.cpp
new file mode 100644
index 000000000..fe595adae
--- /dev/null
+++ b/src/passes/DWARF.cpp
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2019 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+//
+// Dump DWARF sections. This results in something similar to llvm-dwarfdump,
+// as it uses the same code.
+//
+// Note that this dumps the DWARF data read from the binary when we loaded it.
+// It does not contain changes made since then, which will only be updated
+// when we write the binary. To see those changes, you must round-trip.
+//
+
+#include "pass.h"
+#include "wasm-debug.h"
+#include "wasm.h"
+
+namespace wasm {
+
+struct DWARFDump : public Pass {
+  void run(PassRunner* runner, Module* module) override {
+    Debug::dumpDWARF(*module);
+  }
+};
+
+struct DWARFUpdate : public Pass {
+  void run(PassRunner* runner, Module* module) override {
+    Debug::writeDWARFSections(*module);
+  }
+};
+
+Pass* createDWARFDumpPass() { return new DWARFDump(); }
+
+Pass* createDWARFUpdatePass() { return new DWARFUpdate(); }
+
+} // namespace wasm
diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index 113017df5..cbc8e3be9 100644
--- a/src/passes/pass.cpp
+++ b/src/passes/pass.cpp
@@ -107,6 +107,11 @@ void PassRegistry::registerPasses() {
     "directize", "turns indirect calls into direct ones", createDirectizePass);
   registerPass(
     "dfo", "optimizes using the DataFlow SSA IR", createDataFlowOptsPass);
+  registerPass("dwarfdump",
+               "dump DWARF debug info sections from the read binary",
+               createDWARFDumpPass);
+  registerPass(
+    "dwarfupdate", "update DWARF debug info sections", createDWARFUpdatePass);
   registerPass("duplicate-import-elimination",
                "removes duplicate imports",
                createDuplicateImportEliminationPass);
diff --git a/src/passes/passes.h b/src/passes/passes.h
index 33a0b26da..2f30441db 100644
--- a/src/passes/passes.h
+++ b/src/passes/passes.h
@@ -35,6 +35,8 @@ Pass* createDAEOptimizingPass();
 Pass* createDataFlowOptsPass();
 Pass* createDeadCodeEliminationPass();
 Pass* createDirectizePass();
+Pass* createDWARFDumpPass();
+Pass* createDWARFUpdatePass();
 Pass* createDuplicateImportEliminationPass();
 Pass* createDuplicateFunctionEliminationPass();
 Pass* createEmitTargetFeaturesPass();
diff --git a/src/wasm-debug.h b/src/wasm-debug.h
new file mode 100644
index 000000000..d2e4840f1
--- /dev/null
+++ b/src/wasm-debug.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2019 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+//
+// Comprehensive debug info support (beyond source maps).
+//
+
+#ifndef wasm_wasm_debug_h
+#define wasm_wasm_debug_h
+
+#include <string>
+
+#include "wasm.h"
+
+namespace wasm {
+
+namespace Debug {
+
+bool isDWARFSection(Name name);
+
+bool hasDWARFSections(const Module& wasm);
+
+// Dump the DWARF sections to stdout.
+void dumpDWARF(const Module& wasm);
+
+// Update the DWARF sections.
+void writeDWARFSections(Module& wasm);
+
+} // namespace Debug
+
+} // namespace wasm
+
+#undef DEBUG_TYPE
+
+#endif // wasm_wasm_debug_h
diff --git a/src/wasm/CMakeLists.txt b/src/wasm/CMakeLists.txt
index dab974ea4..38bbc97fb 100644
--- a/src/wasm/CMakeLists.txt
+++ b/src/wasm/CMakeLists.txt
@@ -3,6 +3,7 @@ set(wasm_SOURCES
   wasm.cpp
   wasm-binary.cpp
   wasm-emscripten.cpp
+  wasm-debug.cpp
   wasm-interpreter.cpp
   wasm-io.cpp
   wasm-s-parser.cpp
diff --git a/src/wasm/wasm-debug.cpp b/src/wasm/wasm-debug.cpp
new file mode 100644
index 000000000..595c7f50b
--- /dev/null
+++ b/src/wasm/wasm-debug.cpp
@@ -0,0 +1,151 @@
+/*
+ * Copyright 2019 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "wasm-debug.h"
+#include "wasm.h"
+
+#ifdef BUILD_LLVM_DWARF
+#include "llvm/ObjectYAML/DWARFEmitter.h"
+#include "llvm/ObjectYAML/DWARFYAML.h"
+#include "llvm/include/llvm/DebugInfo/DWARFContext.h"
+
+std::error_code dwarf2yaml(llvm::DWARFContext& DCtx, llvm::DWARFYAML::Data& Y);
+#endif
+
+namespace wasm {
+
+namespace Debug {
+
+bool isDWARFSection(Name name) { return name.startsWith(".debug_"); }
+
+bool hasDWARFSections(const Module& wasm) {
+  for (auto& section : wasm.userSections) {
+    if (isDWARFSection(section.name)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+#ifdef BUILD_LLVM_DWARF
+
+struct BinaryenDWARFInfo {
+  llvm::StringMap<std::unique_ptr<llvm::MemoryBuffer>> sections;
+  std::unique_ptr<llvm::DWARFContext> context;
+
+  BinaryenDWARFInfo(const Module& wasm) {
+    // Get debug sections from the wasm.
+    for (auto& section : wasm.userSections) {
+      if (Name(section.name).startsWith(".debug_")) {
+        // TODO: efficiency
+        sections[section.name.substr(1)] = llvm::MemoryBuffer::getMemBufferCopy(
+          llvm::StringRef(section.data.data(), section.data.size()));
+      }
+    }
+    // Parse debug sections.
+    uint8_t addrSize = 4;
+    context = llvm::DWARFContext::create(sections, addrSize);
+  }
+};
+
+void dumpDWARF(const Module& wasm) {
+  BinaryenDWARFInfo info(wasm);
+  std::cout << "DWARF debug info\n";
+  std::cout << "================\n\n";
+  for (auto& section : wasm.userSections) {
+    if (Name(section.name).startsWith(".debug_")) {
+      std::cout << "Contains section " << section.name << " ("
+                << section.data.size() << " bytes)\n";
+    }
+  }
+  llvm::DIDumpOptions options;
+  options.Verbose = true;
+  info.context->dump(llvm::outs(), options);
+}
+
+//
+// Big picture: We use a DWARFContext to read data, then DWARFYAML support
+// code to write it. That is not the main LLVM Dwarf code used for writing
+// object files, but it avoids us create a "fake" MC layer, and provides a
+// simple way to write out the debug info. Likely the level of info represented
+// in the DWARFYAML::Data object is sufficient for Binaryen's needs, but if not,
+// we may need a different approach.
+//
+// In more detail:
+//
+// 1. Binary sections => DWARFContext:
+//
+//     llvm::DWARFContext::create(sections..)
+//
+// 2. DWARFContext => DWARFYAML::Data
+//
+//     std::error_code dwarf2yaml(DWARFContext &DCtx, DWARFYAML::Data &Y) {
+//
+// 3. DWARFYAML::Data => binary sections
+//
+//     StringMap<std::unique_ptr<MemoryBuffer>>
+//     EmitDebugSections(llvm::DWARFYAML::Data &DI, bool ApplyFixups);
+//
+// For modifying data, like line numberes, we can in theory do that either on
+// the DWARFContext or DWARFYAML::Data; unclear which is best, but modifying
+// the DWARFContext may save us doing fixups in EmitDebugSections.
+//
+
+void writeDWARFSections(Module& wasm) {
+  BinaryenDWARFInfo info(wasm);
+
+  // Convert to Data representation, which YAML can use to write.
+  llvm::DWARFYAML::Data Data;
+  if (dwarf2yaml(*info.context, Data)) {
+    Fatal() << "Failed to parse DWARF to YAML";
+  }
+
+  // TODO: Actually update, and remove sections we don't know how to update yet?
+
+  // Convert to binary sections.
+  auto newSections = EmitDebugSections(
+    Data,
+    false /* ApplyFixups, should be true if we modify Data, presumably? */);
+
+  // Update the custom sections in the wasm.
+  // TODO: efficiency
+  for (auto& section : wasm.userSections) {
+    if (Name(section.name).startsWith(".debug_")) {
+      auto llvmName = section.name.substr(1);
+      if (newSections.count(llvmName)) {
+        auto llvmData = newSections[llvmName]->getBuffer();
+        section.data.resize(llvmData.size());
+        std::copy(llvmData.begin(), llvmData.end(), section.data.data());
+      }
+    }
+  }
+}
+
+#else // BUILD_LLVM_DWARF
+
+void dumpDWARF(const Module& wasm) {
+  std::cerr << "warning: no DWARF dumping support present\n";
+}
+
+void writeDWARFSections(Module& wasm) {
+  std::cerr << "warning: no DWARF updating support present\n";
+}
+
+#endif // BUILD_LLVM_DWARF
+
+} // namespace Debug
+
+} // namespace wasm