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, 122 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Support/MD5.h b/third_party/llvm-project/include/llvm/Support/MD5.h
new file mode 100644
index 000000000..bb2bdbf1b
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Support/MD5.h
@@ -0,0 +1,122 @@
+/* -*- C++ -*-
+ * This code is derived from (original license follows):
+ *
+ * This is an OpenSSL-compatible implementation of the RSA Data Security, Inc.
+ * MD5 Message-Digest Algorithm (RFC 1321).
+ *
+ * Homepage:
+ * http://openwall.info/wiki/people/solar/software/public-domain-source-code/md5
+ *
+ * Author:
+ * Alexander Peslyak, better known as Solar Designer <solar at openwall.com>
+ *
+ * This software was written by Alexander Peslyak in 2001.  No copyright is
+ * claimed, and the software is hereby placed in the public domain.
+ * In case this attempt to disclaim copyright and place the software in the
+ * public domain is deemed null and void, then the software is
+ * Copyright (c) 2001 Alexander Peslyak and it is hereby released to the
+ * general public under the following terms:
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted.
+ *
+ * There's ABSOLUTELY NO WARRANTY, express or implied.
+ *
+ * See md5.c for more information.
+ */
+
+#ifndef LLVM_SUPPORT_MD5_H
+#define LLVM_SUPPORT_MD5_H
+
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Endian.h"
+#include <array>
+#include <cstdint>
+
+namespace llvm {
+
+template <typename T> class ArrayRef;
+
+class MD5 {
+  // Any 32-bit or wider unsigned integer data type will do.
+  typedef uint32_t MD5_u32plus;
+
+  MD5_u32plus a = 0x67452301;
+  MD5_u32plus b = 0xefcdab89;
+  MD5_u32plus c = 0x98badcfe;
+  MD5_u32plus d = 0x10325476;
+  MD5_u32plus hi = 0;
+  MD5_u32plus lo = 0;
+  uint8_t buffer[64];
+  MD5_u32plus block[16];
+
+public:
+  struct MD5Result {
+    std::array<uint8_t, 16> Bytes;
+
+    operator std::array<uint8_t, 16>() const { return Bytes; }
+
+    const uint8_t &operator[](size_t I) const { return Bytes[I]; }
+    uint8_t &operator[](size_t I) { return Bytes[I]; }
+
+    SmallString<32> digest() const;
+
+    uint64_t low() const {
+      // Our MD5 implementation returns the result in little endian, so the low
+      // word is first.
+      using namespace support;
+      return endian::read<uint64_t, little, unaligned>(Bytes.data());
+    }
+
+    uint64_t high() const {
+      using namespace support;
+      return endian::read<uint64_t, little, unaligned>(Bytes.data() + 8);
+    }
+    std::pair<uint64_t, uint64_t> words() const {
+      using namespace support;
+      return std::make_pair(high(), low());
+    }
+  };
+
+  MD5();
+
+  /// Updates the hash for the byte stream provided.
+  void update(ArrayRef<uint8_t> Data);
+
+  /// Updates the hash for the StringRef provided.
+  void update(StringRef Str);
+
+  /// Finishes off the hash and puts the result in result.
+  void final(MD5Result &Result);
+
+  /// Translates the bytes in \p Res to a hex string that is
+  /// deposited into \p Str. The result will be of length 32.
+  static void stringifyResult(MD5Result &Result, SmallString<32> &Str);
+
+  /// Computes the hash for a given bytes.
+  static std::array<uint8_t, 16> hash(ArrayRef<uint8_t> Data);
+
+private:
+  const uint8_t *body(ArrayRef<uint8_t> Data);
+};
+
+inline bool operator==(const MD5::MD5Result &LHS, const MD5::MD5Result &RHS) {
+  return LHS.Bytes == RHS.Bytes;
+}
+
+/// Helper to compute and return lower 64 bits of the given string's MD5 hash.
+inline uint64_t MD5Hash(StringRef Str) {
+  using namespace support;
+
+  MD5 Hash;
+  Hash.update(Str);
+  MD5::MD5Result Result;
+  Hash.final(Result);
+  // Return the least significant word.
+  return Result.low();
+}
+
+} // end namespace llvm
+
+#endif // LLVM_SUPPORT_MD5_H