[Lldb-commits] [lldb] Add the ability to get a C++ vtable ValueObject from another ValueObj… (PR #67599)

[Greg Clayton via lldb-commits]

================
@@ -0,0 +1,325 @@
+//===-- ValueObjectVTable.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 "lldb/Core/ValueObjectVTable.h"
+#include "lldb/Core/Module.h"
+#include "lldb/Core/ValueObjectChild.h"
+#include "lldb/Symbol/Function.h"
+#include "lldb/lldb-defines.h"
+#include "lldb/lldb-enumerations.h"
+#include "lldb/lldb-forward.h"
+#include "lldb/lldb-private-enumerations.h"
+#include "clang/Tooling/Transformer/RangeSelector.h"
+#include "llvm/Support/MathExtras.h"
+#include <cstdint>
+
+using namespace lldb;
+using namespace lldb_private;
+
+class ValueObjectVTableChild : public ValueObject {
+public:
+  ValueObjectVTableChild(ValueObject &parent, uint32_t func_idx,
+                         uint64_t addr_size)
+      : ValueObject(parent), m_func_idx(func_idx), m_addr_size(addr_size) {
+    SetFormat(eFormatPointer);
+    SetName(ConstString(llvm::formatv("[{0}]", func_idx).str()));
+  }
+
+  ~ValueObjectVTableChild() override = default;
+
+  std::optional<uint64_t> GetByteSize() override { return m_addr_size; };
+
+  size_t CalculateNumChildren(uint32_t max) override { return 0; };
+
+  ValueType GetValueType() const override { return eValueTypeVTableEntry; };
+
+  bool IsInScope() override {
+    ValueObject *parent = GetParent();
+    if (parent)
+      return parent->IsInScope();
+    return false;
+  };
+
+protected:
+  bool UpdateValue() override {
+    SetValueIsValid(false);
+    m_value.Clear();
+    ValueObject *parent = GetParent();
+    if (!parent) {
+      m_error.SetErrorString("no parent object");
+      return false;
+    }
+
+    addr_t parent_addr = parent->GetValueAsUnsigned(LLDB_INVALID_ADDRESS);
+    if (parent_addr == LLDB_INVALID_ADDRESS) {
+      m_error.SetErrorString("parent has invalid address");
+      return false;
+    }
+
+    ProcessSP process_sp = GetProcessSP();
+    if (!process_sp) {
+      m_error.SetErrorString("no process");
+      return false;
+    }
+
+    TargetSP target_sp = GetTargetSP();
+    if (!target_sp) {
+      m_error.SetErrorString("no target");
+      return false;
+    }
+
+    // Each `vtable_entry_addr` points to the function pointer.
+    addr_t vtable_entry_addr = parent_addr + m_func_idx * m_addr_size;
+    addr_t vfunc_ptr =
+        process_sp->ReadPointerFromMemory(vtable_entry_addr, m_error);
+    if (m_error.Fail()) {
+      m_error.SetErrorStringWithFormat(
+          "failed to read virtual function entry 0x%16.16" PRIx64,
+          vtable_entry_addr);
+      return false;
+    }
+
+    Address resolved_vfunc_ptr_address;
+    target_sp->ResolveLoadAddress(vfunc_ptr, resolved_vfunc_ptr_address);
+    if (!resolved_vfunc_ptr_address.IsValid()) {
+      m_error.SetErrorStringWithFormat(
+          "unable to resolve func ptr address: 0x%16.16" PRIx64, vfunc_ptr);
+      return false;
+    }
----------------
clayborg wrote:

Yes, good idea here. We are reading individual function pointers here, so we should still show it. This could also be JIT'ed code where we might not have a section for the address. This would be hard to test since these function pointers are in read only memory. Can you think of a way to test this? We won't get a child like this unless the parent's vtable pointer resolved to a "vtable for <classname>" symbol, so I am not sure how to test. I guess we can use our debugger superpowers to ruin the vtable pointer and test that way.

https://github.com/llvm/llvm-project/pull/67599