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
10namespace llvm {
11namespace xray {
12
13// Populates the FileHeader reference by reading the first 32 bytes of the file.
14Expected<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(offset_ptr: &OffsetPtr);
30 if (OffsetPtr == PreReadOffset)
31 return createStringError(
32 EC: std::make_error_code(e: std::errc::invalid_argument),
33 Fmt: "Failed reading version from file header at offset %" PRId64 ".",
34 Vals: OffsetPtr);
35
36 PreReadOffset = OffsetPtr;
37 FileHeader.Type = HeaderExtractor.getU16(offset_ptr: &OffsetPtr);
38 if (OffsetPtr == PreReadOffset)
39 return createStringError(
40 EC: std::make_error_code(e: std::errc::invalid_argument),
41 Fmt: "Failed reading file type from file header at offset %" PRId64 ".",
42 Vals: OffsetPtr);
43
44 PreReadOffset = OffsetPtr;
45 uint32_t Bitfield = HeaderExtractor.getU32(offset_ptr: &OffsetPtr);
46 if (OffsetPtr == PreReadOffset)
47 return createStringError(
48 EC: std::make_error_code(e: std::errc::invalid_argument),
49 Fmt: "Failed reading flag bits from file header at offset %" PRId64 ".",
50 Vals: OffsetPtr);
51
52 FileHeader.ConstantTSC = Bitfield & 1uL;
53 FileHeader.NonstopTSC = Bitfield & 1uL << 1;
54 PreReadOffset = OffsetPtr;
55 FileHeader.CycleFrequency = HeaderExtractor.getU64(offset_ptr: &OffsetPtr);
56 if (OffsetPtr == PreReadOffset)
57 return createStringError(
58 EC: std::make_error_code(e: std::errc::invalid_argument),
59 Fmt: "Failed reading cycle frequency from file header at offset %" PRId64
60 ".",
61 Vals: OffsetPtr);
62
63 std::memcpy(dest: &FileHeader.FreeFormData,
64 src: HeaderExtractor.getData().bytes_begin() + OffsetPtr, n: 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
74

source code of llvm/lib/XRay/FileHeaderReader.cpp