[lldb] Support DW_OP_WASM_location in DWARFExpression

JDevlieghere · JDevlieghere · commit a2a7cf5e4bfa · 2025-07-28T11:10:58.000-07:00
Add support for DW_OP_WASM_location in DWARFExpression. This PR rebases #78977 and cleans up the unit test.
diff --git a/lldb/include/lldb/Expression/DWARFExpression.h b/lldb/include/lldb/Expression/DWARFExpression.h
@@ -52,10 +52,10 @@ class DWARFExpression {
     GetVendorDWARFOpcodeSize(const DataExtractor &data,
                              const lldb::offset_t data_offset,
                              const uint8_t op) const = 0;
-    virtual bool ParseVendorDWARFOpcode(uint8_t op,
-                                        const DataExtractor &opcodes,
-                                        lldb::offset_t &offset,
-                                        Stack &stack) const = 0;
+    virtual bool
+    ParseVendorDWARFOpcode(uint8_t op, const DataExtractor &opcodes,
+                           lldb::offset_t &offset, RegisterContext *reg_ctx,
+                           lldb::RegisterKind reg_kind, Stack &stack) const = 0;
 
     Delegate(const Delegate &) = delete;
     Delegate &operator=(const Delegate &) = delete;
@@ -163,6 +163,10 @@ class DWARFExpression {
 
   bool MatchesOperand(StackFrame &frame, const Instruction::Operand &op) const;
 
+  static llvm::Error ReadRegisterValueAsScalar(RegisterContext *reg_ctx,
+                                               lldb::RegisterKind reg_kind,
+                                               uint32_t reg_num, Value &value);
+
 private:
   /// A data extractor capable of reading opcode bytes
   DataExtractor m_data;
diff --git a/lldb/source/Expression/DWARFExpression.cpp b/lldb/source/Expression/DWARFExpression.cpp
@@ -91,9 +91,10 @@ void DWARFExpression::SetRegisterKind(RegisterKind reg_kind) {
   m_reg_kind = reg_kind;
 }
 
-static llvm::Error ReadRegisterValueAsScalar(RegisterContext *reg_ctx,
-                                             lldb::RegisterKind reg_kind,
-                                             uint32_t reg_num, Value &value) {
+llvm::Error
+DWARFExpression::ReadRegisterValueAsScalar(RegisterContext *reg_ctx,
+                                           lldb::RegisterKind reg_kind,
+                                           uint32_t reg_num, Value &value) {
   if (reg_ctx == nullptr)
     return llvm::createStringError("no register context in frame");
 
@@ -2300,9 +2301,40 @@ llvm::Expected<Value> DWARFExpression::Evaluate(
       break;
     }
 
+    case DW_OP_WASM_location: {
+      uint8_t wasm_op = opcodes.GetU8(&offset);
+      uint32_t index;
+
+      /* LLDB doesn't have an address space to represents WebAssembly locals,
+       * globals and operand stacks.
+       * We encode these elements into virtual registers:
+       *   | tag: 2 bits | index: 30 bits |
+       *   where tag is:
+       *    0: Not a WebAssembly ___location
+       *    1: Local
+       *    2: Global
+       *    3: Operand stack value
+       */
+      if (wasm_op == 3) {
+        index = opcodes.GetU32(&offset);
+        wasm_op = 2; // Global
+      } else {
+        index = opcodes.GetULEB128(&offset);
+      }
+
+      reg_num = (((wasm_op + 1) & 0x03) << 30) | (index & 0x3fffffff);
+
+      if (llvm::Error error =
+              ReadRegisterValueAsScalar(reg_ctx, reg_kind, reg_num, tmp))
+        return std::move(error);
+      stack.push_back(tmp);
+      break;
+    }
+
     default:
       if (dwarf_cu) {
-        if (dwarf_cu->ParseVendorDWARFOpcode(op, opcodes, offset, stack)) {
+        if (dwarf_cu->ParseVendorDWARFOpcode(op, opcodes, offset, reg_ctx,
+                                             reg_kind, stack)) {
           break;
         }
       }
diff --git a/lldb/source/Plugins/ObjectFile/wasm/ObjectFileWasm.cpp b/lldb/source/Plugins/ObjectFile/wasm/ObjectFileWasm.cpp
@@ -376,9 +376,13 @@ DataExtractor ObjectFileWasm::ReadImageData(offset_t offset, uint32_t size) {
         DataBufferSP buffer_sp(data_up.release());
         data.SetData(buffer_sp, 0, buffer_sp->GetByteSize());
       }
+    } else if (offset < m_data.GetByteSize()) {
+      size =
+          std::min(static_cast<uint64_t>(size), m_data.GetByteSize() - offset);
+      return DataExtractor(m_data.GetDataStart() + offset, size, GetByteOrder(),
+                           GetAddressByteSize());
     }
   }
-
   data.SetByteOrder(GetByteOrder());
   return data;
 }
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/CMakeLists.txt b/lldb/source/Plugins/SymbolFile/DWARF/CMakeLists.txt
@@ -35,6 +35,7 @@ add_lldb_library(lldbPluginSymbolFileDWARF PLUGIN
   SymbolFileDWARF.cpp
   SymbolFileDWARFDwo.cpp
   SymbolFileDWARFDebugMap.cpp
+  SymbolFileWasm.cpp
   UniqueDWARFASTType.cpp
 
   LINK_COMPONENTS
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
@@ -736,9 +736,11 @@ DWARFUnit::GetVendorDWARFOpcodeSize(const DataExtractor &data,
 
 bool DWARFUnit::ParseVendorDWARFOpcode(uint8_t op, const DataExtractor &opcodes,
                                        lldb::offset_t &offset,
+                                       RegisterContext *reg_ctx,
+                                       lldb::RegisterKind reg_kind,
                                        std::vector<Value> &stack) const {
   return GetSymbolFileDWARF().ParseVendorDWARFOpcode(op, opcodes, offset,
-                                                     stack);
+                                                     reg_ctx, reg_kind, stack);
 }
 
 bool DWARFUnit::ParseDWARFLocationList(
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.h b/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.h
@@ -164,9 +164,11 @@ class DWARFUnit : public DWARFExpression::Delegate, public UserID {
                                           const lldb::offset_t data_offset,
                                           const uint8_t op) const override;
 
-  bool ParseVendorDWARFOpcode(uint8_t op, const DataExtractor &opcodes,
-                              lldb::offset_t &offset,
-                              std::vector<Value> &stack) const override;
+  virtual bool ParseVendorDWARFOpcode(uint8_t op, const DataExtractor &opcodes,
+                                      lldb::offset_t &offset,
+                                      RegisterContext *reg_ctx,
+                                      lldb::RegisterKind reg_kind,
+                                      std::vector<Value> &stack) const override;
 
   bool ParseDWARFLocationList(const DataExtractor &data,
                               DWARFExpressionList &loc_list) const;
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -32,6 +32,7 @@
 
 #include "Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.h"
 #include "Plugins/Language/CPlusPlus/CPlusPlusLanguage.h"
+#include "Plugins/ObjectFile/wasm/ObjectFileWasm.h"
 
 #include "lldb/Host/FileSystem.h"
 #include "lldb/Host/Host.h"
@@ -41,6 +42,7 @@
 
 #include "Plugins/ExpressionParser/Clang/ClangUtil.h"
 #include "Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.h"
+#include "Plugins/SymbolFile/DWARF/SymbolFileWasm.h"
 #include "Plugins/TypeSystem/Clang/TypeSystemClang.h"
 #include "lldb/Symbol/Block.h"
 #include "lldb/Symbol/CompileUnit.h"
@@ -327,6 +329,9 @@ llvm::StringRef SymbolFileDWARF::GetPluginDescriptionStatic() {
 }
 
 SymbolFile *SymbolFileDWARF::CreateInstance(ObjectFileSP objfile_sp) {
+  if (llvm::isa<lldb_private::wasm::ObjectFileWasm>(*objfile_sp))
+    return new SymbolFileWasm(std::move(objfile_sp),
+                              /*dwo_section_list*/ nullptr);
   return new SymbolFileDWARF(std::move(objfile_sp),
                              /*dwo_section_list*/ nullptr);
 }
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
@@ -329,6 +329,8 @@ class SymbolFileDWARF : public SymbolFileCommon {
 
   virtual bool ParseVendorDWARFOpcode(uint8_t op, const DataExtractor &opcodes,
                                       lldb::offset_t &offset,
+                                      RegisterContext *reg_ctx,
+                                      lldb::RegisterKind reg_kind,
                                       std::vector<Value> &stack) const {
     return false;
   }
@@ -556,6 +558,7 @@ class SymbolFileDWARF : public SymbolFileCommon {
   /// an index that identifies the .DWO or .o file.
   std::optional<uint64_t> m_file_index;
 };
+
 } // namespace dwarf
 } // namespace lldb_private::plugin
 
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDwo.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDwo.cpp
@@ -97,9 +97,11 @@ uint64_t SymbolFileDWARFDwo::GetDebugInfoSize(bool load_all_debug_info) {
 }
 
 bool SymbolFileDWARFDwo::ParseVendorDWARFOpcode(
-    uint8_t op, const lldb_private::DataExtractor &opcodes,
-    lldb::offset_t &offset, std::vector<lldb_private::Value> &stack) const {
-  return GetBaseSymbolFile().ParseVendorDWARFOpcode(op, opcodes, offset, stack);
+    uint8_t op, const DataExtractor &opcodes, lldb::offset_t &offset,
+    RegisterContext *reg_ctx, lldb::RegisterKind reg_kind,
+    std::vector<Value> &stack) const {
+  return GetBaseSymbolFile().ParseVendorDWARFOpcode(op, opcodes, offset,
+                                                    reg_ctx, reg_kind, stack);
 }
 
 llvm::DenseMap<const DWARFDebugInfoEntry *, Type *> &
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDwo.h b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDwo.h
@@ -50,7 +50,8 @@ class SymbolFileDWARFDwo : public SymbolFileDWARF {
   uint64_t GetDebugInfoSize(bool load_all_debug_info = false) override;
 
   bool ParseVendorDWARFOpcode(uint8_t op, const DataExtractor &opcodes,
-                              lldb::offset_t &offset,
+                              lldb::offset_t &offset, RegisterContext *reg_ctx,
+                              lldb::RegisterKind reg_kind,
                               std::vector<Value> &stack) const override;
 
   void FindGlobalVariables(ConstString name,
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileWasm.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileWasm.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "SymbolFileWasm.h"
+
+using namespace lldb;
+using namespace lldb_private;
+using namespace lldb_private::plugin::dwarf;
+SymbolFileWasm::SymbolFileWasm(ObjectFileSP objfile_sp,
+                               SectionList *dwo_section_list)
+    : SymbolFileDWARF(objfile_sp, dwo_section_list) {}
+
+SymbolFileWasm::~SymbolFileWasm() = default;
+
+lldb::offset_t
+SymbolFileWasm::GetVendorDWARFOpcodeSize(const DataExtractor &data,
+                                         const lldb::offset_t data_offset,
+                                         const uint8_t op) const {
+  if (op != llvm::dwarf::DW_OP_WASM_location) {
+    return LLDB_INVALID_OFFSET;
+  }
+
+  lldb::offset_t offset = data_offset;
+  uint8_t wasm_op = data.GetU8(&offset);
+  if (wasm_op == 3) {
+    data.GetU32(&offset);
+  } else {
+    data.GetULEB128(&offset);
+  }
+  return offset - data_offset;
+}
+
+bool SymbolFileWasm::ParseVendorDWARFOpcode(uint8_t op,
+                                            const DataExtractor &opcodes,
+                                            lldb::offset_t &offset,
+                                            RegisterContext *reg_ctx,
+                                            lldb::RegisterKind reg_kind,
+                                            std::vector<Value> &stack) const {
+  if (op != llvm::dwarf::DW_OP_WASM_location) {
+    return false;
+  }
+
+  uint8_t wasm_op = opcodes.GetU8(&offset);
+
+  /* LLDB doesn't have an address space to represents WebAssembly locals,
+   * globals and operand stacks.
+   * We encode these elements into virtual registers:
+   *   | tag: 2 bits | index: 30 bits |
+   *   where tag is:
+   *    0: Not a WebAssembly ___location
+   *    1: Local
+   *    2: Global
+   *    3: Operand stack value
+   */
+  uint32_t index;
+  if (wasm_op == 3) {
+    index = opcodes.GetU32(&offset);
+    wasm_op = 2; // Global
+  } else {
+    index = opcodes.GetULEB128(&offset);
+  }
+
+  uint32_t reg_num = (((wasm_op + 1) & 0x03) << 30) | (index & 0x3fffffff);
+
+  Value tmp;
+  llvm::Error error = DWARFExpression::ReadRegisterValueAsScalar(
+      reg_ctx, reg_kind, reg_num, tmp);
+  if (error)
+    return false;
+
+  stack.push_back(tmp);
+  return true;
+}
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileWasm.h b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileWasm.h
@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 LLDB_SOURCE_PLUGINS_SYMBOLFILE_DWARF_SYMBOLFILEWASM_H
+#define LLDB_SOURCE_PLUGINS_SYMBOLFILE_DWARF_SYMBOLFILEWASM_H
+
+#include "SymbolFileDWARF.h"
+
+namespace lldb_private::plugin {
+namespace dwarf {
+class SymbolFileWasm : public SymbolFileDWARF {
+public:
+  SymbolFileWasm(lldb::ObjectFileSP objfile_sp, SectionList *dwo_section_list);
+
+  ~SymbolFileWasm() override;
+
+  lldb::offset_t GetVendorDWARFOpcodeSize(const DataExtractor &data,
+                                          const lldb::offset_t data_offset,
+                                          const uint8_t op) const override;
+
+  bool ParseVendorDWARFOpcode(uint8_t op, const DataExtractor &opcodes,
+                              lldb::offset_t &offset, RegisterContext *reg_ctx,
+                              lldb::RegisterKind reg_kind,
+                              std::vector<Value> &stack) const override;
+};
+} // namespace dwarf
+} // namespace lldb_private::plugin
+
+#endif
diff --git a/lldb/unittests/Expression/CMakeLists.txt b/lldb/unittests/Expression/CMakeLists.txt
@@ -8,6 +8,8 @@ add_lldb_unittest(ExpressionTests
   LINK_LIBS
     lldbCore
     lldbPluginObjectFileELF
+    lldbPluginObjectFileWasm
+    lldbPluginSymbolVendorWasm
     lldbPluginPlatformLinux
     lldbPluginExpressionParserClang
     lldbPluginTypeSystemClang
diff --git a/lldb/unittests/Expression/DWARFExpressionTest.cpp b/lldb/unittests/Expression/DWARFExpressionTest.cpp

Original file line number	Diff line number	Diff line change
`@@ -376,9 +376,13 @@ DataExtractor ObjectFileWasm::ReadImageData(offset_t offset, uint32_t size) {`
`376`	`376`	`DataBufferSP buffer_sp(data_up.release());`
`377`	`377`	`data.SetData(buffer_sp, 0, buffer_sp->GetByteSize());`
`378`	`378`	`}`
	`379`	`+ } else if (offset < m_data.GetByteSize()) {`
	`380`	`+ size =`
	`381`	`+ std::min(static_cast<uint64_t>(size), m_data.GetByteSize() - offset);`
	`382`	`+ return DataExtractor(m_data.GetDataStart() + offset, size, GetByteOrder(),`
	`383`	`+ GetAddressByteSize());`
`379`	`384`	`}`
`380`	`385`	`}`
`381`		`-`
`382`	`386`	`data.SetByteOrder(GetByteOrder());`
`383`	`387`	`return data;`
`384`	`388`	`}`
Original file line number	Diff line number	Diff line change
`@@ -97,9 +97,11 @@ uint64_t SymbolFileDWARFDwo::GetDebugInfoSize(bool load_all_debug_info) {`
`97`	`97`	`}`
`98`	`98`
`99`	`99`	`bool SymbolFileDWARFDwo::ParseVendorDWARFOpcode(`
`100`		`- uint8_t op, const lldb_private::DataExtractor &opcodes,`
`101`		`- lldb::offset_t &offset, std::vector<lldb_private::Value> &stack) const {`
`102`		`- return GetBaseSymbolFile().ParseVendorDWARFOpcode(op, opcodes, offset, stack);`
	`100`	`+ uint8_t op, const DataExtractor &opcodes, lldb::offset_t &offset,`
	`101`	`+ RegisterContext *reg_ctx, lldb::RegisterKind reg_kind,`
	`102`	`+ std::vector<Value> &stack) const {`
	`103`	`+ return GetBaseSymbolFile().ParseVendorDWARFOpcode(op, opcodes, offset,`
	`104`	`+ reg_ctx, reg_kind, stack);`
`103`	`105`	`}`
`104`	`106`
`105`	`107`	`llvm::DenseMap<const DWARFDebugInfoEntry , Type > &`