DYLDRendezvous.h

//===-- DYLDRendezvous.h ----------------------------------------*- 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 LLDB_SOURCE_PLUGINS_DYNAMICLOADER_POSIX_DYLD_DYLDRENDEZVOUS_H
#define LLDB_SOURCE_PLUGINS_DYNAMICLOADER_POSIX_DYLD_DYLDRENDEZVOUS_H

#include <list>
#include <string>

#include "lldb/Utility/FileSpec.h"
#include "lldb/lldb-defines.h"
#include "lldb/lldb-types.h"

#include "lldb/Core/LoadedModuleInfoList.h"

using lldb_private::LoadedModuleInfoList;

namespace lldb_private {
class Log;
class Process;
}

/// \class DYLDRendezvous
/// Interface to the runtime linker.
///
/// A structure is present in a processes memory space which is updated by the
/// dynamic linker each time a module is loaded or unloaded.  This class
/// provides an interface to this structure and maintains a consistent
/// snapshot of the currently loaded modules.
///
/// In the dynamic loader sources, this structure has a type of "r_debug" and
/// the name of the structure us "_r_debug". The structure looks like:
///
/// struct r_debug {
///     // Version number for this protocol.
///     int r_version;
///     // Head of the chain of loaded objects.
///     struct link_map *r_map;
///     // The address the debugger should set a breakpoint at in order to get
///     // notified when shared libraries are added or removed
///     uintptr_t r_brk;
///     // This state value describes the mapping change taking place when the
///     // 'r_brk' address is called.
///     enum {
///       RT_CONSISTENT, // Mapping change is complete.
///       RT_ADD,        // Beginning to add a new object.
///       RT_DELETE,     // Beginning to remove an object mapping.
///     } r_state;
///     // Base address the linker is loaded at.
///     uintptr_t r_ldbase;
///   };
///
/// The dynamic linker then defines a global variable using this type named
/// "_r_debug":
///
///   r_debug _r_debug;
///
/// The DYLDRendezvous class defines a local version of this structure named
/// DYLDRendezvous::Rendezvous. See the definition inside the class definition
/// for DYLDRendezvous.
///
/// This structure can be located by looking through the .dynamic section in
/// the main executable and finding the DT_DEBUG tag entry. This value starts
/// out with a value of zero when the program first is initially loaded, but
/// the address of the "_r_debug" structure from ld.so is filled in by the
/// dynamic loader during program initialization code in ld.so prior to loading
/// or unloading and shared libraries.
///
/// The dynamic loader will update this structure as shared libraries are
/// loaded and will call a specific function that LLDB knows to set a
/// breakpoint on (from _r_debug.r_brk) so LLDB will find out when shared
/// libraries are loaded or unloaded. Each time this breakpoint is hit, LLDB
/// looks at the contents of this structure and the contents tell LLDB what
/// needs to be done.
///
/// Currently we expect the "state" in this structure to change as things
/// happen.
///
/// When any shared libraries are loaded the following happens:
/// - _r_debug.r_map is updated with the new shared libraries. This is a
///   doubly linked list of "link_map *" entries.
/// - _r_debug.r_state is set to RT_ADD and the debugger notification
///   function is called notifying the debugger that shared libraries are
///   about to be added, but are not yet ready for use.
/// - Once the the shared libraries are fully loaded, _r_debug.r_state is set
///   to RT_CONSISTENT and the debugger notification function is called again
///   notifying the debugger that shared libraries are ready for use.
///   DYLDRendezvous must remember that the previous state was RT_ADD when it
///   receives a RT_CONSISTENT in order to know to add libraries
///
/// When any shared libraries are unloaded the following happens:
/// - _r_debug.r_map is updated and the unloaded libraries are removed.
/// - _r_debug.r_state is set to RT_DELETE and the debugger notification
///   function is called notifying the debugger that shared libraries are
///   about to be removed.
/// - Once the the shared libraries are removed _r_debug.r_state is set to
///   RT_CONSISTENT and the debugger notification function is called again
///   notifying the debugger that shared libraries have been removed.
///   DYLDRendezvous must remember that the previous state was RT_DELETE when
///   it receives a RT_CONSISTENT in order to know to remove libraries
///
class DYLDRendezvous {

  // This structure is used to hold the contents of the debug rendezvous
  // information (struct r_debug) as found in the inferiors memory.  Note that
  // the layout of this struct is not binary compatible, it is simply large
  // enough to hold the information on both 32 and 64 bit platforms.
  struct Rendezvous {
    uint64_t version = 0;
    lldb::addr_t map_addr = 0;
    lldb::addr_t brk = 0;
    uint64_t state = 0;
    lldb::addr_t ldbase = 0;

    Rendezvous() = default;

    void DumpToLog(lldb_private::Log *log, const char *label);
  };

  /// Locates the address of the rendezvous structure.  It updates
  /// m_executable_interpreter if address is extracted from _r_debug.
  ///
  /// \returns address on success and LLDB_INVALID_ADDRESS on failure.
  lldb::addr_t ResolveRendezvousAddress();

public:
  // Various metadata supplied by the inferior's threading library to describe
  // the per-thread state.
  struct ThreadInfo {
    bool valid;             // whether we read valid metadata
    uint32_t dtv_offset;    // offset of DTV pointer within pthread
    uint32_t dtv_slot_size; // size of one DTV slot
    uint32_t modid_offset;  // offset of module ID within link_map
    uint32_t tls_offset;    // offset of TLS pointer within DTV slot
  };

  DYLDRendezvous(lldb_private::Process *process);

  /// Update the cached executable path.
  void UpdateExecutablePath();

  /// Update the internal snapshot of runtime linker rendezvous and recompute
  /// the currently loaded modules.
  ///
  /// This method should be called once one start up, then once each time the
  /// runtime linker enters the function given by GetBreakAddress().
  ///
  /// \returns true on success and false on failure.
  ///
  /// \see GetBreakAddress().
  bool Resolve();

  /// \returns true if this rendezvous has been located in the inferiors
  /// address space and false otherwise.
  bool IsValid();

  /// \returns the address of the rendezvous structure in the inferiors
  /// address space.
  lldb::addr_t GetRendezvousAddress() const { return m_rendezvous_addr; }

  /// \returns the version of the rendezvous protocol being used.
  uint64_t GetVersion() const { return m_current.version; }

  /// \returns address in the inferiors address space containing the linked
  /// list of shared object descriptors.
  lldb::addr_t GetLinkMapAddress() const { return m_current.map_addr; }

  /// A breakpoint should be set at this address and Resolve called on each
  /// hit.
  ///
  /// \returns the address of a function called by the runtime linker each
  /// time a module is loaded/unloaded, or about to be loaded/unloaded.
  ///
  /// \see Resolve()
  lldb::addr_t GetBreakAddress() const { return m_current.brk; }

  /// Returns the current state of the rendezvous structure.
  uint64_t GetState() const { return m_current.state; }

  /// \returns the base address of the runtime linker in the inferiors address
  /// space.
  lldb::addr_t GetLDBase() const { return m_current.ldbase; }

  /// \returns the thread layout metadata from the inferiors thread library.
  const ThreadInfo &GetThreadInfo();

  /// \returns true if modules have been loaded into the inferior since the
  /// last call to Resolve().
  bool ModulesDidLoad() const { return !m_added_soentries.empty(); }

  /// \returns true if modules have been unloaded from the inferior since the
  /// last call to Resolve().
  bool ModulesDidUnload() const { return !m_removed_soentries.empty(); }

  void DumpToLog(lldb_private::Log *log) const;

  /// Constants describing the state of the rendezvous.
  ///
  /// These values are defined to match the r_debug.r_state enum from the
  /// actual dynamic loader sources.
  ///
  /// \see GetState().
  enum RendezvousState {
    eConsistent, // RT_CONSISTENT
    eAdd,        // RT_ADD
    eDelete      // RT_DELETE
  };

  /// Structure representing the shared objects currently loaded into the
  /// inferior process.
  ///
  /// This object is a rough analogue to the struct link_map object which
  /// actually lives in the inferiors memory.
  struct SOEntry {
    lldb::addr_t link_addr;           ///< Address of this link_map.
    lldb::addr_t base_addr;           ///< Base address of the loaded object.
    lldb::addr_t path_addr;           ///< String naming the shared object.
    lldb::addr_t dyn_addr;            ///< Dynamic section of shared object.
    lldb::addr_t next;                ///< Address of next so_entry.
    lldb::addr_t prev;                ///< Address of previous so_entry.
    lldb_private::FileSpec file_spec; ///< File spec of shared object.

    SOEntry() { clear(); }

    bool operator==(const SOEntry &entry) {
      return file_spec == entry.file_spec;
    }

    void clear() {
      link_addr = 0;
      base_addr = 0;
      path_addr = 0;
      dyn_addr = 0;
      next = 0;
      prev = 0;
      file_spec.Clear();
    }
  };

protected:
  typedef std::list<SOEntry> SOEntryList;

public:
  typedef SOEntryList::const_iterator iterator;

  /// Iterators over all currently loaded modules.
  iterator begin() const { return m_soentries.begin(); }
  iterator end() const { return m_soentries.end(); }

  /// Iterators over all modules loaded into the inferior since the last call
  /// to Resolve().
  iterator loaded_begin() const { return m_added_soentries.begin(); }
  iterator loaded_end() const { return m_added_soentries.end(); }

  /// Iterators over all modules unloaded from the inferior since the last
  /// call to Resolve().
  iterator unloaded_begin() const { return m_removed_soentries.begin(); }
  iterator unloaded_end() const { return m_removed_soentries.end(); }

protected:
  lldb_private::Process *m_process;

  // Cached copy of executable file spec
  lldb_private::FileSpec m_exe_file_spec;

  /// Location of the r_debug structure in the inferiors address space.
  lldb::addr_t m_rendezvous_addr;

  // True if the main program is the dynamic linker/loader/program interpreter.
  bool m_executable_interpreter;

  /// Current and previous snapshots of the rendezvous structure.
  Rendezvous m_current;
  Rendezvous m_previous;

  /// List of currently loaded SO modules
  LoadedModuleInfoList m_loaded_modules;

  /// List of SOEntry objects corresponding to the current link map state.
  SOEntryList m_soentries;

  /// List of SOEntry's added to the link map since the last call to
  /// Resolve().
  SOEntryList m_added_soentries;

  /// List of SOEntry's removed from the link map since the last call to
  /// Resolve().
  SOEntryList m_removed_soentries;

  /// Threading metadata read from the inferior.
  ThreadInfo m_thread_info;

  /// Reads an unsigned integer of \p size bytes from the inferior's address
  /// space starting at \p addr.
  ///
  /// \returns addr + size if the read was successful and false otherwise.
  lldb::addr_t ReadWord(lldb::addr_t addr, uint64_t *dst, size_t size);

  /// Reads an address from the inferior's address space starting at \p addr.
  ///
  /// \returns addr + target address size if the read was successful and
  /// 0 otherwise.
  lldb::addr_t ReadPointer(lldb::addr_t addr, lldb::addr_t *dst);

  /// Reads a null-terminated C string from the memory location starting at @p
  /// addr.
  std::string ReadStringFromMemory(lldb::addr_t addr);

  /// Reads an SOEntry starting at \p addr.
  bool ReadSOEntryFromMemory(lldb::addr_t addr, SOEntry &entry);

  /// Updates the current set of SOEntries, the set of added entries, and the
  /// set of removed entries.
  bool UpdateSOEntries();

  /// Same as UpdateSOEntries but it gets the list of loaded modules from the
  /// remote debug server (faster when supported).
  bool UpdateSOEntriesFromRemote();

  bool FillSOEntryFromModuleInfo(
      LoadedModuleInfoList::LoadedModuleInfo const &modInfo, SOEntry &entry);

  bool SaveSOEntriesFromRemote(const LoadedModuleInfoList &module_list);

  bool AddSOEntriesFromRemote(const LoadedModuleInfoList &module_list);

  bool RemoveSOEntriesFromRemote(const LoadedModuleInfoList &module_list);

  bool AddSOEntries();

  bool RemoveSOEntries();

  void UpdateBaseAddrIfNecessary(SOEntry &entry, std::string const &file_path);

  void UpdateFileSpecIfNecessary(SOEntry &entry);

  bool SOEntryIsMainExecutable(const SOEntry &entry);

  /// Reads the current list of shared objects according to the link map
  /// supplied by the runtime linker.
  bool TakeSnapshot(SOEntryList &entry_list);

  enum PThreadField { eSize, eNElem, eOffset };

  bool FindMetadata(const char *name, PThreadField field, uint32_t &value);

  bool IsCoreFile() const;

  enum RendezvousAction {
    eNoAction,
    eTakeSnapshot,
    eAddModules,
    eRemoveModules
  };

  static const char *StateToCStr(RendezvousState state);
  static const char *ActionToCStr(RendezvousAction action);

  /// Returns the current action to be taken given the current and previous
  /// state
  RendezvousAction GetAction() const;
};

#endif