Add the ability to segment GSYM files.

[clayborg]

Summary

Some workflows can generate large GSYM files and sharding GSYM files into segments can help some performant workflows that can take advantage of smaller GSYM files. This patch add a new --segment-size option to llvm-gsymutil. This option can specify a rough size in bytes of how large each segment should be.

Segmented GSYM files contain only the strings and files that are needed for the FunctionInfo objects that are added to each shard. The output file path gets the first address of the first contained function info appended as a suffix to the filename. If a base address of an image is set in the GsymCreator, then all segments will use this same base address which allows lookups for symbolication to happen correctly when the image has been slid in memory.

Code has been addeed to refactor and re-use methods within the GsymCreator to allow for segments to be created easily and tested.

Example of segmenting GSYM files:

$ llvm-gsymutil --convert llvm-gsymutil.dSYM -o llvm-gsymutil.gsym --segment-size 10485760
$ ls -l llvm-gsymutil.gsym-*
-rw-r--r-- 1 gclayton staff 10485839 Feb 9 10:45 llvm-gsymutil.gsym-0x1000030c0
-rw-r--r-- 1 gclayton staff 10485765 Feb 9 10:45 llvm-gsymutil.gsym-0x100668888
-rw-r--r-- 1 gclayton staff 10485881 Feb 9 10:45 llvm-gsymutil.gsym-0x100c948b8
-rw-r--r-- 1 gclayton staff 10485954 Feb 9 10:45 llvm-gsymutil.gsym-0x101659e70
-rw-r--r-- 1 gclayton staff 10485792 Feb 9 10:45 llvm-gsymutil.gsym-0x1022b1dc0
-rw-r--r-- 1 gclayton staff 10485889 Feb 9 10:45 llvm-gsymutil.gsym-0x102a18b10
-rw-r--r-- 1 gclayton staff 10485893 Feb 9 10:45 llvm-gsymutil.gsym-0x1030b05d0
-rw-r--r-- 1 gclayton staff 10485802 Feb 9 10:45 llvm-gsymutil.gsym-0x1037caaac
-rw-r--r-- 1 gclayton staff 10485781 Feb 9 10:45 llvm-gsymutil.gsym-0x103e767a0
-rw-r--r-- 1 gclayton staff 10485832 Feb 9 10:45 llvm-gsymutil.gsym-0x10452d0d4
-rw-r--r-- 1 gclayton staff 10485782 Feb 9 10:45 llvm-gsymutil.gsym-0x104b93310
-rw-r--r-- 1 gclayton staff 6255785 Feb 9 10:45 llvm-gsymutil.gsym-0x10526bf34

[clayborg]

If anyone doesn't know the GSYM code that I added as reviewers, feel free to resign. I just did some blame lines on GSYM code to search for people that have made some fixes to the code since there aren't a lot of people that know the GSYM code!

[ayermolo]

llvm/include/llvm/DebugInfo/GSYM/GsymCreator.h

141

Maybe make it 64bit to future proof?

llvm/lib/DebugInfo/GSYM/GsymCreator.cpp

93

Maybe return an error like below? In case this is built with asserts disabled.

[avl]

llvm/lib/DebugInfo/GSYM/FunctionInfo.cpp

125

probably, name it a bit more descriptive?

llvm/lib/DebugInfo/GSYM/GsymCreator.cpp

450

[yinghuitan]

llvm/lib/DebugInfo/GSYM/GsymCreator.cpp

455

Instead of magic value 4, maybe sizeof(<type-of-offset-entry>) in case it is changed in future?

504–506

Is the lock only needed during accessing Funcs field? Maybe scope locking it instead of locking the entire function.

518–519

Shouldn't this be an error with meaning message instead of simply break and return success?

556

This is not changing per function, right? If so move outside of loop.

557

We should also detect outside loop at least SegmentSize > SegmentFuncInfosSize so that we are not creating dummy segment file with only header.

llvm/tools/llvm-gsymutil/llvm-gsymutil.cpp

322

The line is very long, maybe run clang-format against it.

[clayborg]

Address review comments:

• createSegment now can return an error if the segment size is too small
• added code to detect segment sizes that are too small to contain even a single function info
• added test code to test for small segment sizes

[clayborg]

llvm/lib/DebugInfo/GSYM/GsymCreator.cpp

504–506

This is correctly scoped right at the end of the function to only lock during Funcs modification and using the Funcs.back().

518–519

It isn't an error, createSegment returns NULL if there are no more functions which is ok.

518–519

I now return an expected to catch the error case where segment size is too small to contain a single function info.

556

It is changing per function, since each function info can add more strings and files to the GSYM file. calculateHeaderAndTableSize is fast to calculate. So this needs to stay here.

557

I will move this if statement after the copyFunctionInfo to ensure we always create a GSYM with at least one entry.

557

I modified the code to detect when no function infos have been emitted and return an error when I detect that. Also added a test.

[yinghuitan]

llvm/lib/DebugInfo/GSYM/GsymCreator.cpp

504–506

My original worry is compiler can hoist Guard to the beginning of the function causing the function scope locking. Now thinking about this, compiler shouldn't be doing that because it will have the side effect of changing the locking semantics. Still, I think it would be more explicit to add these into a sub-scope.

[ayermolo]

llvm/tools/llvm-gsymutil/llvm-gsymutil.cpp

112

Should we have some kind of sane default?

[chapuni]

llvm/lib/DebugInfo/GSYM/GsymCreator.cpp

126

MaxAddressOffset is used only here.

[uabelho]

I get the following with this patch

../unittests/DebugInfo/GSYM/GSYMTest.cpp:2492:12: error: call to deleted constructor of 'llvm::Error'
    return FinalizeErr;
           ^~~~~~~~~~~
../include/llvm/Support/Error.h:185:3: note: 'Error' has been explicitly marked deleted here
  Error(const Error &Other) = delete;
  ^
../include/llvm/Support/Error.h:492:18: note: passing argument to parameter 'Err' here
  Expected(Error Err)
                 ^
../unittests/DebugInfo/GSYM/GSYMTest.cpp:2499:12: error: call to deleted constructor of 'llvm::Error'
    return Err;
           ^~~
../include/llvm/Support/Error.h:185:3: note: 'Error' has been explicitly marked deleted here
  Error(const Error &Other) = delete;
  ^
../include/llvm/Support/Error.h:492:18: note: passing argument to parameter 'Err' here
  Expected(Error Err)
                 ^
2 errors generated.

Also seen here
https://lab.llvm.org/buildbot/#/builders/109/builds/58893

[dyung]

This change is causing multiple build bot failures in both the build and test stages:

https://lab.llvm.org/buildbot/#/builders/38/builds/10105
https://lab.llvm.org/buildbot/#/builders/192/builds/562
https://lab.llvm.org/buildbot/#/builders/109/builds/58893
https://lab.llvm.org/buildbot/#/builders/16/builds/44360
https://lab.llvm.org/buildbot/#/builders/247/builds/2095
https://lab.llvm.org/buildbot/#/builders/196/builds/27236
https://lab.llvm.org/buildbot/#/builders/54/builds/3714

llvm/include/llvm/DebugInfo/GSYM/FileWriter.h

public:
   /// \return The unsigned offset from the start of the file of the current
   ///         file position.
   uint64_t tell();
 
   llvm::raw_pwrite_stream &get_stream() {
     return OS;
   }
 
+  llvm::support::endianness getByteOrder() const { return ByteOrder; }
+
 private:
   FileWriter(const FileWriter &rhs) = delete;
   void operator=(const FileWriter &rhs) = delete;
 };
 
 } // namespace gsym
 } // namespace llvm
 
 #endif // LLVM_DEBUGINFO_GSYM_FILEWRITER_H

llvm/include/llvm/DebugInfo/GSYM/FunctionInfo.h

 /// }
 ///
 /// Where "N" is the number of tuples.
 struct FunctionInfo {
   AddressRange Range;
   uint32_t Name; ///< String table offset in the string table.
   std::optional<LineTable> OptLineTable;
   std::optional<InlineInfo> Inline;
+  /// If we encode a FunctionInfo during segmenting so we know its size, we can
+  /// cache that encoding here so we don't need to re-encode it when saving the
+  /// GSYM file.
+  SmallString<32> EncodingCache;
 
   FunctionInfo(uint64_t Addr = 0, uint64_t Size = 0, uint32_t N = 0)
       : Range(Addr, Addr + Size), Name(N) {}
 
   /// Query if a FunctionInfo has rich debug info.
   ///
   /// \returns A bool that indicates if this object has something else than
   /// range and name. When converting information from a symbol table and from
struct FunctionInfo {
   ///
   /// \param O The binary stream to write the data to at the current file
   /// position.
   ///
   /// \returns An error object that indicates failure or the offset of the
   /// function info that was successfully written into the stream.
   llvm::Expected<uint64_t> encode(FileWriter &O) const;
 
+  /// Encode this function info into the internal byte cache and return the size
+  /// in bytes.
+  ///
+  /// When segmenting GSYM files we need to know how big each FunctionInfo will
+  /// encode into so we can generate segments of the right size. We don't want
+  /// to have to encode a FunctionInfo twice, so we can cache the encoded bytes
+  /// and re-use then when calling FunctionInfo::encode(...).
+  ///
+  /// \returns The size in bytes of the FunctionInfo if it were to be encoded
+  /// into a byte stream.
+  uint64_t cacheEncoding();
 
   /// Lookup an address within a FunctionInfo object's data stream.
   ///
   /// Instead of decoding an entire FunctionInfo object when doing lookups,
   /// we can decode only the information we need from the FunctionInfo's data
   /// for the specific address. The lookup result information is returned as
   /// a LookupResult.
   ///

llvm/include/llvm/DebugInfo/GSYM/GsymCreator.h

 /// of FunctionInfo objects, see "llvm/DebugInfo/GSYM/FunctionInfo.h".
 class GsymCreator {
   // Private member variables require Mutex protections
   mutable std::mutex Mutex;
   std::vector<FunctionInfo> Funcs;
   StringTableBuilder StrTab;
   StringSet<> StringStorage;
   DenseMap<llvm::gsym::FileEntry, uint32_t> FileEntryToIndex;
+  // Needed for mapping string offsets back to the string stored in \a StrTab.
+  DenseMap<uint64_t, CachedHashStringRef> StringOffsetMap;
   std::vector<llvm::gsym::FileEntry> Files;
   std::vector<uint8_t> UUID;
   std::optional<AddressRanges> ValidTextRanges;
   AddressRanges Ranges;
   std::optional<uint64_t> BaseAddress;
   bool Finalized = false;
   bool Quiet;
 
+
+  /// Get the first function start address.
+  ///
+  /// \returns The start address of the first FunctionInfo or std::nullopt if
+  /// there are no function infos.
+  std::optional<uint64_t> getFirstFunctionAddress() const;
+
+  /// Get the last function address.
+  ///
+  /// \returns The start address of the last FunctionInfo or std::nullopt if
+  /// there are no function infos.
+  std::optional<uint64_t> getLastFunctionAddress() const;
+
+  /// Get the base address to use for this GSYM file.
+  ///
+  /// \returns The base address to put into the header and to use when creating
+  ///          the address offset table or std::nullpt if there are no valid
+  ///          function infos or if the base address wasn't specified.
+  std::optional<uint64_t> getBaseAddress() const;
+
+  /// Get the size of an address offset in the address offset table.
+  ///
+  /// GSYM files store offsets from the base address in the address offset table
+  /// and we store the size of the address offsets in the GSYM header. This
+  /// function will calculate the size in bytes of these address offsets based
+  /// on the current contents of the GSYM file.
+  ///
+  /// \returns The size in byets of the address offsets.
+  uint8_t getAddressOffsetSize() const;
+
+  /// Get the maximum address offset for the current address offset size.
+  ///
+  /// This is used when creating the address offset table to ensure we have
+  /// values that are in range so we don't end up truncating address offsets
+  /// when creating GSYM files as the code evolves.
+  ///
+  /// \returns The maximum address offset value that will be encoded into a GSYM
+  /// file.
+  uint64_t getMaxAddressOffset() const;
+
+  /// Calculate the byte size of the GSYM header and tables sizes.
+  ///
+  /// This function will calculate the exact size in bytes of the encocded GSYM
+  /// for the following items:
+  /// - The GSYM header
+  /// - The Address offset table
+  /// - The Address info offset table
+  /// - The file table
+  /// - The string table
+  ///
+  /// This is used to help split GSYM files into segments.
+  ///
+  /// \returns Size in bytes the GSYM header and tables.
+  uint64_t calculateHeaderAndTableSize() const;
+
+  /// Copy a FunctionInfo from the \a SrcGC GSYM creator into this creator.
+  ///
+  /// Copy the function info and only the needed files and strings and add a
+  /// converted FunctionInfo into this object. This is used to segment GSYM
+  /// files into separate files while only transferring the files and strings
+  /// that are needed from \a SrcGC.
+  ///
+  /// \param SrcGC The source gsym creator to copy from.
+  /// \param FuncInfoIdx The function info index within \a SrcGC to copy.
+  /// \returns The number of bytes it will take to encode the function info in
+  /// this GsymCreator. This helps calculate the size of the current GSYM
+  /// segment file.
+  uint64_t copyFunctionInfo(const GsymCreator &SrcGC, size_t FuncInfoIdx);
+
+  /// Copy a string from \a SrcGC into this object.
+  ///
+  /// Copy a string from \a SrcGC by string table offset into this GSYM creator.
+  /// If a string has already been copied, the uniqued string table offset will
+  /// be returned, otherwise the string will be copied and a unique offset will
+  /// be returned.
+  ///
+  /// \param SrcGC The source gsym creator to copy from.
+  /// \param StrOff The string table offset from \a SrcGC to copy.
+  /// \returns The new string table offset of the string within this object.
+  uint32_t copyString(const GsymCreator &SrcGC, uint32_t StrOff);
+
+  /// Copy a file from \a SrcGC into this object.
+  ///
+  /// Copy a file from \a SrcGC by file index into this GSYM creator. Files
+  /// consist of two string table entries, one for the directory and one for the
+  /// filename, this function will copy any needed strings ensure the file is
+  /// uniqued within this object. If a file already exists in this GSYM creator
+  /// the uniqued index will be returned, else the stirngs will be copied and
+  /// the new file index will be returned.
+  ///
+  /// \param SrcGC The source gsym creator to copy from.
+  /// \param FileIdx The 1 based file table index within \a SrcGC to copy. A
+  /// file index of zero will always return zero as the zero is a reserved file
+  /// index that means no file.
+  /// \returns The new file index of the file within this object.
+  uint32_t copyFile(const GsymCreator &SrcGC, uint32_t FileIdx);
+
+  /// Inserts a FileEntry into the file table.
+  ///
+  /// This is used to insert a file entry in a thread safe way into this object.
+  ///
+  /// \param FE A file entry object that contains valid string table offsets
+  /// from this object already.
+  uint32_t insertFileEntry(FileEntry FE);
+
+  /// Fixup any string and file references by updating any file indexes and
+  /// strings offsets in the InlineInfo parameter.
+  ///
+  /// When copying InlineInfo entries, we can simply make a copy of the object
+  /// and then fixup the files and strings for efficiency.
+  ///
+  /// \param SrcGC The source gsym creator to copy from.
+  /// \param II The inline info that contains file indexes and string offsets
+  /// that come from \a SrcGC. The entries will be updated by coping any files
+  /// and strings over into this object.
+  void fixupInlineInfo(const GsymCreator &SrcGC, InlineInfo &II);
+
+  /// Get the first function info address from this GSYM file.
+  ///
+  /// This is used to add a suffix to segmented GSYM files to indicate the first
+  /// address for the first function info within the file.
+  ///
+  /// \returns The first function info address.
+  uint64_t getFirstFunctionInfoAddress() const;
+
+  /// Save this GSYM file into segments that are roughly \a SegmentSize in size.
+  ///
+  /// When segemented GSYM files are saved to disk, they will use \a Path as a
+  /// prefix and then have the first function info address appended to the path
+  /// when each segment is saved. Each segmented GSYM file has a only the
+  /// strings and files that are needed to save the function infos that are in
+  /// each segment. These smaller files are easy to compress and download
+  /// separately and allow for efficient lookups with very large GSYM files and
+  /// segmenting them allows servers to download only the segments that are
+  /// needed.
+  ///
+  /// \param Path The path prefix to use when saving the GSYM files.
+  /// \param ByteOrder The endianness to use when saving the file.
+  /// \param SegmentSize The size in bytes to segment the GSYM file into.
+  llvm::Error saveSegments(StringRef Path,
+                           llvm::support::endianness ByteOrder,
+                           uint64_t SegmentSize) const;
+
 public:
   GsymCreator(bool Quiet = false);
 
   /// Save a GSYM file to a stand alone file.
   ///
   /// \param Path The file path to save the GSYM file to.
   /// \param ByteOrder The endianness to use when saving the file.
+  /// \param SegmentSize The size in bytes to segment the GSYM file into. If
+  ///                    this option is set this function will create N segments
+  ///                    that are all around \a SegmentSize bytes in size. This
+  ///                    allows a very large GSYM file to be broken up into
+  ///                    shards. Each GSYM file will have its own file table,
+  ///                    and string table that only have the files and strings
+  ///                    needed for the shared. If this argument has no value,
+  ///                    a single GSYM file that contains all function
+  ///                    information will be created.
   /// \returns An error object that indicates success or failure of the save.
-  llvm::Error save(StringRef Path, llvm::support::endianness ByteOrder) const;
+  llvm::Error save(StringRef Path, llvm::support::endianness ByteOrder,
+                   std::optional<uint64_t> SegmentSize = std::nullopt) const;
 
   /// Encode a GSYM into the file writer stream at the current position.
   ///
   /// \param O The stream to save the binary data to
   /// \returns An error object that indicates success or failure of the save.
   llvm::Error encode(FileWriter &O) const;
 
   /// Insert a string into the GSYM string table.
public:
   /// \param  Addr The address to use as the base address of the GSYM file
   ///              when it is saved to disk.
   void setBaseAddress(uint64_t Addr) {
     BaseAddress = Addr;
   }
 
   /// Whether the transformation should be quiet, i.e. not output warnings.
   bool isQuiet() const { return Quiet; }
+
+
+  /// Create a segmented GSYM creator starting with function info index
+  /// \a FuncIdx.
+  ///
+  /// This function will create a GsymCreator object that will encode into
+  /// roughly \a SegmentSize bytes and return it. It is used by the private
+  /// saveSegments(...) function and also is used by the GSYM unit tests to test
+  /// segmenting of GSYM files. The returned GsymCreator can be finalized and
+  /// encoded.
+  ///
+  /// \param [in] SegmentSize The size in bytes to roughly segment the GSYM file
+  /// into.
+  /// \param [in,out] FuncIdx The index of the first function info to encode
+  /// into the returned GsymCreator. This index will be updated so it can be
+  /// used in subsequent calls to this function to allow more segments to be
+  /// created.
+  /// \returns An expected unique pointer to a GsymCreator or an error. The
+  /// returned unique pointer can be NULL if there are no more functions to
+  /// encode.
+  llvm::Expected<std::unique_ptr<GsymCreator>>
+  createSegment(uint64_t SegmentSize, size_t &FuncIdx) const;
 };
 
 } // namespace gsym
 } // namespace llvm
 
 #endif // LLVM_DEBUGINFO_GSYM_GSYMCREATOR_H

llvm/include/llvm/DebugInfo/GSYM/LookupResult.h

struct LookupResult {
   /// the concrete function itself. This allows one address to generate
   /// multiple locations and allows unwinding of inline call stacks. The
   /// deepest inline function will appear at index zero in the source locations
   /// array, and the concrete function will appear at the end of the array.
   SourceLocations Locations;
   std::string getSourceFile(uint32_t Index) const;
 };
 
+inline bool operator==(const LookupResult &LHS, const LookupResult &RHS) {
+  if (LHS.LookupAddr != RHS.LookupAddr)
+    return false;
+  if (LHS.FuncRange != RHS.FuncRange)
+    return false;
+  if (LHS.FuncName != RHS.FuncName)
+    return false;
+  return LHS.Locations == RHS.Locations;
+}
+
 raw_ostream &operator<<(raw_ostream &OS, const LookupResult &R);
 
 } // namespace gsym
 } // namespace llvm
 
 #endif // LLVM_DEBUGINFO_GSYM_LOOKUPRESULT_H

llvm/lib/DebugInfo/GSYM/FunctionInfo.cpp

switch (IT) {
                                  "0x%8.8" PRIx64 ": unsupported InfoType %u",
                                  Offset-8, IT);
     }
     Offset += InfoLength;
   }
   return std::move(FI);
 }
 
-llvm::Expected<uint64_t> FunctionInfo::encode(FileWriter &O) const {
+uint64_t FunctionInfo::cacheEncoding() {
+  EncodingCache.clear();
+  if (!isValid())
+    return 0;
+  raw_svector_ostream OutStrm(EncodingCache);
+  FileWriter FW(OutStrm, support::endian::system_endianness());
+  llvm::Expected<uint64_t> Result = encode(FW);
+  if (!Result) {
+    EncodingCache.clear();
+    consumeError(Result.takeError());
+    return 0;
+  }
+  return EncodingCache.size();
+}
+
+llvm::Expected<uint64_t> FunctionInfo::encode(FileWriter &Out) const {
   if (!isValid())
     return createStringError(std::errc::invalid_argument,
         "attempted to encode invalid FunctionInfo object");
   // Align FunctionInfo data to a 4 byte alignment.
-  O.alignTo(4);
-  const uint64_t FuncInfoOffset = O.tell();
+  Out.alignTo(4);
+  const uint64_t FuncInfoOffset = Out.tell();
+  // Check if we have already encoded this function info into EncodingCache.
+  // This will be non empty when creating segmented GSYM files as we need to
+  // precompute exactly how big FunctionInfo objects encode into so we can
+  // accurately make segments of a specific size.
+  if (!EncodingCache.empty() &&
+      support::endian::system_endianness() == Out.getByteOrder()) {
+    // We already encoded this object, just write out the bytes.
+    Out.writeData(llvm::ArrayRef<uint8_t>((const uint8_t *)EncodingCache.data(),
+                                          EncodingCache.size()));
+    return FuncInfoOffset;
+  }
   // Write the size in bytes of this function as a uint32_t. This can be zero
   // if we just have a symbol from a symbol table and that symbol has no size.
-  O.writeU32(size());
+  Out.writeU32(size());
   // Write the name of this function as a uint32_t string table offset.
-  O.writeU32(Name);
+  Out.writeU32(Name);
 
   if (OptLineTable) {
-    O.writeU32(InfoType::LineTableInfo);
+    Out.writeU32(InfoType::LineTableInfo);
     // Write a uint32_t length as zero for now, we will fix this up after
     // writing the LineTable out with the number of bytes that were written.
-    O.writeU32(0);
-    const auto StartOffset = O.tell();
-    llvm::Error err = OptLineTable->encode(O, Range.start());
+    Out.writeU32(0);
+    const auto StartOffset = Out.tell();
+    llvm::Error err = OptLineTable->encode(Out, Range.start());
     if (err)
       return std::move(err);
-    const auto Length = O.tell() - StartOffset;
+    const auto Length = Out.tell() - StartOffset;
     if (Length > UINT32_MAX)
         return createStringError(std::errc::invalid_argument,
             "LineTable length is greater than UINT32_MAX");
     // Fixup the size of the LineTable data with the correct size.
-    O.fixup32(static_cast<uint32_t>(Length), StartOffset - 4);
+    Out.fixup32(static_cast<uint32_t>(Length), StartOffset - 4);
   }
 
   // Write out the inline function info if we have any and if it is valid.
   if (Inline) {
-    O.writeU32(InfoType::InlineInfo);
+    Out.writeU32(InfoType::InlineInfo);
     // Write a uint32_t length as zero for now, we will fix this up after
     // writing the LineTable out with the number of bytes that were written.
-    O.writeU32(0);
-    const auto StartOffset = O.tell();
-    llvm::Error err = Inline->encode(O, Range.start());
+    Out.writeU32(0);
+    const auto StartOffset = Out.tell();
+    llvm::Error err = Inline->encode(Out, Range.start());
     if (err)
       return std::move(err);
-    const auto Length = O.tell() - StartOffset;
+    const auto Length = Out.tell() - StartOffset;
     if (Length > UINT32_MAX)
         return createStringError(std::errc::invalid_argument,
             "InlineInfo length is greater than UINT32_MAX");
     // Fixup the size of the InlineInfo data with the correct size.
-    O.fixup32(static_cast<uint32_t>(Length), StartOffset - 4);
+    Out.fixup32(static_cast<uint32_t>(Length), StartOffset - 4);
   }
 
   // Terminate the data chunks with and end of list with zero size
-  O.writeU32(InfoType::EndOfList);
-  O.writeU32(0);
+  Out.writeU32(InfoType::EndOfList);
+  Out.writeU32(0);
   return FuncInfoOffset;
 }
 
 
 llvm::Expected<LookupResult> FunctionInfo::lookup(DataExtractor &Data,
                                                   const GsymReader &GR,
                                                   uint64_t FuncAddr,
                                                   uint64_t Addr) {

llvm/lib/DebugInfo/GSYM/GsymCreator.cpp

uint32_t GsymCreator::insertFile(StringRef Path, llvm::sys::path::Style Style) {
   llvm::StringRef directory = llvm::sys::path::parent_path(Path, Style);
   llvm::StringRef filename = llvm::sys::path::filename(Path, Style);
   // We must insert the strings first, then call the FileEntry constructor.
   // If we inline the insertString() function call into the constructor, the
   // call order is undefined due to parameter lists not having any ordering
   // requirements.
   const uint32_t Dir = insertString(directory);
   const uint32_t Base = insertString(filename);
-  FileEntry FE(Dir, Base);
+  return insertFileEntry(FileEntry(Dir, Base));
+}
 
+uint32_t GsymCreator::insertFileEntry(FileEntry FE) {
   std::lock_guard<std::mutex> Guard(Mutex);
   const auto NextIndex = Files.size();
   // Find FE in hash map and insert if not present.
   auto R = FileEntryToIndex.insert(std::make_pair(FE, NextIndex));
   if (R.second)
     Files.emplace_back(FE);
   return R.first->second;
 }
 
+uint32_t GsymCreator::copyFile(const GsymCreator &SrcGC, uint32_t FileIdx) {
+  // File index zero is reserved for a FileEntry with no directory and no
+  // filename. Any other file and we need to copy the strings for the directory
+  // and filename.
+  if (FileIdx == 0)
+    return 0;
+  const FileEntry SrcFE = SrcGC.Files[FileIdx];
+  // Copy the strings for the file and then add the newly converted file entry.
+  uint32_t Dir = StrTab.add(SrcGC.StringOffsetMap.find(SrcFE.Dir)->second);
+  uint32_t Base = StrTab.add(SrcGC.StringOffsetMap.find(SrcFE.Base)->second);
+  FileEntry DstFE(Dir, Base);
+  return insertFileEntry(DstFE);
+}
+
+
 llvm::Error GsymCreator::save(StringRef Path,
-                              llvm::support::endianness ByteOrder) const {
+                              llvm::support::endianness ByteOrder,
+                              std::optional<uint64_t> SegmentSize) const {
+  if (SegmentSize)
+    return saveSegments(Path, ByteOrder, *SegmentSize);
   std::error_code EC;
   raw_fd_ostream OutStrm(Path, EC);
   if (EC)
     return llvm::errorCodeToError(EC);
   FileWriter O(OutStrm, ByteOrder);
   return encode(O);
 }
 
 llvm::Error GsymCreator::encode(FileWriter &O) const {
   std::lock_guard<std::mutex> Guard(Mutex);
   if (Funcs.empty())
     return createStringError(std::errc::invalid_argument,
                              "no functions to encode");
   if (!Finalized)
     return createStringError(std::errc::invalid_argument,
                              "GsymCreator wasn't finalized prior to encoding");
 
   if (Funcs.size() > UINT32_MAX)
     return createStringError(std::errc::invalid_argument,
                              "too many FunctionInfos");
 
-  const uint64_t MinAddr =
-      BaseAddress ? *BaseAddress : Funcs.front().startAddress();
-  const uint64_t MaxAddr = Funcs.back().startAddress();
-  const uint64_t AddrDelta = MaxAddr - MinAddr;
+  std::optional<uint64_t> BaseAddress = getBaseAddress();
+  // Base address should be valid if we have any functions.
+  if (!BaseAddress)
+    return createStringError(std::errc::invalid_argument,
+                             "invalid base address");
   Header Hdr;
   Hdr.Magic = GSYM_MAGIC;
   Hdr.Version = GSYM_VERSION;
-  Hdr.AddrOffSize = 0;
+  Hdr.AddrOffSize = getAddressOffsetSize();
   Hdr.UUIDSize = static_cast<uint8_t>(UUID.size());
-  Hdr.BaseAddress = MinAddr;
+  Hdr.BaseAddress = *BaseAddress;
   Hdr.NumAddresses = static_cast<uint32_t>(Funcs.size());
   Hdr.StrtabOffset = 0; // We will fix this up later.
   Hdr.StrtabSize = 0;   // We will fix this up later.
   memset(Hdr.UUID, 0, sizeof(Hdr.UUID));
   if (UUID.size() > sizeof(Hdr.UUID))
     return createStringError(std::errc::invalid_argument,
                              "invalid UUID size %u", (uint32_t)UUID.size());
-  // Set the address offset size correctly in the GSYM header.
-  if (AddrDelta <= UINT8_MAX)
-    Hdr.AddrOffSize = 1;
-  else if (AddrDelta <= UINT16_MAX)
-    Hdr.AddrOffSize = 2;
-  else if (AddrDelta <= UINT32_MAX)
-    Hdr.AddrOffSize = 4;
-  else
-    Hdr.AddrOffSize = 8;
   // Copy the UUID value if we have one.
   if (UUID.size() > 0)
     memcpy(Hdr.UUID, UUID.data(), UUID.size());
   // Write out the header.
   llvm::Error Err = Hdr.encode(O);
   if (Err)
     return Err;
 
+  const uint64_t MaxAddressOffset = getMaxAddressOffset();
   // Write out the address offsets.
   O.alignTo(Hdr.AddrOffSize);
   for (const auto &FuncInfo : Funcs) {
     uint64_t AddrOffset = FuncInfo.startAddress() - Hdr.BaseAddress;
+    // Make sure we calculated the address offsets byte size correctly by
+    // verifying the current address offset is within ranges. We have seen bugs
+    // introduced when the code changes that can cause problems here so it is
+    // good to catch this during testing.
+    assert(AddrOffset <= MaxAddressOffset);
     switch (Hdr.AddrOffSize) {
     case 1:
       O.writeU8(static_cast<uint8_t>(AddrOffset));
       break;
     case 2:
       O.writeU16(static_cast<uint16_t>(AddrOffset));
       break;
     case 4:
llvm::Error GsymCreator::encode(FileWriter &O) const {
   if (NumFiles > UINT32_MAX)
     return createStringError(std::errc::invalid_argument, "too many files");
   O.writeU32(static_cast<uint32_t>(NumFiles));
   for (auto File : Files) {
     O.writeU32(File.Dir);
     O.writeU32(File.Base);
   }
 
-  // Write out the sting table.
+  // Write out the string table.
   const off_t StrtabOffset = O.tell();
   StrTab.write(O.get_stream());
   const off_t StrtabSize = O.tell() - StrtabOffset;
   std::vector<uint32_t> AddrInfoOffsets;
 
   // Write out the address infos for each function info.
   for (const auto &FuncInfo : Funcs) {
     if (Expected<uint64_t> OffsetOrErr = FuncInfo.encode(O))
if (auto Range =
       Funcs.back().Range = {Funcs.back().Range.start(), Range->end()};
     }
   }
   OS << "Pruned " << NumBefore - Funcs.size() << " functions, ended with "
      << Funcs.size() << " total\n";
   return Error::success();
 }
 
+uint32_t GsymCreator::copyString(const GsymCreator &SrcGC, uint32_t StrOff) {
+  // String offset at zero is always the empty string, no copying needed.
+  if (StrOff == 0)
+    return 0;
+  return StrTab.add(SrcGC.StringOffsetMap.find(StrOff)->second);
+}
+
 uint32_t GsymCreator::insertString(StringRef S, bool Copy) {
   if (S.empty())
     return 0;
 
   // The hash can be calculated outside the lock.
   CachedHashStringRef CHStr(S);
   std::lock_guard<std::mutex> Guard(Mutex);
   if (Copy) {
     // We need to provide backing storage for the string if requested
     // since StringTableBuilder stores references to strings. Any string
     // that comes from a section in an object file doesn't need to be
     // copied, but any string created by code will need to be copied.
     // This allows GsymCreator to be really fast when parsing DWARF and
     // other object files as most strings don't need to be copied.
     if (!StrTab.contains(CHStr))
       CHStr = CachedHashStringRef{StringStorage.insert(S).first->getKey(),
                                   CHStr.hash()};
   }
-  return StrTab.add(CHStr);
+  const uint32_t StrOff = StrTab.add(CHStr);
+  // Save a mapping of string offsets to the cached string reference in case
+  // we need to segment the GSYM file and copy string from one string table to
+  // another.
+  if (StringOffsetMap.count(StrOff) == 0)
+    StringOffsetMap.insert(std::make_pair(StrOff, CHStr));
+  return StrOff;
 }
 
 void GsymCreator::addFunctionInfo(FunctionInfo &&FI) {
   std::lock_guard<std::mutex> Guard(Mutex);
   Ranges.insert(FI.Range);
   Funcs.emplace_back(std::move(FI));
 }
 
if (ValidTextRanges)
     return ValidTextRanges->contains(Addr);
   return true; // No valid text ranges has been set, so accept all ranges.
 }
 
 bool GsymCreator::hasFunctionInfoForAddress(uint64_t Addr) const {
   std::lock_guard<std::mutex> Guard(Mutex);
   return Ranges.contains(Addr);
 }
+
+std::optional<uint64_t> GsymCreator::getFirstFunctionAddress() const {
+  if (Finalized && !Funcs.empty())
+    return std::optional<uint64_t>(Funcs.front().startAddress());
+  // This code gets used by the segmentation of GSYM files to help determine the
+  // size of the GSYM header while continually adding new FunctionInfo objects
+  // to this object, so we haven't finalized this object yet.
+  if (Ranges.empty())
+    return std::nullopt;
+  return std::optional<uint64_t>(Ranges.begin()->start());
+}
+
+std::optional<uint64_t> GsymCreator::getLastFunctionAddress() const {
+  if (Finalized && !Funcs.empty())
+    return std::optional<uint64_t>(Funcs.back().startAddress());
+  // This code gets used by the segmentation of GSYM files to help determine the
+  // size of the GSYM header while continually adding new FunctionInfo objects
+  // to this object, so we haven't finalized this object yet.
+  if (Ranges.empty())
+    return std::nullopt;
+  return std::optional<uint64_t>((Ranges.end() - 1)->end());
+}
+
+std::optional<uint64_t> GsymCreator::getBaseAddress() const {
+  if (BaseAddress)
+    return BaseAddress;
+  return getFirstFunctionAddress();
+}
+
+uint64_t GsymCreator::getMaxAddressOffset() const {
+  switch (getAddressOffsetSize()) {
+    case 1: return UINT8_MAX;
+    case 2: return UINT16_MAX;
+    case 4: return UINT32_MAX;
+    case 8: return UINT64_MAX;
+  }
+  llvm_unreachable("invalid address offset");
+}
+
+uint8_t GsymCreator::getAddressOffsetSize() const {
+  const std::optional<uint64_t> BaseAddress = getBaseAddress();
+  const std::optional<uint64_t> LastFuncAddr = getLastFunctionAddress();
+  if (BaseAddress && LastFuncAddr) {
+    const uint64_t AddrDelta = *LastFuncAddr - *BaseAddress;
+    if (AddrDelta <= UINT8_MAX)
+      return 1;
+    else if (AddrDelta <= UINT16_MAX)
+      return 2;
+    else if (AddrDelta <= UINT32_MAX)
+      return 4;
+    return 8;
+  }
+  return 1;
+}
+
+uint64_t GsymCreator::calculateHeaderAndTableSize() const {
+  uint64_t Size = sizeof(Header);
+  const size_t NumFuncs = Funcs.size();
+  // Add size of address offset table
+  Size += NumFuncs * getAddressOffsetSize();
+  // Add size of address info offsets which are 32 bit integers in version 1.
+  Size += NumFuncs * sizeof(uint32_t);
+  // Add file table size
+  Size += Files.size() * sizeof(FileEntry);
+  // Add string table size
+  Size += StrTab.getSize();
+
+  return Size;
+}
+
+// This function takes a InlineInfo class that was copy constructed from an
+// InlineInfo from the \a SrcGC and updates all members that point to strings
+// and files to point to strings and files from this GsymCreator.
+void GsymCreator::fixupInlineInfo(const GsymCreator &SrcGC, InlineInfo &II) {
+  II.Name = copyString(SrcGC, II.Name);
+  II.CallFile = copyFile(SrcGC, II.CallFile);
+  for (auto &ChildII: II.Children)
+    fixupInlineInfo(SrcGC, ChildII);
+}
+
+uint64_t GsymCreator::copyFunctionInfo(const GsymCreator &SrcGC, size_t FuncIdx) {
+  // To copy a function info we need to copy any files and strings over into
+  // this GsymCreator and then copy the function info and update the string
+  // table offsets to match the new offsets.
+  const FunctionInfo &SrcFI = SrcGC.Funcs[FuncIdx];
+  Ranges.insert(SrcFI.Range);
+
+  FunctionInfo DstFI;
+  DstFI.Range = SrcFI.Range;
+  DstFI.Name = copyString(SrcGC, SrcFI.Name);
+  // Copy the line table if there is one.
+  if (SrcFI.OptLineTable) {
+    // Copy the entire line table.
+    DstFI.OptLineTable = LineTable(SrcFI.OptLineTable.value());
+    // Fixup all LineEntry::File entries which are indexes in the the file table
+    // from SrcGC and must be converted to file indexes from this GsymCreator.
+    LineTable &DstLT = DstFI.OptLineTable.value();
+    const size_t NumLines = DstLT.size();
+    for (size_t I=0; I<NumLines; ++I) {
+      LineEntry &LE = DstLT.get(I);
+      LE.File = copyFile(SrcGC, LE.File);
+    }
+  }
+  // Copy the inline information if needed.
+  if (SrcFI.Inline) {
+    // Make a copy of the source inline information.
+    DstFI.Inline = SrcFI.Inline.value();
+    // Fixup all strings and files in the copied inline information.
+    fixupInlineInfo(SrcGC, *DstFI.Inline);
+  }
+  std::lock_guard<std::mutex> Guard(Mutex);
+  Funcs.push_back(DstFI);
+  return Funcs.back().cacheEncoding();
+}
+
+llvm::Error GsymCreator::saveSegments(StringRef Path,
+                                      llvm::support::endianness ByteOrder,
+                                      uint64_t SegmentSize) const {
+  if (SegmentSize == 0)
+    return createStringError(std::errc::invalid_argument,
+                             "invalid segment size zero");
+
+  size_t FuncIdx = 0;
+  const size_t NumFuncs = Funcs.size();
+  while (FuncIdx < NumFuncs) {
+    llvm::Expected<std::unique_ptr<GsymCreator>> ExpectedGC =
+        createSegment(SegmentSize, FuncIdx);
+    if (ExpectedGC) {
+      GsymCreator *GC = ExpectedGC->get();
+      if (GC == NULL)
+        break; // We had not more functions to encode.
+      raw_null_ostream ErrorStrm;
+      llvm::Error Err = GC->finalize(ErrorStrm);
+      if (Err)
+        return Err;
+      std::string SegmentedGsymPath;
+      raw_string_ostream SGP(SegmentedGsymPath);
+      std::optional<uint64_t> FirstFuncAddr = GC->getFirstFunctionAddress();
+      if (FirstFuncAddr) {
+        SGP << Path << "-" << llvm::format_hex(*FirstFuncAddr, 1);
+        SGP.flush();
+        Err = GC->save(SegmentedGsymPath, ByteOrder, std::nullopt);
+        if (Err)
+          return Err;
+      }
+    } else {
+      return ExpectedGC.takeError();
+    }
+  }
+  return Error::success();
+}
+
+llvm::Expected<std::unique_ptr<GsymCreator>>
+GsymCreator::createSegment(uint64_t SegmentSize, size_t &FuncIdx) const {
+  // No function entries, return empty unique pointer
+  if (FuncIdx >= Funcs.size())
+    return std::unique_ptr<GsymCreator>();
+
+  std::unique_ptr<GsymCreator> GC(new GsymCreator(/*Quiet=*/true));
+  // Set the base address if there is one.
+  if (BaseAddress)
+    GC->setBaseAddress(*BaseAddress);
+  // Copy the UUID value from this object into the new creator.
+  GC->setUUID(UUID);
+  const size_t NumFuncs = Funcs.size();
+  // Track how big the function infos are for the current segment so we can
+  // emit segments that are close to the requested size. It is quick math to
+  // determine the current header and tables sizes, so we can do that each loop.
+  uint64_t SegmentFuncInfosSize = 0;
+  for (; FuncIdx < NumFuncs; ++FuncIdx) {
+    const uint64_t HeaderAndTableSize = GC->calculateHeaderAndTableSize();
+    if (HeaderAndTableSize + SegmentFuncInfosSize >= SegmentSize) {
+      if (SegmentFuncInfosSize == 0)
+        return createStringError(std::errc::invalid_argument,
+                                 "a segment size of %" PRIu64 " is to small to "
+                                 "fit any function infos, specify a larger value",
+                                 SegmentSize);
+
+      break;
+    }
+    SegmentFuncInfosSize += alignTo(GC->copyFunctionInfo(*this, FuncIdx), 4);
+  }
+  return GC;
+}

llvm/tools/llvm-gsymutil/llvm-gsymutil.cpp

 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/TargetParser/Triple.h"
 #include <algorithm>
 #include <cstring>
 #include <inttypes.h>
 #include <iostream>
 #include <map>
+#include <optional>
 #include <string>
 #include <system_error>
 #include <vector>
 
 #include "llvm/DebugInfo/GSYM/DwarfTransformer.h"
 #include "llvm/DebugInfo/GSYM/FunctionInfo.h"
 #include "llvm/DebugInfo/GSYM/GsymCreator.h"
 #include "llvm/DebugInfo/GSYM/GsymReader.h"

 
 static opt<unsigned>
     NumThreads("num-threads",
                desc("Specify the maximum number (n) of simultaneous threads "
                     "to use when converting files to GSYM.\nDefaults to the "
                     "number of cores on the current machine."),
                cl::value_desc("n"), cat(ConversionOptions));
 
+static opt<uint64_t>
+    SegmentSize("segment-size",
+               desc("Specify the size in bytes of the size the final GSYM file "
+                    "should be segmented into. This allows GSYM files to be "
+                    "split across multiple files."),
+               cl::value_desc("s"), cat(ConversionOptions));
+
 static opt<bool>
     Quiet("quiet", desc("Do not output warnings about the debug information"),
           cat(ConversionOptions));
 
 static list<uint64_t> LookupAddresses("address",
                                       desc("Lookup an address in a GSYM file"),
                                       cl::value_desc("addr"),
                                       cat(LookupOptions));
static llvm::Error handleObjectFile(ObjectFile &Obj,
   // duplicate FunctionInfo entries where we might have found an entry from
   // debug info and also a symbol table entry from the object file.
   if (auto Err = Gsym.finalize(OS))
     return Err;
 
   // Save the GSYM file to disk.
   support::endianness Endian =
       Obj.makeTriple().isLittleEndian() ? support::little : support::big;
-  if (auto Err = Gsym.save(OutFile, Endian))
+
+  std::optional<uint64_t> OptSegmentSize;
+  if (SegmentSize > 0)
+    OptSegmentSize = SegmentSize;
+  if (auto Err = Gsym.save(OutFile, Endian, OptSegmentSize))
     return Err;
 
   // Verify the DWARF if requested. This will ensure all the info in the DWARF
   // can be looked up in the GSYM and that all lookups get matching data.
   if (Verify) {
     if (auto Err = DT.verify(OutFile))
       return Err;
   }

llvm/unittests/DebugInfo/GSYM/GSYMTest.cpp

TEST(GSYMTest, TestGsymCreatorMultipleSymbolsWithNoSize) {
   TestEncodeDecode(GC, llvm::support::little, GSYM_VERSION, AddrOffSize,
                    BaseAddr,
                    1, // NumAddresses
                    ArrayRef<uint8_t>(UUID));
   TestEncodeDecode(GC, llvm::support::big, GSYM_VERSION, AddrOffSize, BaseAddr,
                    1, // NumAddresses
                    ArrayRef<uint8_t>(UUID));
 }
+
+// Helper function to quickly create a FunctionInfo in a GsymCreator for testing.
+static void AddFunctionInfo(GsymCreator &GC, const char *FuncName,
+                            uint64_t FuncAddr, const char *SourcePath,
+                            const char *HeaderPath) {
+  FunctionInfo FI(FuncAddr, 0x30, GC.insertString(FuncName));
+  FI.OptLineTable = LineTable();
+  const uint32_t SourceFileIdx = GC.insertFile(SourcePath);
+  const uint32_t HeaderFileIdx = GC.insertFile(HeaderPath);
+  FI.OptLineTable->push(LineEntry(FuncAddr+0x00, SourceFileIdx, 5));
+  FI.OptLineTable->push(LineEntry(FuncAddr+0x10, HeaderFileIdx, 10));
+  FI.OptLineTable->push(LineEntry(FuncAddr+0x12, HeaderFileIdx, 20));
+  FI.OptLineTable->push(LineEntry(FuncAddr+0x14, HeaderFileIdx, 11));
+  FI.OptLineTable->push(LineEntry(FuncAddr+0x16, HeaderFileIdx, 30));
+  FI.OptLineTable->push(LineEntry(FuncAddr+0x18, HeaderFileIdx, 12));
+  FI.OptLineTable->push(LineEntry(FuncAddr+0x20, SourceFileIdx, 8));
+  FI.Inline = InlineInfo();
+
+  std::string InlineName1(FuncName); InlineName1.append("1");
+  std::string InlineName2(FuncName); InlineName2.append("2");
+  std::string InlineName3(FuncName); InlineName3.append("3");
+
+  FI.Inline->Name = GC.insertString(InlineName1);
+  FI.Inline->CallFile = SourceFileIdx;
+  FI.Inline->CallLine = 6;
+  FI.Inline->Ranges.insert(AddressRange(FuncAddr + 0x10, FuncAddr + 0x20));
+  InlineInfo Inline2;
+  Inline2.Name = GC.insertString(InlineName2);
+  Inline2.CallFile = HeaderFileIdx;
+  Inline2.CallLine = 33;
+  Inline2.Ranges.insert(AddressRange(FuncAddr + 0x12, FuncAddr + 0x14));
+  FI.Inline->Children.emplace_back(Inline2);
+  InlineInfo Inline3;
+  Inline3.Name = GC.insertString(InlineName3);
+  Inline3.CallFile = HeaderFileIdx;
+  Inline3.CallLine = 35;
+  Inline3.Ranges.insert(AddressRange(FuncAddr + 0x16, FuncAddr + 0x18));
+  FI.Inline->Children.emplace_back(Inline3);
+  GC.addFunctionInfo(std::move(FI));
+}
+
+// Finalize a GsymCreator, encode it and decode it and return the error or
+// GsymReader that was successfully decoded.
+static Expected<GsymReader> FinalizeEncodeAndDecode(GsymCreator &GC) {
+  Error FinalizeErr = GC.finalize(llvm::nulls());
+  if (FinalizeErr)
+    return FinalizeErr;
+  SmallString<1024> Str;
+  raw_svector_ostream OutStrm(Str);
+  const auto ByteOrder = support::endian::system_endianness();
+  FileWriter FW(OutStrm, ByteOrder);
+  llvm::Error Err = GC.encode(FW);
+  if (Err)
+    return Err;
+  return GsymReader::copyBuffer(OutStrm.str());
+}
+
+TEST(GSYMTest, TestGsymSegmenting) {
+  // Test creating a GSYM file with function infos and segment the information.
+  // We verify segmenting is working by creating a full GSYM and also by
+  // encoding multiple segments, then we verify that we get the same information
+  // when doing lookups on the full GSYM that was decoded from encoding the
+  // entire GSYM and also by decoding information from the segments themselves.
+  GsymCreator GC;
+  GC.setBaseAddress(0);
+  AddFunctionInfo(GC, "main", 0x1000, "/tmp/main.c", "/tmp/main.h");
+  AddFunctionInfo(GC, "foo", 0x2000, "/tmp/foo.c", "/tmp/foo.h");
+  AddFunctionInfo(GC, "bar", 0x3000, "/tmp/bar.c", "/tmp/bar.h");
+  AddFunctionInfo(GC, "baz", 0x4000, "/tmp/baz.c", "/tmp/baz.h");
+  Expected<GsymReader> GR = FinalizeEncodeAndDecode(GC);
+  ASSERT_THAT_EXPECTED(GR, Succeeded());
+  //GR->dump(outs());
+
+  // Create segmented GSYM files where each file contains 1 function. We will
+  // then test doing lookups on the "GR", or the full GSYM file and then test
+  // doing lookups on the GsymReader objects for each segment to ensure we get
+  // the exact same information. So after all of the code below we will have
+  // GsymReader objects that each contain one function. We name the creators
+  // and readers to match the one and only address they contain.
+  // GC1000 and GR1000 are for [0x1000-0x1030)
+  // GC2000 and GR2000 are for [0x2000-0x2030)
+  // GC3000 and GR3000 are for [0x3000-0x3030)
+  // GC4000 and GR4000 are for [0x4000-0x4030)
+
+  // Create the segments and verify that FuncIdx, an in/out parameter, gets
+  // updated as expected.
+  size_t FuncIdx = 0;
+  // Make sure we get an error if the segment size is too small to encode a
+  // single function info.
+  llvm::Expected<std::unique_ptr<GsymCreator>> GCError =
+      GC.createSegment(57, FuncIdx);
+  ASSERT_FALSE((bool)GCError);
+  checkError("a segment size of 57 is to small to fit any function infos, "
+             "specify a larger value", GCError.takeError());
+  // Make sure that the function index didn't get incremented when we didn't
+  // encode any values into the segmented GsymCreator.
+  ASSERT_EQ(FuncIdx, (size_t)0);
+
+  llvm::Expected<std::unique_ptr<GsymCreator>> GC1000 =
+      GC.createSegment(128, FuncIdx);
+  ASSERT_THAT_EXPECTED(GC1000, Succeeded());
+  ASSERT_EQ(FuncIdx, (size_t)1);
+  llvm::Expected<std::unique_ptr<GsymCreator>> GC2000 =
+      GC.createSegment(128, FuncIdx);
+  ASSERT_THAT_EXPECTED(GC2000, Succeeded());
+  ASSERT_EQ(FuncIdx, (size_t)2);
+  llvm::Expected<std::unique_ptr<GsymCreator>> GC3000 =
+      GC.createSegment(128, FuncIdx);
+  ASSERT_THAT_EXPECTED(GC3000, Succeeded());
+  ASSERT_EQ(FuncIdx, (size_t)3);
+  llvm::Expected<std::unique_ptr<GsymCreator>> GC4000 =
+      GC.createSegment(128, FuncIdx);
+  ASSERT_THAT_EXPECTED(GC4000, Succeeded());
+  ASSERT_EQ(FuncIdx, (size_t)4);
+  // When there are no function infos left to encode we expect to get  no error
+  // and get a NULL GsymCreator in the return value from createSegment.
+  llvm::Expected<std::unique_ptr<GsymCreator>> GCNull =
+      GC.createSegment(128, FuncIdx);
+  ASSERT_THAT_EXPECTED(GCNull, Succeeded());
+  ASSERT_TRUE(GC1000.get() != nullptr);
+  ASSERT_TRUE(GC2000.get() != nullptr);
+  ASSERT_TRUE(GC3000.get() != nullptr);
+  ASSERT_TRUE(GC4000.get() != nullptr);
+  ASSERT_TRUE(GCNull.get() == nullptr);
+  // Encode and decode the GsymReader for each segment and verify they succeed.
+  Expected<GsymReader> GR1000 = FinalizeEncodeAndDecode(*GC1000.get());
+  ASSERT_THAT_EXPECTED(GR1000, Succeeded());
+  Expected<GsymReader> GR2000 = FinalizeEncodeAndDecode(*GC2000.get());
+  ASSERT_THAT_EXPECTED(GR2000, Succeeded());
+  Expected<GsymReader> GR3000 = FinalizeEncodeAndDecode(*GC3000.get());
+  ASSERT_THAT_EXPECTED(GR3000, Succeeded());
+  Expected<GsymReader> GR4000 = FinalizeEncodeAndDecode(*GC4000.get());
+  ASSERT_THAT_EXPECTED(GR4000, Succeeded());
+
+  // Verify that all lookups match the range [0x1000-0x1030) when doing lookups
+  // in the GsymReader that contains all functions and from the segmented
+  // GsymReader in GR1000.
+  for (uint64_t Addr = 0x1000; Addr < 0x1030; ++Addr) {
+    // Lookup in the main GsymReader that contains all function infos
+    auto MainLR = GR->lookup(Addr);
+    ASSERT_THAT_EXPECTED(MainLR, Succeeded());
+    auto SegmentLR = GR1000->lookup(Addr);
+    ASSERT_THAT_EXPECTED(SegmentLR, Succeeded());
+    // Make sure the lookup results match.
+    EXPECT_EQ(MainLR.get(), SegmentLR.get());
+    // Make sure that the lookups on the functions that are not in the segment
+    // fail as expected.
+    ASSERT_THAT_EXPECTED(GR1000->lookup(0x2000), Failed());
+    ASSERT_THAT_EXPECTED(GR1000->lookup(0x3000), Failed());
+    ASSERT_THAT_EXPECTED(GR1000->lookup(0x4000), Failed());
+  }
+
+  // Verify that all lookups match the range [0x2000-0x2030) when doing lookups
+  // in the GsymReader that contains all functions and from the segmented
+  // GsymReader in GR2000.
+  for (uint64_t Addr = 0x2000; Addr < 0x2030; ++Addr) {
+    // Lookup in the main GsymReader that contains all function infos
+    auto MainLR = GR->lookup(Addr);
+    ASSERT_THAT_EXPECTED(MainLR, Succeeded());
+    auto SegmentLR = GR2000->lookup(Addr);
+    ASSERT_THAT_EXPECTED(SegmentLR, Succeeded());
+    // Make sure the lookup results match.
+    EXPECT_EQ(MainLR.get(), SegmentLR.get());
+    // Make sure that the lookups on the functions that are not in the segment
+    // fail as expected.
+    ASSERT_THAT_EXPECTED(GR2000->lookup(0x1000), Failed());
+    ASSERT_THAT_EXPECTED(GR2000->lookup(0x3000), Failed());
+    ASSERT_THAT_EXPECTED(GR2000->lookup(0x4000), Failed());
+
+  }
+
+  // Verify that all lookups match the range [0x3000-0x3030) when doing lookups
+  // in the GsymReader that contains all functions and from the segmented
+  // GsymReader in GR3000.
+  for (uint64_t Addr = 0x3000; Addr < 0x3030; ++Addr) {
+    // Lookup in the main GsymReader that contains all function infos
+    auto MainLR = GR->lookup(Addr);
+    ASSERT_THAT_EXPECTED(MainLR, Succeeded());
+    auto SegmentLR = GR3000->lookup(Addr);
+    ASSERT_THAT_EXPECTED(SegmentLR, Succeeded());
+    // Make sure the lookup results match.
+    EXPECT_EQ(MainLR.get(), SegmentLR.get());
+    // Make sure that the lookups on the functions that are not in the segment
+    // fail as expected.
+    ASSERT_THAT_EXPECTED(GR3000->lookup(0x1000), Failed());
+    ASSERT_THAT_EXPECTED(GR3000->lookup(0x2000), Failed());
+    ASSERT_THAT_EXPECTED(GR3000->lookup(0x4000), Failed());
+}
+
+  // Verify that all lookups match the range [0x4000-0x4030) when doing lookups
+  // in the GsymReader that contains all functions and from the segmented
+  // GsymReader in GR4000.
+  for (uint64_t Addr = 0x4000; Addr < 0x4030; ++Addr) {
+    // Lookup in the main GsymReader that contains all function infos
+    auto MainLR = GR->lookup(Addr);
+    ASSERT_THAT_EXPECTED(MainLR, Succeeded());
+    // Lookup in the GsymReader for that contains 0x4000
+    auto SegmentLR = GR4000->lookup(Addr);
+    ASSERT_THAT_EXPECTED(SegmentLR, Succeeded());
+    // Make sure the lookup results match.
+    EXPECT_EQ(MainLR.get(), SegmentLR.get());
+    // Make sure that the lookups on the functions that are not in the segment
+    // fail as expected.
+    ASSERT_THAT_EXPECTED(GR4000->lookup(0x1000), Failed());
+    ASSERT_THAT_EXPECTED(GR4000->lookup(0x2000), Failed());
+    ASSERT_THAT_EXPECTED(GR4000->lookup(0x3000), Failed());
+  }
+}