[DWARF] Expose raw bytes in DWARFExpression

This information is necessary for clients of DebugInfo that
do not want to process a DWARF expression, but just treat it as a blob
of data. In BOLT, for example, we need to read these expressions in
CFIs and write them back to the binary, unchanged, so having access to
the original expression encoding is a shortcut to avoid the need to
re-encode the entire expression when re-writing exception handling
info (CFIs).

This patch is an alternative to https://reviews.llvm.org/D98301, in
which we implement the support to re-encode these expressions. But
since we don't really need to change anything in these expressions,
we can just copy their bytes.

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D107515

llvm/include/llvm/DebugInfo/DWARF/DWARFExpression.h

@@ -159,6 +159,8 @@ public:
 
   bool operator==(const DWARFExpression &RHS) const;
 
+  StringRef getData() const { return Data.getData(); }
+
 private:
   DataExtractor Data;
   uint8_t AddressSize;

llvm/unittests/DebugInfo/DWARF/CMakeLists.txt

@@ -20,6 +20,7 @@ add_llvm_unittest(DebugInfoDWARFTests
   DWARFDebugLineTest.cpp
   DWARFDieTest.cpp
   DWARFDieManualExtractTest.cpp
+  DWARFExpressionCopyBytesTest.cpp
   DWARFExpressionCompactPrinterTest.cpp
   DWARFFormValueTest.cpp
   DWARFListTableTest.cpp

llvm/unittests/DebugInfo/DWARF/DWARFExpressionCopyBytesTest.cpp

@@ -0,0 +1,241 @@
+//===- llvm/unittest/DebugInfo/DWARFExpressionRawDataTest.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/ADT/ArrayRef.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/BinaryFormat/Dwarf.h"
+#include "llvm/DebugInfo/DWARF/DWARFContext.h"
+#include "llvm/DebugInfo/DWARF/DWARFDebugFrame.h"
+#include "llvm/DebugInfo/DWARF/DWARFDie.h"
+#include "llvm/DebugInfo/DWARF/DWARFExpression.h"
+#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/MC/MCTargetOptions.h"
+#include "llvm/Object/Binary.h"
+#include "llvm/Support/DataExtractor.h"
+#include "llvm/Support/LEB128.h"
+#include "llvm/Support/TargetRegistry.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Testing/Support/Error.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace dwarf;
+
+namespace {
+
+/// Tests that a client of DebugInfo/DWARF is able to read raw data bytes of a
+/// DWARFExpression parsed from CFI with the intent of writing them back as is
+/// via MC layer / cfi_escape.
+/// This is relevant for binary tools that need to rewrite/copy unwind and
+/// debug info from input to output binary.
+class DWARFExpressionCopyBytesTest : public ::testing::Test {
+public:
+  const char *TripleName = "x86_64-pc-linux";
+  std::unique_ptr<MCRegisterInfo> MRI;
+  std::unique_ptr<MCAsmInfo> MAI;
+  std::unique_ptr<const MCSubtargetInfo> STI;
+  const Target *TheTarget;
+
+  DWARFExpressionCopyBytesTest() {
+    InitializeAllTargets();
+    InitializeAllTargetMCs();
+    InitializeAllAsmPrinters();
+
+    std::string ErrorStr;
+    TheTarget = TargetRegistry::lookupTarget(TripleName, ErrorStr);
+    if (!TheTarget)
+      return;
+
+    MRI.reset(TheTarget->createMCRegInfo(TripleName));
+    MAI.reset(TheTarget->createMCAsmInfo(*MRI, TripleName, MCTargetOptions()));
+    STI.reset(TheTarget->createMCSubtargetInfo(TripleName, "", ""));
+  }
+
+  struct StreamerContext {
+    std::unique_ptr<MCObjectFileInfo> MOFI;
+    std::unique_ptr<MCContext> Ctx;
+    std::unique_ptr<const MCInstrInfo> MII;
+    std::unique_ptr<MCStreamer> Streamer;
+  };
+
+  /// Create all data structures necessary to operate an assembler
+  StreamerContext createStreamer(raw_pwrite_stream &OS);
+  /// Emit a dummy obj file with a single CFI instruction,
+  /// DW_CFA_def_cfa_expression, encoding as its operand the DWARF expression
+  /// represented by ExprBytes
+  SmallString<0> emitObjFile(StringRef ExprBytes);
+  /// Peruse the object file looking for the encoded DWARF expression, and check
+  /// that its operand was encoded correctly
+  void parseCFIsAndCheckExpression(const llvm::object::ObjectFile &E,
+                                   ArrayRef<uint8_t> Expected);
+  /// Open the in-memory relocatable object file and verify that it contains
+  /// the expected DWARF expression bytes
+  void readAndCheckObjFile(StringRef ObjFileData, ArrayRef<uint8_t> Expected);
+  /// Run this test on the DWARF expression represented by the bytes in
+  /// ExprData. Check that the getData() API retrieves these original bytes and
+  /// that we can use them to encode a CFI with those bytes as operands (via
+  /// cfi_escape).
+  void testExpr(ArrayRef<uint8_t> ExprData);
+};
+
+} // namespace
+
+DWARFExpressionCopyBytesTest::StreamerContext
+DWARFExpressionCopyBytesTest::createStreamer(raw_pwrite_stream &OS) {
+  StreamerContext Res;
+  Res.Ctx =
+      std::make_unique<MCContext>(Triple(TripleName), MAI.get(), MRI.get(),
+                                  /*MSTI=*/nullptr);
+  Res.MOFI.reset(TheTarget->createMCObjectFileInfo(*Res.Ctx.get(),
+                                                   /*PIC=*/false));
+  Res.Ctx->setObjectFileInfo(Res.MOFI.get());
+
+  Res.MII.reset(TheTarget->createMCInstrInfo());
+  MCCodeEmitter *MCE = TheTarget->createMCCodeEmitter(*Res.MII, *MRI, *Res.Ctx);
+  MCAsmBackend *MAB =
+      TheTarget->createMCAsmBackend(*STI, *MRI, MCTargetOptions());
+  std::unique_ptr<MCObjectWriter> OW = MAB->createObjectWriter(OS);
+  Res.Streamer.reset(TheTarget->createMCObjectStreamer(
+      Triple(TripleName), *Res.Ctx, std::unique_ptr<MCAsmBackend>(MAB),
+      std::move(OW), std::unique_ptr<MCCodeEmitter>(MCE), *STI,
+      /* RelaxAll */ false,
+      /* IncrementalLinkerCompatible */ false,
+      /* DWARFMustBeAtTheEnd */ false));
+  return Res;
+}
+
+SmallString<0> DWARFExpressionCopyBytesTest::emitObjFile(StringRef ExprBytes) {
+  auto EncodeDefCfaExpr = [&](StringRef Bytes) {
+    std::string Str;
+    raw_string_ostream OS(Str);
+    OS << static_cast<uint8_t>(dwarf::DW_CFA_def_cfa_expression);
+    encodeULEB128(Bytes.size(), OS);
+    OS << Bytes;
+    return Str;
+  };
+
+  SmallString<0> Storage;
+  raw_svector_ostream VecOS(Storage);
+  StreamerContext C = createStreamer(VecOS);
+  C.Streamer->InitSections(false);
+  MCSection *Section = C.MOFI->getTextSection();
+  Section->setHasInstructions(true);
+  C.Streamer->SwitchSection(Section);
+  C.Streamer->emitCFIStartProc(true);
+  auto Str = EncodeDefCfaExpr(ExprBytes);
+  C.Streamer->emitCFIEscape(Str);
+  C.Streamer->emitNops(4, 1, SMLoc());
+  C.Streamer->emitCFIEndProc();
+  C.Streamer->Finish();
+  return Storage;
+}
+
+void DWARFExpressionCopyBytesTest::parseCFIsAndCheckExpression(
+    const llvm::object::ObjectFile &E, ArrayRef<uint8_t> Expected) {
+  auto FetchFirstCfaExpression =
+      [](const DWARFDebugFrame &EHFrame) -> Optional<CFIProgram::Instruction> {
+    for (const dwarf::FrameEntry &Entry : EHFrame.entries()) {
+      const auto *CurFDE = dyn_cast<dwarf::FDE>(&Entry);
+      if (!CurFDE)
+        continue;
+      for (const CFIProgram::Instruction &Instr : CurFDE->cfis()) {
+        if (Instr.Opcode != dwarf::DW_CFA_def_cfa_expression)
+          continue;
+        return Instr;
+      }
+    }
+    return NoneType();
+  };
+
+  std::unique_ptr<DWARFContext> Ctx = DWARFContext::create(E);
+  const DWARFDebugFrame *EHFrame = cantFail(Ctx->getEHFrame());
+  ASSERT_NE(nullptr, EHFrame);
+  auto CfiInstr = FetchFirstCfaExpression(*EHFrame);
+  ASSERT_TRUE(CfiInstr);
+  DWARFExpression Expr = *(CfiInstr->Expression);
+  StringRef ExprData = Expr.getData();
+  EXPECT_EQ(ExprData.size(), Expected.size());
+  for (unsigned I = 0, E = ExprData.size(); I != E; ++I) {
+    EXPECT_EQ(static_cast<uint8_t>(ExprData[I]), Expected[I]);
+  }
+}
+
+void DWARFExpressionCopyBytesTest::readAndCheckObjFile(
+    StringRef ObjFileData, ArrayRef<uint8_t> Expected) {
+  std::unique_ptr<MemoryBuffer> MB =
+      MemoryBuffer::getMemBuffer(ObjFileData, "", false);
+  std::unique_ptr<object::Binary> Bin =
+      cantFail(llvm::object::createBinary(MB->getMemBufferRef()));
+  if (auto *E = dyn_cast<llvm::object::ELFObjectFileBase>(&*Bin)) {
+    parseCFIsAndCheckExpression(*E, Expected);
+  }
+}
+
+void DWARFExpressionCopyBytesTest::testExpr(ArrayRef<uint8_t> ExprData) {
+  // If we didn't build x86, do not run the test.
+  if (!MRI)
+    return;
+
+  DataExtractor DE(ExprData, true, 8);
+  DWARFExpression Expr(DE, 8);
+
+  // Copy this expression into the CFI of a binary and check that we are able to
+  // get it back correctly from this binary.
+  const SmallString<0> EmittedBinContents = emitObjFile(Expr.getData());
+  readAndCheckObjFile(EmittedBinContents.str(), ExprData);
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_reg0) { testExpr({DW_OP_reg0}); }
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_reg10) { testExpr({DW_OP_reg10}); }
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_regx) {
+  testExpr({DW_OP_regx, 0x80, 0x02});
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_breg0) {
+  testExpr({DW_OP_breg0, 0x04});
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_breg0_large_offset) {
+  testExpr({DW_OP_breg0, 0x80, 0x02});
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_breg13) {
+  testExpr({DW_OP_breg13, 0x10});
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_breg13_zero_offset) {
+  testExpr({DW_OP_breg13, 0x00});
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_breg0_negative) {
+  testExpr({DW_OP_breg0, 0x70});
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_bregx) {
+  testExpr({DW_OP_bregx, 0x0d, 0x28});
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_stack_value) {
+  testExpr({DW_OP_breg13, 0x04, DW_OP_stack_value});
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_entry_value) {
+  testExpr({DW_OP_entry_value, 0x01, DW_OP_reg0, DW_OP_stack_value});
+}
+
+TEST_F(DWARFExpressionCopyBytesTest, Test_OP_entry_value_mem) {
+  testExpr({DW_OP_entry_value, 0x02, DW_OP_breg13, 0x10, DW_OP_stack_value});
+}