[CSSPGO][llvm-profgen] Parse mmap events from perf script

[wlei]

Summary

This stack of changes introduces llvm-profgen utility which generates a profile data file from given perf script data files for sample-based PGO. It’s part of(not only) the CSSPGO work. Specifically to support context-sensitive with/without pseudo probe profile, it implements a series of functionalities including perf trace parsing, instruction symbolization, LBR stack/call frame stack unwinding, pseudo probe decoding, etc. Also high throughput is achieved by multiple levels of sample aggregation and compatible format with one stop is generated at the end. Please refer to: https://groups.google.com/g/llvm-dev/c/1p1rdYbL93s for the CSSPGO RFC.

As a starter, this change sets up an entry point by introducing PerfReader to load profiled binaries and perf traces(including perf events and perf samples). For the event, here it parses the mmap2 events from perf script to build the loader snaps, which is used to retrieve the image load address in the subsequent perf tracing parsing.

As described in llvm-profgen.rst, the tool being built aims to support multiple input perf data (preprocessed by perf script) as well as multiple input binary images. It should also support dynamic reload/unload shared objects by leveraging the loader snaps being built by this change

[wmi]

Lei, thanks for the patch.

[wmi]

llvm/docs/CommandGuide/llvm-profgen.rst

15

Please explain what SPGO represents here.

llvm/tools/llvm-profgen/llvm-profgen.cpp

72

It is a map from address to ProfiledBinary, how about using AddressBinaryMap?

117

Here it is may or may not?

129

Maybe use BinaryTable.insert instead of BinaryTable.find above and use the return value to check whether the binary has been loaded before, then you don't have to search the table another time here.

144–145

Here BinaryAddrMap needs to erase an entry before inserting a new one. I guess it is to support the case that a load image is unloaded and then reloaded at a different place. If that is correct, please add some comment to make it clear.

[shenhan]

llvm/docs/CommandGuide/llvm-profgen.rst

36

Sometimes, the profiled binary path as recorded in mmaps is different from the local binary's path. I understand then this will only use the "name" part to match.
But sometimes the name part is also different, then the match cannot proceed.

One possible improvement is when the binary provided has embed "build-id", this can query perfdata file to get the absolute path of the file with matching build id, and use that absolute path to match mmap events and this would be the most accurate match, what do you think?

[hoy]

llvm/docs/CommandGuide/llvm-profgen.rst

36

Thanks for the suggestion. A build-id list can be made as an additional input to the tool for an accurate lookup of the mmap events.

[mtrofin]

llvm/tools/llvm-profgen/llvm-profgen.cpp

28

(flyby comment) is it a "perfscript" or a "perftrace" - or maybe "perfdata" rather.

Also, probably "perf tool" not "perf script" in the description.

35

Path to profiled binary?

50

Nit: to help maintainability down the road, perhaps ensure primitive fields are initialized here - I realize they are init-ed in the ctor, but it's even easier to maintain things when def and init on the same line. Less typing for the ctor, too.

67

should this set IsLoaded to false?

also, why not assert(!IsLoaded); or rename to "ensureLoaded";

or - is there value in a ProfiledBinary that's not loadable? If not, how about:

• private ctor
• fields are const; no need for IsLoaded
• public static factory method returning a std::unique_ptr<ProfildBinary> that's null if loading fails.

that way, a reader knows they don't need to bother worrying about ProfiledBinaries that don't work - simpler overall state. wdyt?

75

best to initialize struct fields to avoid undefined values.

95

should this rather be Buffer->getBufferSize() > static_cast<size_t>(std::numeric_limits<uint32_t>::max())?

106

could P+1 be out of bounds?

138

I guess this can happen because the Event could reference other binaries than the interesting ones, correct? Could you add a comment here about this - i.e. that the event is intentionally dropped here.

141

why call load - why not just fetch the ProfiledBinary entry? Unless I'm missing something, the expected behavior is that first the user-provided binaries are loaded; and if that goes well, then the events for them are loaded. So at this point the ProfiledBinary should be there?

144–145

Naive question: that assumes no interesting events were collected when the image was loaded at the old address?

175

consider using an enum like:

enum EventIndex {

WholeLine = 0,
PID = 1,
BaseAddress = 2... (etc)

}

so then dereferencing Fields is more readable.

207

perhaps instead of 'run' something more specific, like "loadBinariesAndEvents".

223

probably can be done later just fine, but should the main be in its own file, so then this becomes a reusable library?

[wlei]

fix according to reviewers' suggestions

llvm/docs/CommandGuide/llvm-profgen.rst

15

@wmi Thanks for the helpful list of feedbacks. More description is added here

36

@shenhan Thanks for your suggestion. Do you mean I need to do parsing the binary to get the "build-id"(if it has), then take it as a key to query the perfdata in which it bonds the absolute patch with the build-id? If my understanding is right, I will try to do it later change.

llvm/tools/llvm-profgen/llvm-profgen.cpp

28

@mtrofin Thanks for your helpful list of suggestions!

(flyby comment) is it a "perfscript" or a "perftrace" - or maybe "perfdata" rather.

here we intentionally use "perfscript" but not "perfdata" because it's not the raw perfdata created by the perf record but the output by the perf script -i perf.data, this can avoid to call the cmd inside the code.

Also, probably "perf tool" not "perf script" in the description.

Here change the description of it

35

you mean to change the desc here? "Path" is added

50

Fixed!

72

Good suggestion

75

fixed!

95

Good catch

106

Yeah, it seems it's not used here, delete this!

117

Good catch, fixed

129

Good to know this, fixed!

138

Yes, comments added

144–145

yes , comments added

144–145

Not sure whether it will remain the same address, but here I think it will cover this case. or maybe you want me to check if the base address doesn't change then we can just drop this event?

175

fixed, thanks for the suggestion

207

Agree it's better to have a specific name. My concern is we do not only load binaries and mmp events here, we must also do parsing the sample line simultaneously to extract info for the LBR unwinder(see its children changes), also do check the perfscript type, so I just use a general name as an entry of those misc. Any thoughts about this?

223

Yeah, we separate PerfReader to other files in the following commit, please see its children changes.

[hoy]

llvm/tools/llvm-profgen/llvm-profgen.cpp

106

The underlying MemoryBuffer ensures there is always trailing \0 at the end.

[mtrofin]

llvm/tools/llvm-profgen/llvm-profgen.cpp

144–145

Sorry, what I meant was: as the events list gets traversed, say that for a while events corresponding to the current base address are captured; then the base address changes. What happens to the captured events?

[hoy]

llvm/tools/llvm-profgen/llvm-profgen.cpp

67

Asserting the function is only run once per binary is reasonable since all provided binaries are loaded as soon as the tool starts. The initial design allowed for a load on demand, i.e, when binaries are not provided via the command line option, the profiled binaries record by mmap events will be automatically loaded while processing the events. IsLoaded was introduced as a signal for that. However that complicated the tool and was not continued.

A load failure would result the tool to error and exit instead of returning a null object. Please see subsequent patch D89712.

[mtrofin]

llvm/tools/llvm-profgen/llvm-profgen.cpp

67

So then could the loading happen in the ctor, since failure to load => fast fail? Then the ProfiledBinary is known to be always loaded, and the only mutable field is the base address - to be clear, my suggestion is for simpler maintainability.

[hoy]

llvm/tools/llvm-profgen/llvm-profgen.cpp

144–145

The events come in order of time. The mmap events serve as a time stamp for all LBR and call stack events. Once a mmap event is processed, the binary load loaded address recorded will be updated and all subsequent LBR events will be processed against the updated base address.

[mtrofin]

llvm/tools/llvm-profgen/llvm-profgen.cpp

144–145

I see - thanks!

[hoy]

llvm/tools/llvm-profgen/llvm-profgen.cpp

67

I see your point now. Thanks for the suggestion. There could be a case that user-specified binary never participated in profiling, which means they are not included in the mmap events, and they should not be loaded and if they are, their load failure should not block the processing. However, that sounds a user responsibility. Moving the load into ctor time is reasonable to me. It is a cleaner design.

[wlei]

move load() to ctor of ProfiledBianry

[wlei]

delete useless ProfiledBinary ctor

[shenhan]

llvm/tools/llvm-profgen/llvm-profgen.cpp

204

One thought on using MemoryBuffer::getFileOrSTDIN (or other similar MemroyBuffer based file reading):

• there could be scalability issues when processing huge (10G+) files, because the way MemoryBuffer::getFileOrSTDIN reads files is it reads the whole content into memory (or do a mmap) in oneshot, this imposes a huge burden on memory io.

• for perf script output parsing, it is mostly line based - each line is processed and discarded, this suggests that a stream based processing is more suitable and could be much more efficient. A straightforward way (with lower level io operations) could be like this: std::ifstream fin(perf_script_filename); if (!fin.good()) { /* error */ } for (std::string line; std::getline(input, line); ) { parseEvent(line); }

• this way, the memory consumption is almost constant regardless of the inpurt perf script file.

What do you think?

[hoy]

llvm/tools/llvm-profgen/llvm-profgen.cpp

204

This sounds a good solution to me. The perf file easies goes very large for large application and long profiling runs where reducing memory footprint will be very helpful.

[wlei]

llvm/tools/llvm-profgen/llvm-profgen.cpp

204

@shenhan Thanks for your suggestion, having a constant memory consumption is great, let me change the code.

[wenlei]

llvm/docs/CommandGuide/llvm-profgen.rst

15

small nit: searching through the code base, seems like the canonical name is "sample-based profile guided optimizations", most notably from the help message of fprofile-sample-use, so let's be consistent.

llvm/tools/llvm-profgen/llvm-profgen.cpp

149

const line_iterator& ?

210

What about we pass in BinaryFilenames and PerfTraceFilenames as parameters to this function (or to ctor), instead of letting PerfReader coupled with command-line options directly. Then perhaps name it readFromInput(BinaryFilenames, PerfTraceFilenames).

[wlei]

Refactor to put PerfReader and ProfiledBinary into seperated files
Use stream based trace reader(TraceStream class)
some function renaming

[wmi]

LGTM.

llvm/tools/llvm-profgen/ErrorHandling.h

10

Please fix the clang-tidy warning.

23

Like the clang-tidy suggests, better change it to "const Twine&"

[wlei]

fix clang-tidy warning.

[wenlei]

LGTM.

[thakis]

llvm/test/tools/llvm-profgen/lit.local.cfg

7

Out of interest, why is this here? llvm-profgen is part of the llvm build and should always exist, right (…assuming you add it to LLVM_TEST_DEPENDS in llvm/test/CmakeLists.txt – is there a reason to not add it there?)? No other tool test has a check like this as far as I know.

[thakis]

llvm/test/tools/llvm-profgen/lit.local.cfg

7

Looks like it's in LLVM_TEST_DEPENDS nowadays. Maybe these two lines can go now?

[hoy]

llvm/test/tools/llvm-profgen/lit.local.cfg

7

Good point. Yes, with llvm-profgen included in LLVM_TEST_DEPENDS, it should always be rebuilt and available at test time. The two lines are unnecessary.

llvm/docs/CommandGuide/llvm-profgen.rst

+llvm-profgen - LLVM SPGO profile generation tool
+=================================
+
+.. program:: llvm-profgen
+
+SYNOPSIS
+--------
+
+:program:`llvm-profgen` [*commands*] [*options*]
+
+DESCRIPTION
+-----------
+
+The :program:`llvm-profgen` utility generates a profile data file 
+from given perf script data files for sampling-based profile-guided 
+optimization(SPGO).
+
+COMMANDS
+--------
+At least one of the following commands are required:
+
+.. option:: --perfscript=<string[,string,...]>
+
+  Path of perf-script trace created by Linux perf tool with `script` 
+  command(the raw perf.data should be profiled with -b).
+
+.. option:: --output=<string>
+
+  Path of the output profile file.
+
+OPTIONS
+-------
+:program:`llvm-profgen` supports the following options:
+
+.. option:: --binary=<string[,string,...]>
+
+  Path of the input profiled binary files. If no file path is specified, the
+  path of the actual profiled binaries will be used instead. 
+
+.. option:: --show-mmap
+
+  Print mmap events.

llvm/test/tools/llvm-profgen/lit.local.cfg

+import subprocess
+import lit.util
+
+config.suffixes = ['.test', '.ll', '.s', '.yaml']
+if not lit.util.which("llvm-profgen", config.llvm_tools_dir):
+  config.unsupported = True  

llvm/test/tools/llvm-profgen/mmapEvent.test

+; RUN: llvm-profgen --perfscript=%s --output=%t --show-mmap | FileCheck %s
+
+PERF_RECORD_MMAP2 2580483/2580483: [0x400000(0x1000) @ 0 103:01 539973862 1972407324]: r-xp /home/a.out
+PERF_RECORD_MMAP2 2580483/2580483: [0x7f2505b40000(0x224000) @ 0 08:04 19532214 4169021329]: r-xp /usr/lib64/ld-2.17.so
+PERF_RECORD_MMAP2 2580483/2580483: [0x7ffe88097000(0x1000) @ 0 00:00 0 0]: r-xp [vdso]
+PERF_RECORD_MMAP2 2580483/2580483: [0x7f2505d56000(0xa000) @ 0 08:04 19530021 4190740662]: r-xp /usr/lib64/perf_fopen_hook.so
+PERF_RECORD_MMAP2 2580483/2580483: [0x7f250593c000(0x204000) @ 0 08:04 19532229 3585508847]: r-xp /usr/lib64/libdl-2.17.so
+PERF_RECORD_MMAP2 2580483/2580483: [0x7f250556e000(0x3ce000) @ 0 08:04 19532221 4003737677]: r-xp /usr/lib64/libc-2.17.so
+PERF_RECORD_MMAP2 2580483/2580483: [0x7f2505358000(0x216000) @ 0 08:04 19534595 2609212015]: r-xp /usr/lib64/libz.so.1.2.7
+     7f2505b49811 0x7f2505b49811/0x7f2505b509f0/P/-/-/0  0x7f2505b4974c/0x7f2505b4975b/P/-/-/0  0x7f2505b49837/0x7f2505b49720/P/-/-/0  0x7f2505b50a5a/0x7f2505b49816/P/-/-/0  0x7f2505b50a27/0x7f2505b50a50/P/-/-/0  0x7f2505b50a36/0x7f2505b50a20/P/-/-/0  0x7f2505b59dd0/0x7f2505b50a34/P/-/-/0  0x7f2505b59db4/0x7f2505b59dc3/P/-/-/0  0x7f2505b50a2f/0x7f2505b59db0/P/-/-/0  0x7f2505b50a15/0x7f2505b50a29/P/-/-/0  0x7f2505b59dd0/0x7f2505b50a05/P/-/-/0  0x7f2505b59db4/0x7f2505b59dc3/P/-/-/0  0x7f2505b50a00/0x7f2505b59db0/P/-/-/0  0x7f2505b49811/0x7f2505b509f0/P/-/-/0  0x7f2505b4974c/0x7f2505b4975b/P/-/-/0  0x7f2505b4a08a/0x7f2505b496a0/P/-/-/0
+PERF_RECORD_MMAP2 2580483/2580483: [0x7f2505d56000(0x8000) @ 0 08:04 19530021 4190740662]: r-xp /usr/lib64/perf_fopen_hook.so
+           4006b1 0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0
+PERF_RECORD_MMAP2 2580483/2580483: [0x7f2505156000(0x202000) @ 0 103:01 539962022 734061270]: r-xp /home/hoy/test/dlopen/helper.so
+           4006b1 0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0  0x4006b1/0x4006a0/P/-/-/0
+PERF_RECORD_MMAP2 2580483/2580483: [0x7f2505156000(0x202000) @ 0 103:01 539962022 734061270]: r-xp /home/hoy/test/dlopen/helper.so
+
+
+; CHECK: Mmap: Binary /home/a.out loaded at 0x400000
+; CHECK: Mmap: Binary /usr/lib64/ld-2.17.so loaded at 0x7f2505b40000
+; CHECK: Mmap: Binary [vdso] loaded at 0x7ffe88097000
+; CHECK: Mmap: Binary /usr/lib64/perf_fopen_hook.so loaded at 0x7f2505d56000
+; CHECK: Mmap: Binary /usr/lib64/libdl-2.17.so loaded at 0x7f250593c000
+; CHECK: Mmap: Binary /usr/lib64/libc-2.17.so loaded at 0x7f250556e000
+; CHECK: Mmap: Binary /usr/lib64/libz.so.1.2.7 loaded at 0x7f2505358000
+; CHECK: Mmap: Binary /usr/lib64/perf_fopen_hook.so loaded at 0x7f2505d56000
+; CHECK: Mmap: Binary /home/hoy/test/dlopen/helper.so loaded at 0x7f2505156000
+; CHECK: Mmap: Binary /home/hoy/test/dlopen/helper.so loaded at 0x7f2505156000

llvm/tools/llvm-profgen/CMakeLists.txt

+set(LLVM_LINK_COMPONENTS
+  Core
+  ProfileData
+  Support
+  Symbolize
+  )
+
+add_llvm_tool(llvm-profgen
+  llvm-profgen.cpp
+  )

llvm/tools/llvm-profgen/ErrorHandling.h

+//===-- ErrorHandling.h - Error handler -------------------------*- 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_TOOLS_LLVM_PROGEN_ERRORHANDLING_H
+#define LLVM_TOOLS_LLVM_PROGEN_ERRORHANDLING_H
+
+#include "llvm/ADT/Twine.h"
+#include "llvm/Support/Errc.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/WithColor.h"
+#include <system_error>
+
+using namespace llvm;
+
+LLVM_ATTRIBUTE_NORETURN inline void
+exitWithError(Twine Message, StringRef Whence = StringRef(),
+              StringRef Hint = StringRef()) {
+  WithColor::error(errs(), "llvm-profgen");
+  if (!Whence.empty())
+    errs() << Whence.str() << ": ";
+  errs() << Message << "\n";
+  if (!Hint.empty())
+    WithColor::note() << Hint.str() << "\n";
+  ::exit(EXIT_FAILURE);
+}
+
+LLVM_ATTRIBUTE_NORETURN inline void
+exitWithError(std::error_code EC, StringRef Whence = StringRef()) {
+  exitWithError(EC.message(), Whence);
+}
+
+LLVM_ATTRIBUTE_NORETURN inline void exitWithError(Error E, StringRef Whence) {
+  exitWithError(errorToErrorCode(std::move(E)), Whence);
+}
+#endif

llvm/tools/llvm-profgen/LLVMBuild.txt

+;===- ./tools/llvm-profgen/LLVMBuild.txt ----------------------*- Conf -*--===;
+;
+; 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
+;
+;===------------------------------------------------------------------------===;
+;
+; This is an LLVMBuild description file for the components in this subdirectory.
+;
+; For more information on the LLVMBuild system, please see:
+;
+;   http://llvm.org/docs/LLVMBuild.html
+;
+;===------------------------------------------------------------------------===;
+
+[component_0]
+type = Tool
+name = llvm-profgen
+parent = Tools
+required_libraries = Support

llvm/tools/llvm-profgen/llvm-profgen.cpp

+//===- llvm-profgen.cpp - LLVM SPGO profile generation tool ---------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// llvm-profgen generates SPGO profiles from perf script ouput.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ErrorHandling.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/InitLLVM.h"
+#include "llvm/Support/LineIterator.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/Regex.h"
+#include <iostream>
+#include <list>
+#include <map>
+
+using namespace llvm;
+
+static cl::list<std::string> PerfTraceFilenames(
+    "perfscript", cl::value_desc("perfscript"), cl::OneOrMore,
+    llvm::cl::MiscFlags::CommaSeparated,
+    cl::desc("Path of perf-script trace created by Linux perf tool with "
+             "`script` command(the raw perf.data should be profiled with -b)"));
+
+static cl::list<std::string>
+    BinaryFilenames("binary", cl::value_desc("binary"), cl::ZeroOrMore,
+                    llvm::cl::MiscFlags::CommaSeparated,
+                    cl::desc("Path of profiled binary files"));
+
+static cl::opt<std::string> OutputFilename("output", cl::value_desc("output"),
+                                           cl::Required,
+                                           cl::desc("Output profile file"));
+
+static cl::opt<bool> ShowMmap("show-mmap", cl::Hidden, cl::init(false),
+                              cl::ZeroOrMore,
+                              cl::desc("Print binary load events."));
+
+namespace llvm {
+namespace sampleprof {
+
+class ProfiledBinary {
+  std::string Path;
+  mutable uint64_t BaseAddress = 0;
+
+public:
+  ProfiledBinary(StringRef Path) : Path(Path) { load(); }
+
+  const StringRef getPath() const { return Path; }
+  const StringRef getName() const { return llvm::sys::path::filename(Path); }
+  uint64_t getBaseAddress() const { return BaseAddress; }
+  void setBaseAddress(uint64_t Address) { BaseAddress = Address; }
+
+private:
+  void load() {
+    // TODO:
+  }
+};
+
+using BinaryMap = StringMap<ProfiledBinary>;
+using AddressBinaryMap = std::map<uint64_t, ProfiledBinary *>;
+
+struct MMapEvent {
+  pid_t PID = 0;
+  uint64_t BaseAddress = 0;
+  uint64_t Size = 0;
+  uint64_t Offset = 0;
+  StringRef BinaryPath;
+};
+
+class PerfReader {
+
+  BinaryMap BinaryTable;
+  AddressBinaryMap AddrToBinaryMap; // Used by address-based lookup.
+
+  /// Prepare a memory buffer for the contents of \p Filename.
+  ///
+  static std::unique_ptr<MemoryBuffer> setupMemoryBuffer(StringRef Filename) {
+    auto BufferOrErr = MemoryBuffer::getFileOrSTDIN(Filename);
+    if (std::error_code EC = BufferOrErr.getError())
+      exitWithError(EC, Filename);
+
+    auto Buffer = std::move(BufferOrErr.get());
+    if (Buffer->getBufferSize() >
+        static_cast<size_t>(std::numeric_limits<uint32_t>::max()))
+      exitWithError("file too large", Filename);
+
+    return Buffer;
+  }
+
+  /// Load symbols and disassemble the code of a give binary.
+  /// Also register the binary in the binary table.
+  ///
+  ProfiledBinary &loadBinary(const StringRef BinaryPath,
+                             bool AllowNameConflict = true) {
+    // The binary table is currently indexed by the binary name not the full
+    // binary path. This is because the user-given path may not match the one
+    // that was actually executed.
+    StringRef BinaryName = llvm::sys::path::filename(BinaryPath);
+
+    // Call to load the binary in the ctor of ProfiledBinary.
+    auto Ret = BinaryTable.insert({BinaryName, ProfiledBinary(BinaryPath)});
+
+    if (!Ret.second && !AllowNameConflict) {
+      std::string ErrorMsg = "Binary name conflict: " + BinaryPath.str() +
+                             " and " + Ret.first->second.getPath().str() +
+                             " \n";
+      exitWithError(ErrorMsg);
+    }
+
+    return Ret.first->second;
+  }
+
+  void updateBinaryAddress(const MMapEvent &Event) {
+    // Load the binary.
+    StringRef BinaryPath = Event.BinaryPath;
+    StringRef BinaryName = llvm::sys::path::filename(BinaryPath);
+
+    auto I = BinaryTable.find(BinaryName);
+    // Drop the event which doesn't belong to user-provided binaries
+    // or if its image is loaded at the same address
+    if (I == BinaryTable.end() ||
+        Event.BaseAddress == I->second.getBaseAddress())
+      return;
+
+    ProfiledBinary &Binary = I->second;
+
+    // A binary image could be uploaded and then reloaded at different
+    // place, so update the address map here
+    AddrToBinaryMap.erase(Binary.getBaseAddress());
+    AddrToBinaryMap[Event.BaseAddress] = &Binary;
+
+    // Update binary load address.
+    Binary.setBaseAddress(Event.BaseAddress);
+  }
+
+public:
+  PerfReader() {}
+
+  /// Parse a single line of a PERF_RECORD_MMAP2 event looking for a
+  /// mapping between the binary name and its memory layout.
+  ///
+  void parseMMap2Event(const line_iterator Line) {
+    // Parse a line like:
+    //  PERF_RECORD_MMAP2 2113428/2113428: [0x7fd4efb57000(0x204000) @ 0
+    //  08:04 19532229 3585508847]: r-xp /usr/lib64/libdl-2.17.so
+    constexpr static const char *const Pattern =
+        "PERF_RECORD_MMAP2 ([0-9]+)/[0-9]+: "
+        "\\[(0x[a-f0-9]+)\\((0x[a-f0-9]+)\\) @ "
+        "(0x[a-f0-9]+|0) .*\\]: [-a-z]+ (.*)";
+    // Field 0 - whole line
+    // Field 1 - PID
+    // Field 2 - base address
+    // Field 3 - mmapped size
+    // Field 4 - page offset
+    // Field 5 - binary path
+    enum EventIndex {
+      WHOLE_LINE = 0,
+      PID = 1,
+      BASE_ADDRESS = 2,
+      MMAPPED_SIZE = 3,
+      PAGE_OFFSET = 4,
+      BINARY_PATH = 5
+    };
+
+    Regex RegMmap2(Pattern);
+    SmallVector<StringRef, 6> Fields;
+    if (RegMmap2.match(*Line, &Fields)) {
+      MMapEvent Event;
+      Fields[PID].getAsInteger(10, Event.PID);
+      Fields[BASE_ADDRESS].getAsInteger(0, Event.BaseAddress);
+      Fields[MMAPPED_SIZE].getAsInteger(0, Event.Size);
+      Fields[PAGE_OFFSET].getAsInteger(0, Event.Offset);
+      Event.BinaryPath = Fields[BINARY_PATH];
+      updateBinaryAddress(Event);
+      if (ShowMmap) {
+        outs() << "Mmap: Binary " << Event.BinaryPath << " loaded at "
+               << format("0x%" PRIx64 ":", Event.BaseAddress) << " \n";
+      }
+    } else {
+      std::string ErrorMsg = "Cannot parse mmap event: Line " +
+                             Twine(Line.line_number()).str() + ": " +
+                             Line->str() + " \n";
+      exitWithError(ErrorMsg);
+    }
+  }
+
+  void parseEvent(line_iterator &Index) {
+    if (Index->startswith("PERF_RECORD_MMAP2"))
+      parseMMap2Event(Index);
+    ++Index;
+  }
+
+  void parseTrace(StringRef Filename) {
+    auto Buffer = setupMemoryBuffer(Filename);
+    line_iterator LineIt(*Buffer, /*SkipBlanks=*/false);
+    while (!LineIt.is_at_eof()) {
+      parseEvent(LineIt);
+    }
+  }
+
+  void run() {
+    // Load the binaries.
+    for (auto Filename : BinaryFilenames)
+      loadBinary(Filename, /*AllowNameConflict*/ false);
+
+    // Parse perf traces.
+    for (auto Filename : PerfTraceFilenames)
+      parseTrace(Filename);
+  }
+};
+
+} // end namespace sampleprof
+} // end namespace llvm
+
+using namespace sampleprof;
+
+int main(int argc, const char *argv[]) {
+  InitLLVM X(argc, argv);
+
+  cl::ParseCommandLineOptions(argc, argv, "llvm SPGO profile generator\n");
+
+  PerfReader Reader;
+  Reader.run();
+
+  return EXIT_SUCCESS;
+}