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, 159 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/DebugInfo/DWARF/DWARFExpression.h b/third_party/llvm-project/include/llvm/DebugInfo/DWARF/DWARFExpression.h
new file mode 100644
index 000000000..456d9df95
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/DebugInfo/DWARF/DWARFExpression.h
@@ -0,0 +1,159 @@
+//===--- DWARFExpression.h - DWARF Expression handling ----------*- 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_DEBUGINFO_DWARFEXPRESSION_H
+#define LLVM_DEBUGINFO_DWARFEXPRESSION_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/iterator.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/Support/DataExtractor.h"
+
+namespace llvm {
+class DWARFUnit;
+class MCRegisterInfo;
+class raw_ostream;
+
+class DWARFExpression {
+public:
+  class iterator;
+
+  /// This class represents an Operation in the Expression. Each operation can
+  /// have up to 2 oprerands.
+  ///
+  /// An Operation can be in Error state (check with isError()). This
+  /// means that it couldn't be decoded successfully and if it is the
+  /// case, all others fields contain undefined values.
+  class Operation {
+  public:
+    /// Size and signedness of expression operations' operands.
+    enum Encoding : uint8_t {
+      Size1 = 0,
+      Size2 = 1,
+      Size4 = 2,
+      Size8 = 3,
+      SizeLEB = 4,
+      SizeAddr = 5,
+      SizeRefAddr = 6,
+      SizeBlock = 7, ///< Preceding operand contains block size
+      BaseTypeRef = 8,
+      SignBit = 0x80,
+      SignedSize1 = SignBit | Size1,
+      SignedSize2 = SignBit | Size2,
+      SignedSize4 = SignBit | Size4,
+      SignedSize8 = SignBit | Size8,
+      SignedSizeLEB = SignBit | SizeLEB,
+      SizeNA = 0xFF ///< Unused operands get this encoding.
+    };
+
+    enum DwarfVersion : uint8_t {
+      DwarfNA, ///< Serves as a marker for unused entries
+      Dwarf2 = 2,
+      Dwarf3,
+      Dwarf4,
+      Dwarf5
+    };
+
+    /// Description of the encoding of one expression Op.
+    struct Description {
+      DwarfVersion Version; ///< Dwarf version where the Op was introduced.
+      Encoding Op[2];       ///< Encoding for Op operands, or SizeNA.
+
+      Description(DwarfVersion Version = DwarfNA, Encoding Op1 = SizeNA,
+                  Encoding Op2 = SizeNA)
+          : Version(Version) {
+        Op[0] = Op1;
+        Op[1] = Op2;
+      }
+    };
+
+  private:
+    friend class DWARFExpression::iterator;
+    uint8_t Opcode; ///< The Op Opcode, DW_OP_<something>.
+    Description Desc;
+    bool Error;
+    uint64_t EndOffset;
+    uint64_t Operands[2];
+    uint64_t OperandEndOffsets[2];
+
+  public:
+    Description &getDescription() { return Desc; }
+    uint8_t getCode() { return Opcode; }
+    uint64_t getRawOperand(unsigned Idx) { return Operands[Idx]; }
+    uint64_t getOperandEndOffset(unsigned Idx) { return OperandEndOffsets[Idx]; }
+    uint64_t getEndOffset() { return EndOffset; }
+    bool extract(DataExtractor Data, uint16_t Version, uint8_t AddressSize,
+                 uint64_t Offset);
+    bool isError() { return Error; }
+    bool print(raw_ostream &OS, const DWARFExpression *Expr,
+               const MCRegisterInfo *RegInfo, DWARFUnit *U, bool isEH);
+    bool verify(DWARFUnit *U);
+  };
+
+  /// An iterator to go through the expression operations.
+  class iterator
+      : public iterator_facade_base<iterator, std::forward_iterator_tag,
+                                    Operation> {
+    friend class DWARFExpression;
+    const DWARFExpression *Expr;
+    uint64_t Offset;
+    Operation Op;
+    iterator(const DWARFExpression *Expr, uint64_t Offset)
+        : Expr(Expr), Offset(Offset) {
+      Op.Error =
+          Offset >= Expr->Data.getData().size() ||
+          !Op.extract(Expr->Data, Expr->Version, Expr->AddressSize, Offset);
+    }
+
+  public:
+    class Operation &operator++() {
+      Offset = Op.isError() ? Expr->Data.getData().size() : Op.EndOffset;
+      Op.Error =
+          Offset >= Expr->Data.getData().size() ||
+          !Op.extract(Expr->Data, Expr->Version, Expr->AddressSize, Offset);
+      return Op;
+    }
+
+    class Operation &operator*() {
+      return Op;
+    }
+
+    // Comparison operators are provided out of line.
+    friend bool operator==(const iterator &, const iterator &);
+  };
+
+  DWARFExpression(DataExtractor Data, uint16_t Version, uint8_t AddressSize)
+      : Data(Data), Version(Version), AddressSize(AddressSize) {
+    assert(AddressSize == 8 || AddressSize == 4 || AddressSize == 2);
+  }
+
+  iterator begin() const { return iterator(this, 0); }
+  iterator end() const { return iterator(this, Data.getData().size()); }
+
+  void print(raw_ostream &OS, const MCRegisterInfo *RegInfo, DWARFUnit *U,
+             bool IsEH = false) const;
+
+  bool verify(DWARFUnit *U);
+
+private:
+  DataExtractor Data;
+  uint16_t Version;
+  uint8_t AddressSize;
+};
+
+inline bool operator==(const DWARFExpression::iterator &LHS,
+                       const DWARFExpression::iterator &RHS) {
+  return LHS.Expr == RHS.Expr && LHS.Offset == RHS.Offset;
+}
+
+inline bool operator!=(const DWARFExpression::iterator &LHS,
+                       const DWARFExpression::iterator &RHS) {
+  return !(LHS == RHS);
+}
+}
+#endif