[lldb] Add VirtualDataExtractor abstraction

Author: JDevlieghere

lldb/include/lldb/Utility/DataExtractor.h

@@ -334,7 +334,8 @@ class DataExtractor {
   /// \return
   ///     A pointer to the bytes in this object's data if the offset
   ///     and length are valid, or nullptr otherwise.
-  const void *GetData(lldb::offset_t *offset_ptr, lldb::offset_t length) const {
+  virtual const void *GetData(lldb::offset_t *offset_ptr,
+                              lldb::offset_t length) const {
     const uint8_t *ptr = PeekData(*offset_ptr, length);
     if (ptr)
       *offset_ptr += length;
@@ -829,7 +830,8 @@ class DataExtractor {
   ///     A non-nullptr data pointer if \a offset is a valid offset and
   ///     there are \a length bytes available at that offset, nullptr
   ///     otherwise.
-  const uint8_t *PeekData(lldb::offset_t offset, lldb::offset_t length) const {
+  virtual const uint8_t *PeekData(lldb::offset_t offset,
+                                  lldb::offset_t length) const {
     if (ValidOffsetForDataOfSize(offset, length))
       return m_start + offset;
     return nullptr;

lldb/include/lldb/Utility/VirtualDataExtractor.h

@@ -0,0 +1,69 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_UTILITY_VIRTUALDATAEXTRACTOR_H
+#define LLDB_UTILITY_VIRTUALDATAEXTRACTOR_H
+
+#include "lldb/Utility/DataExtractor.h"
+#include "lldb/Utility/RangeMap.h"
+#include "lldb/lldb-types.h"
+
+namespace lldb_private {
+
+/// A DataExtractor subclass that allows reading data at virtual addresses
+/// using a lookup table that maps virtual address ranges to physical offsets.
+///
+/// This class maintains a lookup table where each entry contains:
+/// - base: starting virtual address for this entry
+/// - size: size of this entry in bytes
+/// - data: physical offset in the underlying data buffer
+///
+/// Reads are translated from virtual addresses to physical offsets using
+/// this lookup table. Reads cannot cross entry boundaries and this is
+/// enforced with assertions.
+class VirtualDataExtractor : public DataExtractor {
+public:
+  /// Type alias for the range map used internally.
+  /// Maps virtual addresses (base) to physical offsets (data).
+  using LookupTable =
+      RangeDataVector<lldb::offset_t, lldb::offset_t, lldb::offset_t>;
+
+  VirtualDataExtractor() = default;
+
+  VirtualDataExtractor(const void *data, lldb::offset_t data_length,
+                       lldb::ByteOrder byte_order, uint32_t addr_size,
+                       LookupTable lookup_table);
+
+  VirtualDataExtractor(const lldb::DataBufferSP &data_sp,
+                       lldb::ByteOrder byte_order, uint32_t addr_size,
+                       LookupTable lookup_table);
+
+  const void *GetData(lldb::offset_t *offset_ptr,
+                      lldb::offset_t length) const override;
+
+  const uint8_t *PeekData(lldb::offset_t offset,
+                          lldb::offset_t length) const override;
+
+  const LookupTable &GetLookupTable() const { return m_lookup_table; }
+
+protected:
+  /// Find the lookup entry that contains the given virtual address.
+  const LookupTable::Entry *FindEntry(lldb::offset_t virtual_addr) const;
+
+  /// Validate that a read at a virtual address is within bounds and
+  /// does not cross entry boundaries.
+  bool ValidateVirtualRead(lldb::offset_t virtual_addr,
+                           lldb::offset_t length) const;
+
+private:
+  LookupTable m_lookup_table;
+};
+
+} // namespace lldb_private
+
+#endif // LLDB_UTILITY_VIRTUALDATAEXTRACTOR_H

lldb/source/Utility/CMakeLists.txt

@@ -78,6 +78,7 @@ add_lldb_library(lldbUtility NO_INTERNAL_DEPENDENCIES
   UserIDResolver.cpp
   VASprintf.cpp
   VMRange.cpp
+  VirtualDataExtractor.cpp
   XcodeSDK.cpp
   ZipFile.cpp
 

lldb/source/Utility/VirtualDataExtractor.cpp

@@ -0,0 +1,95 @@
+//===----------------------------------------------------------------------===//
+//
+// 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/Utility/VirtualDataExtractor.h"
+#include <cassert>
+
+using namespace lldb;
+using namespace lldb_private;
+
+VirtualDataExtractor::VirtualDataExtractor(const void *data,
+                                           offset_t data_length,
+                                           ByteOrder byte_order,
+                                           uint32_t addr_size,
+                                           LookupTable lookup_table)
+    : DataExtractor(data, data_length, byte_order, addr_size),
+      m_lookup_table(std::move(lookup_table)) {
+  m_lookup_table.Sort();
+}
+
+VirtualDataExtractor::VirtualDataExtractor(const DataBufferSP &data_sp,
+                                           ByteOrder byte_order,
+                                           uint32_t addr_size,
+                                           LookupTable lookup_table)
+    : DataExtractor(data_sp, byte_order, addr_size),
+      m_lookup_table(std::move(lookup_table)) {
+  m_lookup_table.Sort();
+}
+
+const VirtualDataExtractor::LookupTable::Entry *
+VirtualDataExtractor::FindEntry(offset_t virtual_addr) const {
+  // Use RangeDataVector's binary search instead of linear search.
+  return m_lookup_table.FindEntryThatContains(virtual_addr);
+}
+
+bool VirtualDataExtractor::ValidateVirtualRead(offset_t virtual_addr,
+                                               offset_t length) const {
+  const LookupTable::Entry *entry = FindEntry(virtual_addr);
+  if (!entry)
+    return false;
+
+  // Assert that the read does not cross entry boundaries.
+  // RangeData.Contains() checks if a range is fully contained.
+  assert(entry->Contains(LookupTable::Range(virtual_addr, length)) &&
+         "Read crosses lookup table entry boundary");
+
+  // Also validate that the physical offset is within the data buffer.
+  // RangeData.data contains the physical offset.
+  offset_t physical_offset = entry->data + (virtual_addr - entry->base);
+  return ValidOffsetForDataOfSize(physical_offset, length);
+}
+
+const void *VirtualDataExtractor::GetData(offset_t *offset_ptr,
+                                          offset_t length) const {
+  // Override to treat offset as virtual address.
+  if (!offset_ptr)
+    return nullptr;
+
+  offset_t virtual_addr = *offset_ptr;
+
+  if (!ValidateVirtualRead(virtual_addr, length))
+    return nullptr;
+
+  const LookupTable::Entry *entry = FindEntry(virtual_addr);
+  assert(entry && "ValidateVirtualRead should have found an entry");
+
+  offset_t physical_offset = entry->data + (virtual_addr - entry->base);
+  // Use base class PeekData directly to avoid recursion.
+  const void *result = DataExtractor::PeekData(physical_offset, length);
+
+  if (result) {
+    // Advance the virtual offset pointer.
+    *offset_ptr += length;
+  }
+
+  return result;
+}
+
+const uint8_t *VirtualDataExtractor::PeekData(offset_t offset,
+                                              offset_t length) const {
+  // Override to treat offset as virtual address.
+  if (!ValidateVirtualRead(offset, length))
+    return nullptr;
+
+  const LookupTable::Entry *entry = FindEntry(offset);
+  assert(entry && "ValidateVirtualRead should have found an entry");
+
+  offset_t physical_offset = entry->data + (offset - entry->base);
+  // Use the base class PeekData with the physical offset.
+  return DataExtractor::PeekData(physical_offset, length);
+}

lldb/unittests/Utility/CMakeLists.txt

@@ -48,6 +48,7 @@ add_lldb_unittest(UtilityTests
   UserIDResolverTest.cpp
   UUIDTest.cpp
   VASprintfTest.cpp
+  VirtualDataExtractorTest.cpp
   VMRangeTest.cpp
   XcodeSDKTest.cpp