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, 202 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/MC/MCFixup.h b/third_party/llvm-project/include/llvm/MC/MCFixup.h
new file mode 100644
index 000000000..29e321e23
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/MC/MCFixup.h
@@ -0,0 +1,202 @@
+//===-- llvm/MC/MCFixup.h - Instruction Relocation and Patching -*- 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_MC_MCFIXUP_H
+#define LLVM_MC_MCFIXUP_H
+
+#include "llvm/MC/MCExpr.h"
+#include "llvm/Support/DataTypes.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/SMLoc.h"
+#include <cassert>
+
+namespace llvm {
+class MCExpr;
+
+/// Extensible enumeration to represent the type of a fixup.
+enum MCFixupKind {
+  FK_NONE = 0,    ///< A no-op fixup.
+  FK_Data_1,      ///< A one-byte fixup.
+  FK_Data_2,      ///< A two-byte fixup.
+  FK_Data_4,      ///< A four-byte fixup.
+  FK_Data_8,      ///< A eight-byte fixup.
+  FK_Data_6b,     ///< A six-bits fixup.
+  FK_PCRel_1,     ///< A one-byte pc relative fixup.
+  FK_PCRel_2,     ///< A two-byte pc relative fixup.
+  FK_PCRel_4,     ///< A four-byte pc relative fixup.
+  FK_PCRel_8,     ///< A eight-byte pc relative fixup.
+  FK_GPRel_1,     ///< A one-byte gp relative fixup.
+  FK_GPRel_2,     ///< A two-byte gp relative fixup.
+  FK_GPRel_4,     ///< A four-byte gp relative fixup.
+  FK_GPRel_8,     ///< A eight-byte gp relative fixup.
+  FK_DTPRel_4,    ///< A four-byte dtp relative fixup.
+  FK_DTPRel_8,    ///< A eight-byte dtp relative fixup.
+  FK_TPRel_4,     ///< A four-byte tp relative fixup.
+  FK_TPRel_8,     ///< A eight-byte tp relative fixup.
+  FK_SecRel_1,    ///< A one-byte section relative fixup.
+  FK_SecRel_2,    ///< A two-byte section relative fixup.
+  FK_SecRel_4,    ///< A four-byte section relative fixup.
+  FK_SecRel_8,    ///< A eight-byte section relative fixup.
+  FK_Data_Add_1,  ///< A one-byte add fixup.
+  FK_Data_Add_2,  ///< A two-byte add fixup.
+  FK_Data_Add_4,  ///< A four-byte add fixup.
+  FK_Data_Add_8,  ///< A eight-byte add fixup.
+  FK_Data_Add_6b, ///< A six-bits add fixup.
+  FK_Data_Sub_1,  ///< A one-byte sub fixup.
+  FK_Data_Sub_2,  ///< A two-byte sub fixup.
+  FK_Data_Sub_4,  ///< A four-byte sub fixup.
+  FK_Data_Sub_8,  ///< A eight-byte sub fixup.
+  FK_Data_Sub_6b, ///< A six-bits sub fixup.
+
+  FirstTargetFixupKind = 128,
+
+  // Limit range of target fixups, in case we want to pack more efficiently
+  // later.
+  MaxTargetFixupKind = (1 << 8)
+};
+
+/// Encode information on a single operation to perform on a byte
+/// sequence (e.g., an encoded instruction) which requires assemble- or run-
+/// time patching.
+///
+/// Fixups are used any time the target instruction encoder needs to represent
+/// some value in an instruction which is not yet concrete. The encoder will
+/// encode the instruction assuming the value is 0, and emit a fixup which
+/// communicates to the assembler backend how it should rewrite the encoded
+/// value.
+///
+/// During the process of relaxation, the assembler will apply fixups as
+/// symbolic values become concrete. When relaxation is complete, any remaining
+/// fixups become relocations in the object file (or errors, if the fixup cannot
+/// be encoded on the target).
+class MCFixup {
+  /// The value to put into the fixup location. The exact interpretation of the
+  /// expression is target dependent, usually it will be one of the operands to
+  /// an instruction or an assembler directive.
+  const MCExpr *Value = nullptr;
+
+  /// The byte index of start of the relocation inside the MCFragment.
+  uint32_t Offset = 0;
+
+  /// The target dependent kind of fixup item this is. The kind is used to
+  /// determine how the operand value should be encoded into the instruction.
+  MCFixupKind Kind = FK_NONE;
+
+  /// The source location which gave rise to the fixup, if any.
+  SMLoc Loc;
+public:
+  static MCFixup create(uint32_t Offset, const MCExpr *Value,
+                        MCFixupKind Kind, SMLoc Loc = SMLoc()) {
+    assert(Kind < MaxTargetFixupKind && "Kind out of range!");
+    MCFixup FI;
+    FI.Value = Value;
+    FI.Offset = Offset;
+    FI.Kind = Kind;
+    FI.Loc = Loc;
+    return FI;
+  }
+
+  /// Return a fixup corresponding to the add half of a add/sub fixup pair for
+  /// the given Fixup.
+  static MCFixup createAddFor(const MCFixup &Fixup) {
+    MCFixup FI;
+    FI.Value = Fixup.getValue();
+    FI.Offset = Fixup.getOffset();
+    FI.Kind = getAddKindForKind(Fixup.getKind());
+    FI.Loc = Fixup.getLoc();
+    return FI;
+  }
+
+  /// Return a fixup corresponding to the sub half of a add/sub fixup pair for
+  /// the given Fixup.
+  static MCFixup createSubFor(const MCFixup &Fixup) {
+    MCFixup FI;
+    FI.Value = Fixup.getValue();
+    FI.Offset = Fixup.getOffset();
+    FI.Kind = getSubKindForKind(Fixup.getKind());
+    FI.Loc = Fixup.getLoc();
+    return FI;
+  }
+
+  MCFixupKind getKind() const { return Kind; }
+
+  unsigned getTargetKind() const { return Kind; }
+
+  uint32_t getOffset() const { return Offset; }
+  void setOffset(uint32_t Value) { Offset = Value; }
+
+  const MCExpr *getValue() const { return Value; }
+
+  /// Return the generic fixup kind for a value with the given size. It
+  /// is an error to pass an unsupported size.
+  static MCFixupKind getKindForSize(unsigned Size, bool IsPCRel) {
+    switch (Size) {
+    default: llvm_unreachable("Invalid generic fixup size!");
+    case 1:
+      return IsPCRel ? FK_PCRel_1 : FK_Data_1;
+    case 2:
+      return IsPCRel ? FK_PCRel_2 : FK_Data_2;
+    case 4:
+      return IsPCRel ? FK_PCRel_4 : FK_Data_4;
+    case 8:
+      return IsPCRel ? FK_PCRel_8 : FK_Data_8;
+    }
+  }
+
+  /// Return the generic fixup kind for a value with the given size in bits.
+  /// It is an error to pass an unsupported size.
+  static MCFixupKind getKindForSizeInBits(unsigned Size, bool IsPCRel) {
+    switch (Size) {
+    default:
+      llvm_unreachable("Invalid generic fixup size!");
+    case 6:
+      assert(!IsPCRel && "Invalid pc-relative fixup size!");
+      return FK_Data_6b;
+    case 8:
+      return IsPCRel ? FK_PCRel_1 : FK_Data_1;
+    case 16:
+      return IsPCRel ? FK_PCRel_2 : FK_Data_2;
+    case 32:
+      return IsPCRel ? FK_PCRel_4 : FK_Data_4;
+    case 64:
+      return IsPCRel ? FK_PCRel_8 : FK_Data_8;
+    }
+  }
+
+  /// Return the generic fixup kind for an addition with a given size. It
+  /// is an error to pass an unsupported size.
+  static MCFixupKind getAddKindForKind(MCFixupKind Kind) {
+    switch (Kind) {
+    default: llvm_unreachable("Unknown type to convert!");
+    case FK_Data_1: return FK_Data_Add_1;
+    case FK_Data_2: return FK_Data_Add_2;
+    case FK_Data_4: return FK_Data_Add_4;
+    case FK_Data_8: return FK_Data_Add_8;
+    case FK_Data_6b: return FK_Data_Add_6b;
+    }
+  }
+
+  /// Return the generic fixup kind for an subtraction with a given size. It
+  /// is an error to pass an unsupported size.
+  static MCFixupKind getSubKindForKind(MCFixupKind Kind) {
+    switch (Kind) {
+    default: llvm_unreachable("Unknown type to convert!");
+    case FK_Data_1: return FK_Data_Sub_1;
+    case FK_Data_2: return FK_Data_Sub_2;
+    case FK_Data_4: return FK_Data_Sub_4;
+    case FK_Data_8: return FK_Data_Sub_8;
+    case FK_Data_6b: return FK_Data_Sub_6b;
+    }
+  }
+
+  SMLoc getLoc() const { return Loc; }
+};
+
+} // End llvm namespace
+
+#endif