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 //===-- TraceDumper.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
 //
 //===----------------------------------------------------------------------===//
 
 #include "lldb/Symbol/SymbolContext.h"
 #include "lldb/Target/TraceCursor.h"
 #include <optional>
 #include <stack>
 
 #ifndef LLDB_TARGET_TRACE_INSTRUCTION_DUMPER_H
 #define LLDB_TARGET_TRACE_INSTRUCTION_DUMPER_H
 
 namespace lldb_private {
 
 /// Class that holds the configuration used by \a TraceDumper for
 /// traversing and dumping instructions.
 struct TraceDumperOptions {
   /// If \b true, the cursor will be iterated forwards starting from the
   /// oldest instruction. Otherwise, the iteration starts from the most
   /// recent instruction.
   bool forwards = false;
   /// Dump only instruction addresses without disassembly nor symbol
   /// information.
   bool raw = false;
   /// Dump in json format.
   bool json = false;
   /// When dumping in JSON format, pretty print the output.
   bool pretty_print_json = false;
   /// For each trace item, print the corresponding timestamp in nanoseconds if
   /// available.
   bool show_timestamps = false;
   /// Dump the events that happened between instructions.
   bool show_events = false;
   /// Dump events and none of the instructions.
   bool only_events = false;
   /// For each instruction, print the instruction kind.
   bool show_control_flow_kind = false;
   /// Optional custom id to start traversing from.
   std::optional<uint64_t> id;
   /// Optional number of instructions to skip from the starting position
   /// of the cursor.
   std::optional<size_t> skip;
 };
 
 /// Class used to dump the instructions of a \a TraceCursor using its current
 /// state and granularity.
 class TraceDumper {
 public:
   /// Helper struct that holds symbol, disassembly and address information of an
   /// instruction.
   struct SymbolInfo {
     SymbolContext sc;
     Address address;
     lldb::DisassemblerSP disassembler;
     lldb::InstructionSP instruction;
     lldb_private::ExecutionContext exe_ctx;
   };
 
   /// Helper struct that holds all the information we know about a trace item
   struct TraceItem {
     lldb::user_id_t id;
     lldb::addr_t load_address;
     std::optional<double> timestamp;
     std::optional<uint64_t> hw_clock;
     std::optional<std::string> sync_point_metadata;
     std::optional<llvm::StringRef> error;
     std::optional<lldb::TraceEvent> event;
     std::optional<SymbolInfo> symbol_info;
     std::optional<SymbolInfo> prev_symbol_info;
     std::optional<lldb::cpu_id_t> cpu_id;
   };
 
   /// An object representing a traced function call.
   ///
   /// A function call is represented using segments and subcalls.
   ///
   /// TracedSegment:
   ///   A traced segment is a maximal list of consecutive traced instructions
   ///   that belong to the same function call. A traced segment will end in
   ///   three possible ways:
   ///     - With a call to a function deeper in the callstack. In this case,
   ///     most of the times this nested call will return
   ///       and resume with the next segment of this segment's owning function
   ///       call. More on this later.
   ///     - Abruptly due to end of trace. In this case, we weren't able to trace
   ///     the end of this function call.
   ///     - Simply a return higher in the callstack.
   ///
   ///   In terms of implementation details, as segment can be represented with
   ///   the beginning and ending instruction IDs from the instruction trace.
   ///
   ///  UntracedPrefixSegment:
   ///   It might happen that we didn't trace the beginning of a function and we
   ///   saw it for the first time as part of a return. As a way to signal these
   ///   cases, we have a placeholder UntracedPrefixSegment class that completes the
   ///   callgraph.
   ///
   ///  Example:
   ///   We might have this piece of execution:
   ///
   ///     main() [offset 0x00 to 0x20] [traced instruction ids 1 to 4]
   ///       foo()  [offset 0x00 to 0x80] [traced instruction ids 5 to 20] # main
   ///       invoked foo
   ///     main() [offset 0x24 to 0x40] [traced instruction ids 21 to 30]
   ///
   ///   In this case, our function main invokes foo. We have 3 segments: main
   ///   [offset 0x00 to 0x20], foo() [offset 0x00 to 0x80], and main() [offset
   ///   0x24 to 0x40]. We also have the instruction ids from the corresponding
   ///   linear instruction trace for each segment.
   ///
   ///   But what if we started tracing since the middle of foo? Then we'd have
   ///   an incomplete trace
   ///
   ///       foo() [offset 0x30 to 0x80] [traced instruction ids 1 to 10]
   ///     main() [offset 0x24 to 0x40] [traced instruction ids 11 to 20]
   ///
   ///   Notice that we changed the instruction ids because this is a new trace.
   ///   Here, in order to have a somewhat complete tree with good traversal
   ///   capabilities, we can create an UntracedPrefixSegment to signal the portion of
   ///   main() that we didn't trace. We don't know if this segment was in fact
   ///   multiple segments with many function calls. We'll never know. The
   ///   resulting tree looks like the following:
   ///
   ///     main() [untraced]
   ///       foo() [offset 0x30 to 0x80] [traced instruction ids 1 to 10]
   ///     main() [offset 0x24 to 0x40] [traced instruction ids 11 to 20]
   ///
   ///   And in pseudo-code:
   ///
   ///     FunctionCall [
   ///       UntracedPrefixSegment {
   ///         symbol: main()
   ///         nestedCall: FunctionCall [ # this untraced segment has a nested
   ///         call
   ///           TracedSegment {
   ///             symbol: foo()
   ///             fromInstructionId: 1
   ///             toInstructionId: 10
   ///             nestedCall: none # this doesn't have a nested call
   ///           }
   ///         }
   ///       ],
   ///       TracedSegment {
   ///         symbol: main()
   ///         fromInstructionId: 11
   ///         toInstructionId: 20
   ///         nestedCall: none # this also doesn't have a nested call
   ///       }
   ///   ]
   ///
   ///   We can see the nested structure and how instructions are represented as
   ///   segments.
   ///
   ///
   ///   Returns:
   ///     Code doesn't always behave intuitively. Some interesting functions
   ///     might modify the stack and thus change the behavior of common
   ///     instructions like CALL and RET. We try to identify these cases, and
   ///     the result is that the return edge from a segment might connect with a
   ///     function call very high the stack. For example, you might have
   ///
   ///     main()
   ///       foo()
   ///         bar()
   ///         # here bar modifies the stack and pops foo() from it. Then it
   ///         finished the a RET (return)
   ///     main() # we came back directly to main()
   ///
   ///     I have observed some trampolines doing this, as well as some std
   ///     functions (like ostream functions). So consumers should be aware of
   ///     this.
   ///
   ///     There are all sorts of "abnormal" behaviors you can see in code, and
   ///     whenever we fail at identifying what's going on, we prefer to create a
   ///     new tree.
   ///
   ///   Function call forest:
   ///     A single tree would suffice if a trace didn't contain errors nor
   ///     abnormal behaviors that made our algorithms fail. Sadly these
   ///     anomalies exist and we prefer not to use too many heuristics and
   ///     probably end up lying to the user. So we create a new tree from the
   ///     point we can't continue using the previous tree. This results in
   ///     having a forest instead of a single tree. This is probably the best we
   ///     can do if we consumers want to use this data to perform performance
   ///     analysis or reverse debugging.
   ///
   ///   Non-functions:
   ///     Not everything in a program is a function. There are blocks of
   ///     instructions that are simply labeled or even regions without symbol
   ///     information that we don't what they are. We treat all of them as
   ///     functions for simplicity.
   ///
   ///   Errors:
   ///     Whenever an error is found, a new tree with a single segment is
   ///     created. All consecutive errors after the original one are then
   ///     appended to this segment. As a note, something that GDB does is to use
   ///     some heuristics to merge trees that were interrupted by errors. We are
   ///     leaving that out of scope until a feature like that one is really
   ///     needed.
 
   /// Forward declaration
   class FunctionCall;
   using FunctionCallUP = std::unique_ptr<FunctionCall>;
 
   class FunctionCall {
   public:
     class TracedSegment {
     public:
       /// \param[in] cursor_sp
       ///   A cursor pointing to the beginning of the segment.
       ///
       /// \param[in] symbol_info
       ///   The symbol information of the first instruction of the segment.
       ///
       /// \param[in] call
       ///   The FunctionCall object that owns this segment.
       TracedSegment(const lldb::TraceCursorSP &cursor_sp,
                     const SymbolInfo &symbol_info, FunctionCall &owning_call)
           : m_first_insn_id(cursor_sp->GetId()),
             m_last_insn_id(cursor_sp->GetId()),
             m_first_symbol_info(symbol_info), m_last_symbol_info(symbol_info),
             m_owning_call(owning_call) {}
 
       /// \return
       ///   The chronologically first instruction ID in this segment.
       lldb::user_id_t GetFirstInstructionID() const;
       /// \return
       ///   The chronologically last instruction ID in this segment.
       lldb::user_id_t GetLastInstructionID() const;
 
       /// \return
       ///   The symbol information of the chronologically first instruction ID
       ///   in this segment.
       const SymbolInfo &GetFirstInstructionSymbolInfo() const;
 
       /// \return
       ///   The symbol information of the chronologically last instruction ID in
       ///   this segment.
       const SymbolInfo &GetLastInstructionSymbolInfo() const;
 
       /// \return
       ///   Get the call that owns this segment.
       const FunctionCall &GetOwningCall() const;
 
       /// Append a new instruction to this segment.
       ///
       /// \param[in] cursor_sp
       ///   A cursor pointing to the new instruction.
       ///
       /// \param[in] symbol_info
       ///   The symbol information of the new instruction.
       void AppendInsn(const lldb::TraceCursorSP &cursor_sp,
                       const SymbolInfo &symbol_info);
 
       /// Create a nested call at the end of this segment.
       ///
       /// \param[in] cursor_sp
       ///   A cursor pointing to the first instruction of the nested call.
       ///
       /// \param[in] symbol_info
       ///   The symbol information of the first instruction of the nested call.
       FunctionCall &CreateNestedCall(const lldb::TraceCursorSP &cursor_sp,
                                      const SymbolInfo &symbol_info);
 
       /// Executed the given callback if there's a nested call at the end of
       /// this segment.
       void IfNestedCall(std::function<void(const FunctionCall &function_call)>
                             callback) const;
 
     private:
       TracedSegment(const TracedSegment &) = delete;
       TracedSegment &operator=(TracedSegment const &);
 
       /// Delimiting instruction IDs taken chronologically.
       /// \{
       lldb::user_id_t m_first_insn_id;
       lldb::user_id_t m_last_insn_id;
       /// \}
       /// An optional nested call starting at the end of this segment.
       FunctionCallUP m_nested_call;
       /// The symbol information of the delimiting instructions
       /// \{
       SymbolInfo m_first_symbol_info;
       SymbolInfo m_last_symbol_info;
       /// \}
       FunctionCall &m_owning_call;
     };
 
     class UntracedPrefixSegment {
     public:
       /// Note: Untraced segments can only exist if have also seen a traced
       /// segment of the same function call. Thus, we can use those traced
       /// segments if we want symbol information and such.
 
       UntracedPrefixSegment(FunctionCallUP &&nested_call)
           : m_nested_call(std::move(nested_call)) {}
 
       const FunctionCall &GetNestedCall() const;
 
     private:
       UntracedPrefixSegment(const UntracedPrefixSegment &) = delete;
       UntracedPrefixSegment &operator=(UntracedPrefixSegment const &);
       FunctionCallUP m_nested_call;
     };
 
     /// Create a new function call given an instruction. This will also create a
     /// segment for that instruction.
     ///
     /// \param[in] cursor_sp
     ///   A cursor pointing to the first instruction of that function call.
     ///
     /// \param[in] symbol_info
     ///   The symbol information of that first instruction.
     FunctionCall(const lldb::TraceCursorSP &cursor_sp,
                  const SymbolInfo &symbol_info);
 
     /// Append a new traced segment to this function call.
     ///
     /// \param[in] cursor_sp
     ///   A cursor pointing to the first instruction of the new segment.
     ///
     /// \param[in] symbol_info
     ///   The symbol information of that first instruction.
     void AppendSegment(const lldb::TraceCursorSP &cursor_sp,
                        const SymbolInfo &symbol_info);
 
     /// \return
     ///   The symbol info of some traced instruction of this call.
     const SymbolInfo &GetSymbolInfo() const;
 
     /// \return
     ///   \b true if and only if the instructions in this function call are
     ///   trace errors, in which case this function call is a fake one.
     bool IsError() const;
 
     /// \return
     ///   The list of traced segments of this call.
     const std::deque<TracedSegment> &GetTracedSegments() const;
 
     /// \return
     ///   A non-const reference to the most-recent traced segment.
     TracedSegment &GetLastTracedSegment();
 
     /// Create an untraced segment for this call that jumps to the provided
     /// nested call.
     void SetUntracedPrefixSegment(FunctionCallUP &&nested_call);
 
     /// \return
     ///   A optional to the untraced prefix segment of this call.
     const std::optional<UntracedPrefixSegment> &
     GetUntracedPrefixSegment() const;
 
     /// \return
     ///   A pointer to the parent call. It may be \b nullptr.
     FunctionCall *GetParentCall() const;
 
     void SetParentCall(FunctionCall &parent_call);
 
   private:
     /// An optional untraced segment that precedes all the traced segments.
     std::optional<UntracedPrefixSegment> m_untraced_prefix_segment;
     /// The traced segments in order. We used a deque to prevent moving these
     /// objects when appending to the list, which would happen with vector.
     std::deque<TracedSegment> m_traced_segments;
     /// The parent call, which might be null. Useful for reconstructing
     /// callstacks.
     FunctionCall *m_parent_call = nullptr;
     /// Whether this call represents a list of consecutive errors.
     bool m_is_error;
   };
 
   /// Interface used to abstract away the format in which the instruction
   /// information will be dumped.
   class OutputWriter {
   public:
     virtual ~OutputWriter() = default;
 
     /// Notify this writer that the cursor ran out of data.
     virtual void NoMoreData() {}
 
     /// Dump a trace item (instruction, error or event).
     virtual void TraceItem(const TraceItem &item) = 0;
 
     /// Dump a function call forest.
     virtual void
     FunctionCallForest(const std::vector<FunctionCallUP> &forest) = 0;
   };
 
   /// Create a instruction dumper for the cursor.
   ///
   /// \param[in] cursor
   ///     The cursor whose instructions will be dumped.
   ///
   /// \param[in] s
   ///     The stream where to dump the instructions to.
   ///
   /// \param[in] options
   ///     Additional options for configuring the dumping.
   TraceDumper(lldb::TraceCursorSP cursor_sp, Stream &s,
               const TraceDumperOptions &options);
 
   /// Dump \a count instructions of the thread trace starting at the current
   /// cursor position.
   ///
   /// This effectively moves the cursor to the next unvisited position, so that
   /// a subsequent call to this method continues where it left off.
   ///
   /// \param[in] count
   ///     The number of instructions to print.
   ///
   /// \return
   ///     The instruction id of the last traversed instruction, or \b
   ///     std::nullopt if no instructions were visited.
   std::optional<lldb::user_id_t> DumpInstructions(size_t count);
 
   /// Dump all function calls forwards chronologically and hierarchically
   void DumpFunctionCalls();
 
 private:
   /// Create a trace item for the current position without symbol information.
   TraceItem CreatRawTraceItem();
 
   lldb::TraceCursorSP m_cursor_sp;
   TraceDumperOptions m_options;
   std::unique_ptr<OutputWriter> m_writer_up;
 };
 
 } // namespace lldb_private
 
 #endif // LLDB_TARGET_TRACE_INSTRUCTION_DUMPER_H

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