LLVM  10.0.0svn
FileHeaderReader.cpp
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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 //===----------------------------------------------------------------------===//
9 
10 namespace llvm {
11 namespace xray {
12 
13 // Populates the FileHeader reference by reading the first 32 bytes of the file.
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
uint16_t getU16(uint64_t *offset_ptr, Error *Err=nullptr) const
Extract a uint16_t value from *offset_ptr.
This class represents lattice values for constants.
Definition: AllocatorList.h:23
uint32_t getU32(uint64_t *offset_ptr, Error *Err=nullptr) const
Extract a uint32_t value from *offset_ptr.
StringRef getData() const
Get the data pointed to by this extractor.
Definition: DataExtractor.h:87
Expected< XRayFileHeader > readBinaryFormatHeader(DataExtractor &HeaderExtractor, uint64_t &OffsetPtr)
Convenience function for loading the file header given a data extractor at a specified offset...
std::error_code make_error_code(BitcodeError E)
Tagged union holding either a T or a Error.
Definition: yaml2obj.h:21
uint64_t CycleFrequency
The number of cycles per second for the CPU that produced the timestamp counter (TSC) values...
Definition: XRayRecord.h:45
uint16_t Type
A numeric identifier for the type of file this is.
Definition: XRayRecord.h:33
bool NonstopTSC
Whether the CPU that produced the timestamp counters (TSC) do not stop.
Definition: XRayRecord.h:40
const unsigned char * bytes_begin() const
Definition: StringRef.h:119
bool ConstantTSC
Whether the CPU that produced the timestamp counters (TSC) move at a constant rate.
Definition: XRayRecord.h:37
uint64_t getU64(uint64_t *offset_ptr, Error *Err=nullptr) const
Extract a uint64_t value from *offset_ptr.
XRay traces all have a header providing some top-matter information useful to help tools determine ho...
Definition: XRayRecord.h:27
Error createStringError(std::error_code EC, char const *Fmt, const Ts &... Vals)
Create formatted StringError object.
Definition: Error.h:1177
uint16_t Version
Version of the XRay implementation that produced this file.
Definition: XRayRecord.h:29