lib/XRay/FileHeaderReader.cpp

   1 //===- FileHeaderReader.cpp - XRay File Header Reader  --------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 #include "llvm/XRay/FileHeaderReader.h"
   9
  10 namespace llvm {
  11 namespace xray {
  12
  13 // Populates the FileHeader reference by reading the first 32 bytes of the file.
  14 Expected<XRayFileHeader> readBinaryFormatHeader(DataExtractor &HeaderExtractor,
  15                                                 uint64_t &OffsetPtr) {
  16   // FIXME: Maybe deduce whether the data is little or big-endian using some
  17   // magic bytes in the beginning of the file?
  18
  19   // First 32 bytes of the file will always be the header. We assume a certain
  20   // format here:
  21   //
  22   //   (2)   uint16 : version
  23   //   (2)   uint16 : type
  24   //   (4)   uint32 : bitfield
  25   //   (8)   uint64 : cycle frequency
  26   //   (16)  -      : padding
  27   XRayFileHeader FileHeader;
  28   auto PreReadOffset = OffsetPtr;
  29   FileHeader.Version = HeaderExtractor.getU16(&OffsetPtr);
  30   if (OffsetPtr == PreReadOffset)
  31     return createStringError(
  32         std::make_error_code(std::errc::invalid_argument),
  33         "Failed reading version from file header at offset %" PRId64 ".",
  34         OffsetPtr);
  35
  36   PreReadOffset = OffsetPtr;
  37   FileHeader.Type = HeaderExtractor.getU16(&OffsetPtr);
  38   if (OffsetPtr == PreReadOffset)
  39     return createStringError(
  40         std::make_error_code(std::errc::invalid_argument),
  41         "Failed reading file type from file header at offset %" PRId64 ".",
  42         OffsetPtr);
  43
  44   PreReadOffset = OffsetPtr;
  45   uint32_t Bitfield = HeaderExtractor.getU32(&OffsetPtr);
  46   if (OffsetPtr == PreReadOffset)
  47     return createStringError(
  48         std::make_error_code(std::errc::invalid_argument),
  49         "Failed reading flag bits from file header at offset %" PRId64 ".",
  50         OffsetPtr);
  51
  52   FileHeader.ConstantTSC = Bitfield & 1uL;
  53   FileHeader.NonstopTSC = Bitfield & 1uL << 1;
  54   PreReadOffset = OffsetPtr;
  55   FileHeader.CycleFrequency = HeaderExtractor.getU64(&OffsetPtr);
  56   if (OffsetPtr == PreReadOffset)
  57     return createStringError(
  58         std::make_error_code(std::errc::invalid_argument),
  59         "Failed reading cycle frequency from file header at offset %" PRId64
  60         ".",
  61         OffsetPtr);
  62
  63   std::memcpy(&FileHeader.FreeFormData,
  64               HeaderExtractor.getData().bytes_begin() + OffsetPtr, 16);
  65
  66   // Manually advance the offset pointer 16 bytes, after getting a raw memcpy
  67   // from the underlying data.
  68   OffsetPtr += 16;
  69   return std::move(FileHeader);
  70 }
  71
  72 } // namespace xray
  73 } // namespace llvm