xray_fdr_controller.h

//===-- xray_fdr_controller.h ---------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file is a part of XRay, a function call tracing system.
//
//===----------------------------------------------------------------------===//
#ifndef COMPILER_RT_LIB_XRAY_XRAY_FDR_CONTROLLER_H_
#define COMPILER_RT_LIB_XRAY_XRAY_FDR_CONTROLLER_H_

#include <limits>
#include <time.h>

#include "xray/xray_interface.h"
#include "xray/xray_records.h"
#include "xray_buffer_queue.h"
#include "xray_fdr_log_writer.h"

namespace __xray {

template <size_t Version = 5> class FDRController {
  BufferQueue *BQ;
  BufferQueue::Buffer &B;
  FDRLogWriter &W;
  int (*WallClockReader)(clockid_t, struct timespec *) = 0;
  uint64_t CycleThreshold = 0;

  uint64_t LastFunctionEntryTSC = 0;
  uint64_t LatestTSC = 0;
  uint16_t LatestCPU = 0;
  tid_t TId = 0;
  pid_t PId = 0;
  bool First = true;

  uint32_t UndoableFunctionEnters = 0;
  uint32_t UndoableTailExits = 0;

  bool finalized() const XRAY_NEVER_INSTRUMENT {
    return BQ == nullptr || BQ->finalizing();
  }

  bool hasSpace(size_t S) XRAY_NEVER_INSTRUMENT {
    return B.Data != nullptr && B.Generation == BQ->generation() &&
           W.getNextRecord() + S <= reinterpret_cast<char *>(B.Data) + B.Size;
  }

  constexpr int32_t mask(int32_t FuncId) const XRAY_NEVER_INSTRUMENT {
    return FuncId & ((1 << 29) - 1);
  }

  bool getNewBuffer() XRAY_NEVER_INSTRUMENT {
    if (BQ->getBuffer(B) != BufferQueue::ErrorCode::Ok)
      return false;

    W.resetRecord();
    DCHECK_EQ(W.getNextRecord(), B.Data);
    LatestTSC = 0;
    LatestCPU = 0;
    First = true;
    UndoableFunctionEnters = 0;
    UndoableTailExits = 0;
    atomic_store(B.Extents, 0, memory_order_release);
    return true;
  }

  bool setupNewBuffer() XRAY_NEVER_INSTRUMENT {
    if (finalized())
      return false;

    DCHECK(hasSpace(sizeof(MetadataRecord) * 3));
    TId = GetTid();
    PId = internal_getpid();
    struct timespec TS {
      0, 0
    };
    WallClockReader(CLOCK_MONOTONIC, &TS);

    MetadataRecord Metadata[] = {
        // Write out a MetadataRecord to signify that this is the start of a new
        // buffer, associated with a particular thread, with a new CPU. For the
        // data, we have 15 bytes to squeeze as much information as we can. At
        // this point we only write down the following bytes:
        //   - Thread ID (tid_t, cast to 4 bytes type due to Darwin being 8
        //   bytes)
        createMetadataRecord<MetadataRecord::RecordKinds::NewBuffer>(
            static_cast<int32_t>(TId)),

        // Also write the WalltimeMarker record. We only really need microsecond
        // precision here, and enforce across platforms that we need 64-bit
        // seconds and 32-bit microseconds encoded in the Metadata record.
        createMetadataRecord<MetadataRecord::RecordKinds::WalltimeMarker>(
            static_cast<int64_t>(TS.tv_sec),
            static_cast<int32_t>(TS.tv_nsec / 1000)),

        // Also write the Pid record.
        createMetadataRecord<MetadataRecord::RecordKinds::Pid>(
            static_cast<int32_t>(PId)),
    };

    if (finalized())
      return false;
    return W.writeMetadataRecords(Metadata);
  }

  bool prepareBuffer(size_t S) XRAY_NEVER_INSTRUMENT {
    if (finalized())
      return returnBuffer();

    if (UNLIKELY(!hasSpace(S))) {
      if (!returnBuffer())
        return false;
      if (!getNewBuffer())
        return false;
      if (!setupNewBuffer())
        return false;
    }

    if (First) {
      First = false;
      W.resetRecord();
      atomic_store(B.Extents, 0, memory_order_release);
      return setupNewBuffer();
    }

    return true;
  }

  bool returnBuffer() XRAY_NEVER_INSTRUMENT {
    if (BQ == nullptr)
      return false;

    First = true;
    if (finalized()) {
      BQ->releaseBuffer(B); // ignore result.
      return false;
    }

    return BQ->releaseBuffer(B) == BufferQueue::ErrorCode::Ok;
  }

  enum class PreambleResult { NoChange, WroteMetadata, InvalidBuffer };
  PreambleResult recordPreamble(uint64_t TSC,
                                uint16_t CPU) XRAY_NEVER_INSTRUMENT {
    if (UNLIKELY(LatestCPU != CPU || LatestTSC == 0)) {
      // We update our internal tracking state for the Latest TSC and CPU we've
      // seen, then write out the appropriate metadata and function records.
      LatestTSC = TSC;
      LatestCPU = CPU;

      if (B.Generation != BQ->generation())
        return PreambleResult::InvalidBuffer;

      W.writeMetadata<MetadataRecord::RecordKinds::NewCPUId>(CPU, TSC);
      return PreambleResult::WroteMetadata;
    }

    DCHECK_EQ(LatestCPU, CPU);

    if (UNLIKELY(LatestTSC > TSC ||
                 TSC - LatestTSC >
                     uint64_t{std::numeric_limits<int32_t>::max()})) {
      // Either the TSC has wrapped around from the last TSC we've seen or the
      // delta is too large to fit in a 32-bit signed integer, so we write a
      // wrap-around record.
      LatestTSC = TSC;

      if (B.Generation != BQ->generation())
        return PreambleResult::InvalidBuffer;

      W.writeMetadata<MetadataRecord::RecordKinds::TSCWrap>(TSC);
      return PreambleResult::WroteMetadata;
    }

    return PreambleResult::NoChange;
  }

  bool rewindRecords(int32_t FuncId, uint64_t TSC,
                     uint16_t CPU) XRAY_NEVER_INSTRUMENT {
    // Undo one enter record, because at this point we are either at the state
    // of:
    // - We are exiting a function that we recently entered.
    // - We are exiting a function that was the result of a sequence of tail
    //   exits, and we can check whether the tail exits can be re-wound.
    //
    FunctionRecord F;
    W.undoWrites(sizeof(FunctionRecord));
    if (B.Generation != BQ->generation())
      return false;
    internal_memcpy(&F, W.getNextRecord(), sizeof(FunctionRecord));

    DCHECK(F.RecordKind ==
               uint8_t(FunctionRecord::RecordKinds::FunctionEnter) &&
           "Expected to find function entry recording when rewinding.");
    DCHECK_EQ(F.FuncId, FuncId & ~(0x0F << 28));

    LatestTSC -= F.TSCDelta;
    if (--UndoableFunctionEnters != 0) {
      LastFunctionEntryTSC -= F.TSCDelta;
      return true;
    }

    LastFunctionEntryTSC = 0;
    auto RewindingTSC = LatestTSC;
    auto RewindingRecordPtr = W.getNextRecord() - sizeof(FunctionRecord);
    while (UndoableTailExits) {
      if (B.Generation != BQ->generation())
        return false;
      internal_memcpy(&F, RewindingRecordPtr, sizeof(FunctionRecord));
      DCHECK_EQ(F.RecordKind,
                uint8_t(FunctionRecord::RecordKinds::FunctionTailExit));
      RewindingTSC -= F.TSCDelta;
      RewindingRecordPtr -= sizeof(FunctionRecord);
      if (B.Generation != BQ->generation())
        return false;
      internal_memcpy(&F, RewindingRecordPtr, sizeof(FunctionRecord));

      // This tail call exceeded the threshold duration. It will not be erased.
      if ((TSC - RewindingTSC) >= CycleThreshold) {
        UndoableTailExits = 0;
        return true;
      }

      --UndoableTailExits;
      W.undoWrites(sizeof(FunctionRecord) * 2);
      LatestTSC = RewindingTSC;
    }
    return true;
  }

public:
  template <class WallClockFunc>
  FDRController(BufferQueue *BQ, BufferQueue::Buffer &B, FDRLogWriter &W,
                WallClockFunc R, uint64_t C) XRAY_NEVER_INSTRUMENT
      : BQ(BQ),
        B(B),
        W(W),
        WallClockReader(R),
        CycleThreshold(C) {}

  bool functionEnter(int32_t FuncId, uint64_t TSC,
                     uint16_t CPU) XRAY_NEVER_INSTRUMENT {
    if (finalized() ||
        !prepareBuffer(sizeof(MetadataRecord) + sizeof(FunctionRecord)))
      return returnBuffer();

    auto PreambleStatus = recordPreamble(TSC, CPU);
    if (PreambleStatus == PreambleResult::InvalidBuffer)
      return returnBuffer();

    if (PreambleStatus == PreambleResult::WroteMetadata) {
      UndoableFunctionEnters = 1;
      UndoableTailExits = 0;
    } else {
      ++UndoableFunctionEnters;
    }

    auto Delta = TSC - LatestTSC;
    LastFunctionEntryTSC = TSC;
    LatestTSC = TSC;
    return W.writeFunction(FDRLogWriter::FunctionRecordKind::Enter,
                           mask(FuncId), Delta);
  }

  bool functionTailExit(int32_t FuncId, uint64_t TSC,
                        uint16_t CPU) XRAY_NEVER_INSTRUMENT {
    if (finalized())
      return returnBuffer();

    if (!prepareBuffer(sizeof(MetadataRecord) + sizeof(FunctionRecord)))
      return returnBuffer();

    auto PreambleStatus = recordPreamble(TSC, CPU);
    if (PreambleStatus == PreambleResult::InvalidBuffer)
      return returnBuffer();

    if (PreambleStatus == PreambleResult::NoChange &&
        UndoableFunctionEnters != 0 &&
        TSC - LastFunctionEntryTSC < CycleThreshold)
      return rewindRecords(FuncId, TSC, CPU);

    UndoableTailExits = UndoableFunctionEnters ? UndoableTailExits + 1 : 0;
    UndoableFunctionEnters = 0;
    auto Delta = TSC - LatestTSC;
    LatestTSC = TSC;
    return W.writeFunction(FDRLogWriter::FunctionRecordKind::TailExit,
                           mask(FuncId), Delta);
  }

  bool functionEnterArg(int32_t FuncId, uint64_t TSC, uint16_t CPU,
                        uint64_t Arg) XRAY_NEVER_INSTRUMENT {
    if (finalized() ||
        !prepareBuffer((2 * sizeof(MetadataRecord)) + sizeof(FunctionRecord)) ||
        recordPreamble(TSC, CPU) == PreambleResult::InvalidBuffer)
      return returnBuffer();

    auto Delta = TSC - LatestTSC;
    LatestTSC = TSC;
    LastFunctionEntryTSC = 0;
    UndoableFunctionEnters = 0;
    UndoableTailExits = 0;

    return W.writeFunctionWithArg(FDRLogWriter::FunctionRecordKind::EnterArg,
                                  mask(FuncId), Delta, Arg);
  }

  bool functionExit(int32_t FuncId, uint64_t TSC,
                    uint16_t CPU) XRAY_NEVER_INSTRUMENT {
    if (finalized() ||
        !prepareBuffer(sizeof(MetadataRecord) + sizeof(FunctionRecord)))
      return returnBuffer();

    auto PreambleStatus = recordPreamble(TSC, CPU);
    if (PreambleStatus == PreambleResult::InvalidBuffer)
      return returnBuffer();

    if (PreambleStatus == PreambleResult::NoChange &&
        UndoableFunctionEnters != 0 &&
        TSC - LastFunctionEntryTSC < CycleThreshold)
      return rewindRecords(FuncId, TSC, CPU);

    auto Delta = TSC - LatestTSC;
    LatestTSC = TSC;
    UndoableFunctionEnters = 0;
    UndoableTailExits = 0;
    return W.writeFunction(FDRLogWriter::FunctionRecordKind::Exit, mask(FuncId),
                           Delta);
  }

  bool customEvent(uint64_t TSC, uint16_t CPU, const void *Event,
                   int32_t EventSize) XRAY_NEVER_INSTRUMENT {
    if (finalized() ||
        !prepareBuffer((2 * sizeof(MetadataRecord)) + EventSize) ||
        recordPreamble(TSC, CPU) == PreambleResult::InvalidBuffer)
      return returnBuffer();

    auto Delta = TSC - LatestTSC;
    LatestTSC = TSC;
    UndoableFunctionEnters = 0;
    UndoableTailExits = 0;
    return W.writeCustomEvent(Delta, Event, EventSize);
  }

  bool typedEvent(uint64_t TSC, uint16_t CPU, uint16_t EventType,
                  const void *Event, int32_t EventSize) XRAY_NEVER_INSTRUMENT {
    if (finalized() ||
        !prepareBuffer((2 * sizeof(MetadataRecord)) + EventSize) ||
        recordPreamble(TSC, CPU) == PreambleResult::InvalidBuffer)
      return returnBuffer();

    auto Delta = TSC - LatestTSC;
    LatestTSC = TSC;
    UndoableFunctionEnters = 0;
    UndoableTailExits = 0;
    return W.writeTypedEvent(Delta, EventType, Event, EventSize);
  }

  bool flush() XRAY_NEVER_INSTRUMENT {
    if (finalized()) {
      returnBuffer(); // ignore result.
      return true;
    }
    return returnBuffer();
  }
};

} // namespace __xray

#endif // COMPILER-RT_LIB_XRAY_XRAY_FDR_CONTROLLER_H_