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diff --git a/include/llvm/DebugInfo/GSYM/Header.h b/include/llvm/DebugInfo/GSYM/Header.h
new file mode 100644
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+++ b/include/llvm/DebugInfo/GSYM/Header.h
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+//===- Header.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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_DEBUGINFO_GSYM_HEADER_H
+#define LLVM_DEBUGINFO_GSYM_HEADER_H
+
+#include "llvm/Support/Error.h"
+
+#include <cstddef>
+#include <cstdint>
+
+namespace llvm {
+class raw_ostream;
+class DataExtractor;
+
+namespace gsym {
+class FileWriter;
+
+constexpr uint32_t GSYM_MAGIC = 0x4753594d; // 'GSYM'
+constexpr uint32_t GSYM_CIGAM = 0x4d595347; // 'MYSG'
+constexpr uint32_t GSYM_VERSION = 1;
+constexpr size_t GSYM_MAX_UUID_SIZE = 20;
+
+/// The GSYM header.
+///
+/// The GSYM header is found at the start of a stand alone GSYM file, or as
+/// the first bytes in a section when GSYM is contained in a section of an
+/// executable file (ELF, mach-o, COFF).
+///
+/// The structure is encoded exactly as it appears in the structure definition
+/// with no gaps between members. Alignment should not change from system to
+/// system as the members were laid out so that they shouldn't align
+/// differently on different architectures.
+///
+/// When endianness of the system loading a GSYM file matches, the file can
+/// be mmap'ed in and a pointer to the header can be cast to the first bytes
+/// of the file (stand alone GSYM file) or section data (GSYM in a section).
+/// When endianness is swapped, the Header::decode() function should be used to
+/// decode the header.
+struct Header {
+  /// The magic bytes should be set to GSYM_MAGIC. This helps detect if a file
+  /// is a GSYM file by scanning the first 4 bytes of a file or section.
+  /// This value might appear byte swapped
+  uint32_t Magic;
+  /// The version can number determines how the header is decoded and how each
+  /// InfoType in FunctionInfo is encoded/decoded. As version numbers increase,
+  /// "Magic" and "Version" members should always appear at offset zero and 4
+  /// respectively to ensure clients figure out if they can parse the format.
+  uint16_t Version;
+  /// The size in bytes of each address offset in the address offsets table.
+  uint8_t AddrOffSize;
+  /// The size in bytes of the UUID encoded in the "UUID" member.
+  uint8_t UUIDSize;
+  /// The 64 bit base address that all address offsets in the address offsets
+  /// table are relative to. Storing a full 64 bit address allows our address
+  /// offsets table to be smaller on disk.
+  uint64_t BaseAddress;
+  /// The number of addresses stored in the address offsets table.
+  uint32_t NumAddresses;
+  /// The file relative offset of the start of the string table for strings
+  /// contained in the GSYM file. If the GSYM in contained in a stand alone
+  /// file this will be the file offset of the start of the string table. If
+  /// the GSYM is contained in a section within an executable file, this can
+  /// be the offset of the first string used in the GSYM file and can possibly
+  /// span one or more executable string tables. This allows the strings to
+  /// share string tables in an ELF or mach-o file.
+  uint32_t StrtabOffset;
+  /// The size in bytes of the string table. For a stand alone GSYM file, this
+  /// will be the exact size in bytes of the string table. When the GSYM data
+  /// is in a section within an executable file, this size can span one or more
+  /// sections that contains strings. This allows any strings that are already
+  /// stored in the executable file to be re-used, and any extra strings could
+  /// be added to another string table and the string table offset and size
+  /// can be set to span all needed string tables.
+  uint32_t StrtabSize;
+  /// The UUID of the original executable file. This is stored to allow
+  /// matching a GSYM file to an executable file when symbolication is
+  /// required. Only the first "UUIDSize" bytes of the UUID are valid. Any
+  /// bytes in the UUID value that appear after the first UUIDSize bytes should
+  /// be set to zero.
+  uint8_t UUID[GSYM_MAX_UUID_SIZE];
+
+  /// Check if a header is valid and return an error if anything is wrong.
+  ///
+  /// This function can be used prior to encoding a header to ensure it is
+  /// valid, or after decoding a header to ensure it is valid and supported.
+  ///
+  /// Check a correctly byte swapped header for errors:
+  ///   - check magic value
+  ///   - check that version number is supported
+  ///   - check that the address offset size is supported
+  ///   - check that the UUID size is valid
+  ///
+  /// \returns An error if anything is wrong in the header, or Error::success()
+  /// if there are no errors.
+  llvm::Error checkForError() const;
+
+  /// Decode an object from a binary data stream.
+  ///
+  /// \param Data The binary stream to read the data from. This object must
+  /// have the data for the object starting at offset zero. The data
+  /// can contain more data than needed.
+  ///
+  /// \returns A Header or an error describing the issue that was
+  /// encountered during decoding.
+  static llvm::Expected<Header> decode(DataExtractor &Data);
+
+  /// Encode this object into FileWriter stream.
+  ///
+  /// \param O The binary stream to write the data to at the current file
+  /// position.
+  ///
+  /// \returns An error object that indicates success or failure of the
+  /// encoding process.
+  llvm::Error encode(FileWriter &O) const;
+};
+
+bool operator==(const Header &LHS, const Header &RHS);
+raw_ostream &operator<<(raw_ostream &OS, const llvm::gsym::Header &H);
+
+} // namespace gsym
+} // namespace llvm
+
+#endif // #ifndef LLVM_DEBUGINFO_GSYM_HEADER_H