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, 199 insertions, 0 deletions

diff --git a/third_party/llvm-project/DWARFGdbIndex.cpp b/third_party/llvm-project/DWARFGdbIndex.cpp
new file mode 100644
index 000000000..252b58e5a
--- /dev/null
+++ b/third_party/llvm-project/DWARFGdbIndex.cpp
@@ -0,0 +1,199 @@
+//===- DWARFGdbIndex.cpp --------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/DebugInfo/DWARF/DWARFGdbIndex.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Format.h"
+#include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <cassert>
+#include <cinttypes>
+#include <cstdint>
+#include <utility>
+
+using namespace llvm;
+
+// .gdb_index section format reference:
+// https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html
+
+void DWARFGdbIndex::dumpCUList(raw_ostream &OS) const {
+  OS << format("\n  CU list offset = 0x%x, has %" PRId64 " entries:",
+               CuListOffset, (uint64_t)CuList.size())
+     << '\n';
+  uint32_t I = 0;
+  for (const CompUnitEntry &CU : CuList)
+    OS << format("    %d: Offset = 0x%llx, Length = 0x%llx\n", I++, CU.Offset,
+                 CU.Length);
+}
+
+void DWARFGdbIndex::dumpTUList(raw_ostream &OS) const {
+  OS << formatv("\n  Types CU list offset = {0:x}, has {1} entries:\n",
+                TuListOffset, TuList.size());
+  uint32_t I = 0;
+  for (const TypeUnitEntry &TU : TuList)
+    OS << formatv("    {0}: offset = {1:x8}, type_offset = {2:x8}, "
+                  "type_signature = {3:x16}\n",
+                  I++, TU.Offset, TU.TypeOffset, TU.TypeSignature);
+}
+
+void DWARFGdbIndex::dumpAddressArea(raw_ostream &OS) const {
+  OS << format("\n  Address area offset = 0x%x, has %" PRId64 " entries:",
+               AddressAreaOffset, (uint64_t)AddressArea.size())
+     << '\n';
+  for (const AddressEntry &Addr : AddressArea)
+    OS << format(
+        "    Low/High address = [0x%llx, 0x%llx) (Size: 0x%llx), CU id = %d\n",
+        Addr.LowAddress, Addr.HighAddress, Addr.HighAddress - Addr.LowAddress,
+        Addr.CuIndex);
+}
+
+void DWARFGdbIndex::dumpSymbolTable(raw_ostream &OS) const {
+  OS << format("\n  Symbol table offset = 0x%x, size = %" PRId64
+               ", filled slots:",
+               SymbolTableOffset, (uint64_t)SymbolTable.size())
+     << '\n';
+  uint32_t I = -1;
+  for (const SymTableEntry &E : SymbolTable) {
+    ++I;
+    if (!E.NameOffset && !E.VecOffset)
+      continue;
+
+    OS << format("    %d: Name offset = 0x%x, CU vector offset = 0x%x\n", I,
+                 E.NameOffset, E.VecOffset);
+
+    StringRef Name = ConstantPoolStrings.substr(
+        ConstantPoolOffset - StringPoolOffset + E.NameOffset);
+
+    auto CuVector = std::find_if(
+        ConstantPoolVectors.begin(), ConstantPoolVectors.end(),
+        [&](const std::pair<uint32_t, SmallVector<uint32_t, 0>> &V) {
+          return V.first == E.VecOffset;
+        });
+    assert(CuVector != ConstantPoolVectors.end() && "Invalid symbol table");
+    uint32_t CuVectorId = CuVector - ConstantPoolVectors.begin();
+    OS << format("      String name: %s, CU vector index: %d\n", Name.data(),
+                 CuVectorId);
+  }
+}
+
+void DWARFGdbIndex::dumpConstantPool(raw_ostream &OS) const {
+  OS << format("\n  Constant pool offset = 0x%x, has %" PRId64 " CU vectors:",
+               ConstantPoolOffset, (uint64_t)ConstantPoolVectors.size());
+  uint32_t I = 0;
+  for (const auto &V : ConstantPoolVectors) {
+    OS << format("\n    %d(0x%x): ", I++, V.first);
+    for (uint32_t Val : V.second)
+      OS << format("0x%x ", Val);
+  }
+  OS << '\n';
+}
+
+void DWARFGdbIndex::dump(raw_ostream &OS) {
+  if (HasError) {
+    OS << "\n<error parsing>\n";
+    return;
+  }
+
+  if (HasContent) {
+    OS << "  Version = " << Version << '\n';
+    dumpCUList(OS);
+    dumpTUList(OS);
+    dumpAddressArea(OS);
+    dumpSymbolTable(OS);
+    dumpConstantPool(OS);
+  }
+}
+
+bool DWARFGdbIndex::parseImpl(DataExtractor Data) {
+  uint64_t Offset = 0;
+
+  // Only version 7 is supported at this moment.
+  Version = Data.getU32(&Offset);
+  if (Version != 7)
+    return false;
+
+  CuListOffset = Data.getU32(&Offset);
+  TuListOffset = Data.getU32(&Offset);
+  AddressAreaOffset = Data.getU32(&Offset);
+  SymbolTableOffset = Data.getU32(&Offset);
+  ConstantPoolOffset = Data.getU32(&Offset);
+
+  if (Offset != CuListOffset)
+    return false;
+
+  uint32_t CuListSize = (TuListOffset - CuListOffset) / 16;
+  CuList.reserve(CuListSize);
+  for (uint32_t i = 0; i < CuListSize; ++i) {
+    uint64_t CuOffset = Data.getU64(&Offset);
+    uint64_t CuLength = Data.getU64(&Offset);
+    CuList.push_back({CuOffset, CuLength});
+  }
+
+  // CU Types are no longer needed as DWARF skeleton type units never made it
+  // into the standard.
+  uint32_t TuListSize = (AddressAreaOffset - TuListOffset) / 24;
+  TuList.resize(TuListSize);
+  for (uint32_t I = 0; I < TuListSize; ++I) {
+    uint64_t CuOffset = Data.getU64(&Offset);
+    uint64_t TypeOffset = Data.getU64(&Offset);
+    uint64_t Signature = Data.getU64(&Offset);
+    TuList[I] = {CuOffset, TypeOffset, Signature};
+  }
+
+  uint32_t AddressAreaSize = (SymbolTableOffset - AddressAreaOffset) / 20;
+  AddressArea.reserve(AddressAreaSize);
+  for (uint32_t i = 0; i < AddressAreaSize; ++i) {
+    uint64_t LowAddress = Data.getU64(&Offset);
+    uint64_t HighAddress = Data.getU64(&Offset);
+    uint32_t CuIndex = Data.getU32(&Offset);
+    AddressArea.push_back({LowAddress, HighAddress, CuIndex});
+  }
+
+  // The symbol table. This is an open addressed hash table. The size of the
+  // hash table is always a power of 2.
+  // Each slot in the hash table consists of a pair of offset_type values. The
+  // first value is the offset of the symbol's name in the constant pool. The
+  // second value is the offset of the CU vector in the constant pool.
+  // If both values are 0, then this slot in the hash table is empty. This is ok
+  // because while 0 is a valid constant pool index, it cannot be a valid index
+  // for both a string and a CU vector.
+  uint32_t SymTableSize = (ConstantPoolOffset - SymbolTableOffset) / 8;
+  SymbolTable.reserve(SymTableSize);
+  uint32_t CuVectorsTotal = 0;
+  for (uint32_t i = 0; i < SymTableSize; ++i) {
+    uint32_t NameOffset = Data.getU32(&Offset);
+    uint32_t CuVecOffset = Data.getU32(&Offset);
+    SymbolTable.push_back({NameOffset, CuVecOffset});
+    if (NameOffset || CuVecOffset)
+      ++CuVectorsTotal;
+  }
+
+  // The constant pool. CU vectors are stored first, followed by strings.
+  // The first value is the number of CU indices in the vector. Each subsequent
+  // value is the index and symbol attributes of a CU in the CU list.
+  for (uint32_t i = 0; i < CuVectorsTotal; ++i) {
+    ConstantPoolVectors.emplace_back(0, SmallVector<uint32_t, 0>());
+    auto &Vec = ConstantPoolVectors.back();
+    Vec.first = Offset - ConstantPoolOffset;
+
+    uint32_t Num = Data.getU32(&Offset);
+    for (uint32_t j = 0; j < Num; ++j)
+      Vec.second.push_back(Data.getU32(&Offset));
+  }
+
+  ConstantPoolStrings = Data.getData().drop_front(Offset);
+  StringPoolOffset = Offset;
+  return true;
+}
+
+void DWARFGdbIndex::parse(DataExtractor Data) {
+  HasContent = !Data.getData().empty();
+  HasError = HasContent && !parseImpl(Data);
+}