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, 273 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Support/BinaryByteStream.h b/third_party/llvm-project/include/llvm/Support/BinaryByteStream.h
new file mode 100644
index 000000000..7acce9a03
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Support/BinaryByteStream.h
@@ -0,0 +1,273 @@
+//===- BinaryByteStream.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
+//===----------------------------------------------------------------------===//
+// A BinaryStream which stores data in a single continguous memory buffer.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_BINARYBYTESTREAM_H
+#define LLVM_SUPPORT_BINARYBYTESTREAM_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/BinaryStream.h"
+#include "llvm/Support/BinaryStreamError.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/FileOutputBuffer.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include <algorithm>
+#include <cstdint>
+#include <cstring>
+#include <memory>
+
+namespace llvm {
+
+/// An implementation of BinaryStream which holds its entire data set
+/// in a single contiguous buffer.  BinaryByteStream guarantees that no read
+/// operation will ever incur a copy.  Note that BinaryByteStream does not
+/// own the underlying buffer.
+class BinaryByteStream : public BinaryStream {
+public:
+  BinaryByteStream() = default;
+  BinaryByteStream(ArrayRef<uint8_t> Data, llvm::support::endianness Endian)
+      : Endian(Endian), Data(Data) {}
+  BinaryByteStream(StringRef Data, llvm::support::endianness Endian)
+      : Endian(Endian), Data(Data.bytes_begin(), Data.bytes_end()) {}
+
+  llvm::support::endianness getEndian() const override { return Endian; }
+
+  Error readBytes(uint32_t Offset, uint32_t Size,
+                  ArrayRef<uint8_t> &Buffer) override {
+    if (auto EC = checkOffsetForRead(Offset, Size))
+      return EC;
+    Buffer = Data.slice(Offset, Size);
+    return Error::success();
+  }
+
+  Error readLongestContiguousChunk(uint32_t Offset,
+                                   ArrayRef<uint8_t> &Buffer) override {
+    if (auto EC = checkOffsetForRead(Offset, 1))
+      return EC;
+    Buffer = Data.slice(Offset);
+    return Error::success();
+  }
+
+  uint32_t getLength() override { return Data.size(); }
+
+  ArrayRef<uint8_t> data() const { return Data; }
+
+  StringRef str() const {
+    const char *CharData = reinterpret_cast<const char *>(Data.data());
+    return StringRef(CharData, Data.size());
+  }
+
+protected:
+  llvm::support::endianness Endian;
+  ArrayRef<uint8_t> Data;
+};
+
+/// An implementation of BinaryStream whose data is backed by an llvm
+/// MemoryBuffer object.  MemoryBufferByteStream owns the MemoryBuffer in
+/// question.  As with BinaryByteStream, reading from a MemoryBufferByteStream
+/// will never cause a copy.
+class MemoryBufferByteStream : public BinaryByteStream {
+public:
+  MemoryBufferByteStream(std::unique_ptr<MemoryBuffer> Buffer,
+                         llvm::support::endianness Endian)
+      : BinaryByteStream(Buffer->getBuffer(), Endian),
+        MemBuffer(std::move(Buffer)) {}
+
+  std::unique_ptr<MemoryBuffer> MemBuffer;
+};
+
+/// An implementation of BinaryStream which holds its entire data set
+/// in a single contiguous buffer.  As with BinaryByteStream, the mutable
+/// version also guarantees that no read operation will ever incur a copy,
+/// and similarly it does not own the underlying buffer.
+class MutableBinaryByteStream : public WritableBinaryStream {
+public:
+  MutableBinaryByteStream() = default;
+  MutableBinaryByteStream(MutableArrayRef<uint8_t> Data,
+                          llvm::support::endianness Endian)
+      : Data(Data), ImmutableStream(Data, Endian) {}
+
+  llvm::support::endianness getEndian() const override {
+    return ImmutableStream.getEndian();
+  }
+
+  Error readBytes(uint32_t Offset, uint32_t Size,
+                  ArrayRef<uint8_t> &Buffer) override {
+    return ImmutableStream.readBytes(Offset, Size, Buffer);
+  }
+
+  Error readLongestContiguousChunk(uint32_t Offset,
+                                   ArrayRef<uint8_t> &Buffer) override {
+    return ImmutableStream.readLongestContiguousChunk(Offset, Buffer);
+  }
+
+  uint32_t getLength() override { return ImmutableStream.getLength(); }
+
+  Error writeBytes(uint32_t Offset, ArrayRef<uint8_t> Buffer) override {
+    if (Buffer.empty())
+      return Error::success();
+
+    if (auto EC = checkOffsetForWrite(Offset, Buffer.size()))
+      return EC;
+
+    uint8_t *DataPtr = const_cast<uint8_t *>(Data.data());
+    ::memcpy(DataPtr + Offset, Buffer.data(), Buffer.size());
+    return Error::success();
+  }
+
+  Error commit() override { return Error::success(); }
+
+  MutableArrayRef<uint8_t> data() const { return Data; }
+
+private:
+  MutableArrayRef<uint8_t> Data;
+  BinaryByteStream ImmutableStream;
+};
+
+/// An implementation of WritableBinaryStream which can write at its end
+/// causing the underlying data to grow.  This class owns the underlying data.
+class AppendingBinaryByteStream : public WritableBinaryStream {
+  std::vector<uint8_t> Data;
+  llvm::support::endianness Endian = llvm::support::little;
+
+public:
+  AppendingBinaryByteStream() = default;
+  AppendingBinaryByteStream(llvm::support::endianness Endian)
+      : Endian(Endian) {}
+
+  void clear() { Data.clear(); }
+
+  llvm::support::endianness getEndian() const override { return Endian; }
+
+  Error readBytes(uint32_t Offset, uint32_t Size,
+                  ArrayRef<uint8_t> &Buffer) override {
+    if (auto EC = checkOffsetForWrite(Offset, Buffer.size()))
+      return EC;
+
+    Buffer = makeArrayRef(Data).slice(Offset, Size);
+    return Error::success();
+  }
+
+  void insert(uint32_t Offset, ArrayRef<uint8_t> Bytes) {
+    Data.insert(Data.begin() + Offset, Bytes.begin(), Bytes.end());
+  }
+
+  Error readLongestContiguousChunk(uint32_t Offset,
+                                   ArrayRef<uint8_t> &Buffer) override {
+    if (auto EC = checkOffsetForWrite(Offset, 1))
+      return EC;
+
+    Buffer = makeArrayRef(Data).slice(Offset);
+    return Error::success();
+  }
+
+  uint32_t getLength() override { return Data.size(); }
+
+  Error writeBytes(uint32_t Offset, ArrayRef<uint8_t> Buffer) override {
+    if (Buffer.empty())
+      return Error::success();
+
+    // This is well-defined for any case except where offset is strictly
+    // greater than the current length.  If offset is equal to the current
+    // length, we can still grow.  If offset is beyond the current length, we
+    // would have to decide how to deal with the intermediate uninitialized
+    // bytes.  So we punt on that case for simplicity and just say it's an
+    // error.
+    if (Offset > getLength())
+      return make_error<BinaryStreamError>(stream_error_code::invalid_offset);
+
+    uint32_t RequiredSize = Offset + Buffer.size();
+    if (RequiredSize > Data.size())
+      Data.resize(RequiredSize);
+
+    ::memcpy(Data.data() + Offset, Buffer.data(), Buffer.size());
+    return Error::success();
+  }
+
+  Error commit() override { return Error::success(); }
+
+  /// Return the properties of this stream.
+  virtual BinaryStreamFlags getFlags() const override {
+    return BSF_Write | BSF_Append;
+  }
+
+  MutableArrayRef<uint8_t> data() { return Data; }
+};
+
+/// An implementation of WritableBinaryStream backed by an llvm
+/// FileOutputBuffer.
+class FileBufferByteStream : public WritableBinaryStream {
+private:
+  class StreamImpl : public MutableBinaryByteStream {
+  public:
+    StreamImpl(std::unique_ptr<FileOutputBuffer> Buffer,
+               llvm::support::endianness Endian)
+        : MutableBinaryByteStream(
+              MutableArrayRef<uint8_t>(Buffer->getBufferStart(),
+                                       Buffer->getBufferEnd()),
+              Endian),
+          FileBuffer(std::move(Buffer)) {}
+
+    Error commit() override {
+      if (FileBuffer->commit())
+        return make_error<BinaryStreamError>(
+            stream_error_code::filesystem_error);
+      return Error::success();
+    }
+
+    /// Returns a pointer to the start of the buffer.
+    uint8_t *getBufferStart() const { return FileBuffer->getBufferStart(); }
+
+    /// Returns a pointer to the end of the buffer.
+    uint8_t *getBufferEnd() const { return FileBuffer->getBufferEnd(); }
+
+  private:
+    std::unique_ptr<FileOutputBuffer> FileBuffer;
+  };
+
+public:
+  FileBufferByteStream(std::unique_ptr<FileOutputBuffer> Buffer,
+                       llvm::support::endianness Endian)
+      : Impl(std::move(Buffer), Endian) {}
+
+  llvm::support::endianness getEndian() const override {
+    return Impl.getEndian();
+  }
+
+  Error readBytes(uint32_t Offset, uint32_t Size,
+                  ArrayRef<uint8_t> &Buffer) override {
+    return Impl.readBytes(Offset, Size, Buffer);
+  }
+
+  Error readLongestContiguousChunk(uint32_t Offset,
+                                   ArrayRef<uint8_t> &Buffer) override {
+    return Impl.readLongestContiguousChunk(Offset, Buffer);
+  }
+
+  uint32_t getLength() override { return Impl.getLength(); }
+
+  Error writeBytes(uint32_t Offset, ArrayRef<uint8_t> Data) override {
+    return Impl.writeBytes(Offset, Data);
+  }
+
+  Error commit() override { return Impl.commit(); }
+
+  /// Returns a pointer to the start of the buffer.
+  uint8_t *getBufferStart() const { return Impl.getBufferStart(); }
+
+  /// Returns a pointer to the end of the buffer.
+  uint8_t *getBufferEnd() const { return Impl.getBufferEnd(); }
+
+private:
+  StreamImpl Impl;
+};
+
+} // end namespace llvm
+
+#endif // LLVM_SUPPORT_BYTESTREAM_H