[llvm-exegesis] Add support for using memory annotations

[aidengrossman]

Summary

This patch adds in support for using memory annotations in the
subprocess execution mode.

[aidengrossman]

Rebase, cleanup tests, fix some function calls in unittests that I forgot to update after adjusting function signatures.

[aidengrossman]

Rebase + format

[aidengrossman]

Rebase

[courbet]

llvm/tools/llvm-exegesis/lib/Assembler.cpp

51–54

If we're always going to call these 4 in a sequence, let's have a single point of entry in ExegesisTarget

[aidengrossman]

Address reviewer feedback.

[aidengrossman]

Address reviewer feedback, rebase.

[aidengrossman]

Update preprocessor directives to prevent build failures on Linux platforms that don't have libpfm.

[aidengrossman]

Rebase

[aidengrossman]

Rebase

[aidengrossman]

Rebase

[courbet]

llvm/tools/llvm-exegesis/lib/Assembler.cpp

70

This might clobber the registers we just set up above.

[aidengrossman]

llvm/tools/llvm-exegesis/lib/Assembler.cpp

70

Yes. I have a TODO listed in https://reviews.llvm.org/D151023 for this function to push the current values of RAX, RDI, and RSI to the stack to save them and then pop them back after the operation. I was planning on doing this as a follow up after this landed once I actually needed to use those registers, but if this is a blocker I can get this fixed before landing.

[aidengrossman]

Rebase

[aidengrossman]

@courbet This patch is ready for review when you have some time. Thanks!

[courbet]

llvm/tools/llvm-exegesis/lib/Assembler.cpp

237

why else ? You could have both liveins and memory, right ? (same below)

Can you add a test ?

llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

41–42

please add a #define HAS_RSEQ for this to make the code clearer.

[aidengrossman]

Address first round of reviewer feedback.

[aidengrossman]

llvm/tools/llvm-exegesis/lib/Assembler.cpp

237

Ah, yep. I made it either/or here as it doesn't support passing the RDI (or different depending on ABI) scratch memory register, but there are definitely other uses for passing registers as live ins. Should be fixed in the next update. Thanks for the catch!

[aidengrossman]

Ignore the "in the next update" part of the last inline comment. I submitted it at the wrong point. @courbet This should be ready for another round of review when you get a chance. Thank you for all your patience with reviews on this stack!

[courbet]

llvm/test/tools/llvm-exegesis/X86/memory-annotations-livein.test

5

Can you add a comment to explain what the test checks ? Something like:

# This test check that we can use a combination of memory and register definitions.

Same for the other test.

[aidengrossman]

Closed by 9f80831f3627e800709e2434bbbd5bb179b1576e.

[Hahnfeld]

The tests aren't working on kernel 4.18 - are they missing a REQUIRES: exegesis-can-execute-in-subprocess?

[aidengrossman]

In D151025#4451358, @Hahnfeld wrote:

The tests aren't working on kernel 4.18 - are they missing a REQUIRES: exegesis-can-execute-in-subprocess?

Ah, yep. Sorry for not catching that. Hopefully 864787990091f61e0b2cdcc13bdcd1e3677a334f fixes that for you.

[MaskRay]

In D151025#4451279, @aidengrossman wrote:

Closed by 9f80831f3627e800709e2434bbbd5bb179b1576e.

It seems that you lost Differential Revision: in the commit. If you use arc (https://llvm.org/docs/Phabricator.html#requesting-a-review-via-the-command-line), arc amend should give you the reviewed-by information from @courbet

[aidengrossman]

Yes. I meant to add it on when cherry-picking from the branch containing these changes in my fork but forgot to add it in. I was doing it manually though and didn't realize arc amend would just do that. Thanks for the tip and sorry for the confusion there.

[foad]

@aidengrossman the two new lit tests are consistently failing on my machine, which is Ubuntu 22.04.2 but with kernel version 6.3.7. I get:

$ /home/jayfoad2/llvm-release/bin/llvm-exegesis -mtriple=x86_64-unknown-unknown -mode=latency -snippets-file=/home/jayfoad2/git/llvm-project/llvm/test/tools/llvm-exegesis/X86/latency/memory-annotations.s -execution-mode=subprocess
---
mode:            latency
key:
  instructions:
    - 'MOV64ri32 RAX i_0x2000'
    - 'MOV64rm RDI RAX i_0x1 %noreg i_0x0 %noreg'
  config:          ''
  register_initial_values: []
cpu_name:        znver4
llvm_triple:     x86_64-unknown-unknown
num_repetitions: 10000
measurements:    []
error:           'The benchmarking subprocess sent unexpected signal: Segmentation fault'
info:            ''
assembled_snippet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
...

I've tried running this under lldb but I can't catch the segfault, even if I use settings set target.process.follow-fork-mode child.

Any ideas what might be going wrong or how to debug it?

[aidengrossman]

I'm not sure what could be going wrong. I saw segmentation fault failures on one of the builders but after I added a check to the lit config to ensure that the subprocess mode was actually supported it went away. It might have something to do with security policies since this patch does some things that probably seem quite abnormal in regards to the process memory, but I might be completely wrong there with that assumption.

To debug you need to modify the code slightly as this patch uses ptrace, so lldb isn't able to grab the child process because there's already another process tracing it. You'll need to comment out the ptrace calls and then you should be able to get into the child process. I had a flag to do that on one of my development branches that maybe I should upstream at some point.

Once you have that setup, I've found it easiest to debug by breaking on a line right before the function call into the MCJITed test/test harness. Then I would single step through the assembly to see what was happening.

However, I understand this might be a pain to debug, so if you want me to disable the tests or add something to the lit config to ensure that these tests only run if memory annotations don't cause seg-faults while we can work on reproducing it without being too interruptive, I'm fine with doing that.

[MaskRay]

In D151025#4455327, @foad wrote:

@aidengrossman the two new lit tests are consistently failing on my machine, which is Ubuntu 22.04.2 but with kernel version 6.3.7. I get:

$ /home/jayfoad2/llvm-release/bin/llvm-exegesis -mtriple=x86_64-unknown-unknown -mode=latency -snippets-file=/home/jayfoad2/git/llvm-project/llvm/test/tools/llvm-exegesis/X86/latency/memory-annotations.s -execution-mode=subprocess
---
mode:            latency
key:
  instructions:
    - 'MOV64ri32 RAX i_0x2000'
    - 'MOV64rm RDI RAX i_0x1 %noreg i_0x0 %noreg'
  config:          ''
  register_initial_values: []
cpu_name:        znver4
llvm_triple:     x86_64-unknown-unknown
num_repetitions: 10000
measurements:    []
error:           'The benchmarking subprocess sent unexpected signal: Segmentation fault'
info:            ''
assembled_snippet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
...

I've tried running this under lldb but I can't catch the segfault, even if I use settings set target.process.follow-fork-mode child.

Any ideas what might be going wrong or how to debug it?

llvm-exegesis -mode=latency -snippets-file=memory-annotations-livein.s -execution-mode=subprocess has this 'The benchmarking subprocess sent unexpected signal: Segmentation fault' for me as well, but I haven't looked closely.
(sudo apt install libpfm4-dev so that LLVM_ENABLE_LIBPFM links the dependency)

[foad]

In D151025#4456730, @aidengrossman wrote:

I'm not sure what could be going wrong. I saw segmentation fault failures on one of the builders but after I added a check to the lit config to ensure that the subprocess mode was actually supported it went away. It might have something to do with security policies since this patch does some things that probably seem quite abnormal in regards to the process memory, but I might be completely wrong there with that assumption.

To debug you need to modify the code slightly as this patch uses ptrace, so lldb isn't able to grab the child process because there's already another process tracing it. You'll need to comment out the ptrace calls and then you should be able to get into the child process. I had a flag to do that on one of my development branches that maybe I should upstream at some point.

Once you have that setup, I've found it easiest to debug by breaking on a line right before the function call into the MCJITed test/test harness. Then I would single step through the assembly to see what was happening.

However, I understand this might be a pain to debug, so if you want me to disable the tests or add something to the lit config to ensure that these tests only run if memory annotations don't cause seg-faults while we can work on reproducing it without being too interruptive, I'm fine with doing that.

strace on the JITted part of the child process shows:

munmap(NULL, 140344954515456)           = 0
munmap(0x7fa49b29d000, 392533778432)    = 0
mmap(0x7fffffffe000, 4096, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED_NOREPLACE, 8, 0) = 0x7fffffffe000
mmap(0x2000, 4096, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED_NOREPLACE, 9, 0) = -1 EPERM (Operation not permitted)
ioctl(7, PERF_EVENT_IOC_RESET, PERF_IOC_FLAG_GROUP|0x2) = 0
--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0x2000} ---
+++ killed by SIGSEGV (core dumped) +++

i.e. the access to address 0x2000 fails because the mmap call failed with EPERM.

There is some discussion here about why you might get the "nonsensical" error EPERM if you try to map an address lower than mmap_min_addr: https://lore.kernel.org/all/[e-mail]/T/#u

And sure enough my system has mmap_min_addr set higher than 0x2000:

$ sysctl vm.mmap_min_addr
vm.mmap_min_addr = 65536

This setting comes from /etc/sysctl.d/10-zeropage.conf which seems to be an Ubuntu-specific change to the Debain procps package.

I have verified that sed -i s/8192/65536/ test/tools/llvm-exegesis/X86/latency/memory-annotations*.s fixes the tests for me.

[aidengrossman]

Interesting. I'm running Ubuntu 22.04 as well and running sysctl vm.mmap_min_addr for me also gives 65536, but I was doing all of my development inside of a privileged container which I assume was able to allocate memory at an address lower than that maybe due to permissions differences. It fails for me when I do a build outside a container. Thank you so much for debugging this! I'll get a patch up changing the addresses soon and hopefully that fixes the test failures.

[aidengrossman]

46f42e2ee59ac5ff7b153648e30273e499f7b7e3 should fix the issue. Please let me know if there are any further issues.

[foad]

Interesting. I'm running Ubuntu 22.04 as well and running sysctl vm.mmap_min_addr for me also gives 65536, but I was doing all of my development inside of a privileged container which I assume was able to allocate memory at an address lower than that maybe due to permissions differences.

Yeah, I saw something about the limit not being enforced for processes with CAP_SYS_RAWIO, so maybe that was the difference.

Anyway your fix works for me - thanks!

llvm/test/tools/llvm-exegesis/X86/latency/memory-annotations.s

+# REQUIRES: exegesis-can-execute-x86_64, exegesis-can-measure-latency, x86_64-linux
+
+# RUN: llvm-exegesis -mtriple=x86_64-unknown-unknown -mode=latency -snippets-file=%s -execution-mode=subprocess | FileCheck %s
+# RUN: llvm-exegesis -mtriple=x86_64-unknown-unknown -mode=latency -snippets-file=%s -execution-mode=subprocess -repetition-mode=loop | FileCheck %s
+
+# CHECK: measurements:
+# CHECK-NEXT: value: {{.*}}, per_snippet_value: {{.*}}
+
+# LLVM-EXEGESIS-MEM-DEF test1 4096 2147483647
+# LLVM-EXEGESIS-MEM-MAP test1 8192
+
+movq $8192, %rax
+movq (%rax), %rdi

llvm/test/tools/llvm-exegesis/X86/memory-annotations-livein.test

+# REQUIRES: exegesis-can-execute-x86_64, exegesis-can-measure-latency, x86_64-linux
+
+# RUN: llvm-exegesis -mtriple=x86_64-unknown-unknown -mode=latency -snippets-file=%s -execution-mode=subprocess | FileCheck %s
+
+# CHECK: measurements:
+# CHECK-NEXT: value: {{.*}}, per_snippet_value: {{.*}}
+
+# LLVM-EXEGESIS-MEM-DEF test1 4096 2147483647
+# LLVM-EXEGESIS-MEM-MAP test1 8192
+# LLVM-EXEGESIS-LIVEIN R14
+
+movq $8192, %rax
+movq %r14, (%rax)

llvm/tools/llvm-exegesis/lib/Assembler.h

 class BasicBlockFiller {
 public:
   BasicBlockFiller(MachineFunction &MF, MachineBasicBlock *MBB,
                    const MCInstrInfo *MCII);
 
   void addInstruction(const MCInst &Inst, const DebugLoc &DL = DebugLoc());
   void addInstructions(ArrayRef<MCInst> Insts, const DebugLoc &DL = DebugLoc());
 
-  void addReturn(const DebugLoc &DL = DebugLoc());
+  void addReturn(const ExegesisTarget &ET, bool SubprocessCleanup,
+                 const DebugLoc &DL = DebugLoc());
 
   MachineFunction &MF;
   MachineBasicBlock *const MBB;
   const MCInstrInfo *const MCII;
 };
 
 // Helper to fill in a function.
 class FunctionFiller {

 // Creates a temporary `void foo(char*)` function containing the provided
 // Instructions. Runs a set of llvm Passes to provide correct prologue and
 // epilogue. Once the MachineFunction is ready, it is assembled for TM to
 // AsmStream, the temporary function is eventually discarded.
 Error assembleToStream(const ExegesisTarget &ET,
                        std::unique_ptr<LLVMTargetMachine> TM,
                        ArrayRef<unsigned> LiveIns,
                        ArrayRef<RegisterValue> RegisterInitialValues,
-                       const FillFunction &Fill, raw_pwrite_stream &AsmStream);
+                       const FillFunction &Fill, raw_pwrite_stream &AsmStreamm,
+                       const BenchmarkKey &Key,
+                       bool GenerateMemoryInstructions);
 
 // Creates an ObjectFile in the format understood by the host.
 // Note: the resulting object keeps a copy of Buffer so it can be discarded once
 // this function returns.
 object::OwningBinary<object::ObjectFile> getObjectFromBuffer(StringRef Buffer);
 
 // Loads the content of Filename as on ObjectFile and returns it.
 object::OwningBinary<object::ObjectFile> getObjectFromFile(StringRef Filename);

llvm/tools/llvm-exegesis/lib/Assembler.cpp

 //===-- Assembler.cpp -------------------------------------------*- 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
 //
 //===----------------------------------------------------------------------===//
 
 #include "Assembler.h"
 
 #include "SnippetRepetitor.h"
+#include "SubprocessMemory.h"
 #include "Target.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/CodeGen/FunctionLoweringInfo.h"
 #include "llvm/CodeGen/GlobalISel/CallLowering.h"
 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/TargetInstrInfo.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/ExecutionEngine/SectionMemoryManager.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/Support/Alignment.h"
 #include "llvm/Support/MemoryBuffer.h"
 
+#ifdef HAVE_LIBPFM
+#include "perfmon/perf_event.h"
+#endif // HAVE_LIBPFM
+
 namespace llvm {
 namespace exegesis {
 
 static constexpr const char ModuleID[] = "ExegesisInfoTest";
 static constexpr const char FunctionID[] = "foo";
 static const Align kFunctionAlignment(4096);
 
 // Fills the given basic block with register setup code, and returns true if
 // all registers could be setup correctly.
 static bool generateSnippetSetupCode(
     const ExegesisTarget &ET, const MCSubtargetInfo *const MSI,
-    ArrayRef<RegisterValue> RegisterInitialValues, BasicBlockFiller &BBF) {
+    ArrayRef<RegisterValue> RegisterInitialValues, BasicBlockFiller &BBF,
+    const BenchmarkKey &Key, bool GenerateMemoryInstructions) {
   bool IsSnippetSetupComplete = true;
+  if (GenerateMemoryInstructions) {
+    BBF.addInstructions(ET.generateMemoryInitialSetup());
+    for (const MemoryMapping &MM : Key.MemoryMappings) {
+      BBF.addInstructions(ET.generateMmap(
+          MM.Address, Key.MemoryValues.at(MM.MemoryValueName).SizeBytes,
+          ET.getAuxiliaryMemoryStartAddress() +
+              sizeof(int) * (Key.MemoryValues.at(MM.MemoryValueName).Index +
+                             SubprocessMemory::AuxiliaryMemoryOffset)));
+    }
+    BBF.addInstructions(ET.setStackRegisterToAuxMem());
+  }
   for (const RegisterValue &RV : RegisterInitialValues) {
     // Load a constant in the register.
     const auto SetRegisterCode = ET.setRegTo(*MSI, RV.Register, RV.Value);
     if (SetRegisterCode.empty())
       IsSnippetSetupComplete = false;
     BBF.addInstructions(SetRegisterCode);
   }
+  if (GenerateMemoryInstructions) {
+#ifdef HAVE_LIBPFM
+    BBF.addInstructions(ET.configurePerfCounter(PERF_EVENT_IOC_RESET, true));
+#endif // HAVE_LIBPFM
+  }
   return IsSnippetSetupComplete;
 }
 
 // Small utility function to add named passes.
 static bool addPass(PassManagerBase &PM, StringRef PassName,
                     TargetPassConfig &TPC) {
   const PassRegistry *PR = PassRegistry::getPassRegistry();
   const PassInfo *PI = PR->getPassInfo(PassName);

 }
 
 void BasicBlockFiller::addInstructions(ArrayRef<MCInst> Insts,
                                        const DebugLoc &DL) {
   for (const MCInst &Inst : Insts)
     addInstruction(Inst, DL);
 }
 
-void BasicBlockFiller::addReturn(const DebugLoc &DL) {
+void BasicBlockFiller::addReturn(const ExegesisTarget &ET,
+                                 bool SubprocessCleanup, const DebugLoc &DL) {
+  // Insert cleanup code
+  if (SubprocessCleanup) {
+#ifdef HAVE_LIBPFM
+    addInstructions(ET.configurePerfCounter(PERF_EVENT_IOC_DISABLE, false));
+#endif // HAVE_LIBPFM
+#ifdef __linux__
+    addInstructions(ET.generateExitSyscall(0));
+#endif // __linux__
+  }
   // Insert the return code.
   const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
   if (TII->getReturnOpcode() < TII->getNumOpcodes()) {
     BuildMI(MBB, DL, TII->get(TII->getReturnOpcode()));
   } else {
     MachineIRBuilder MIB(MF);
     MIB.setMBB(*MBB);
 
BitVector getFunctionReservedRegs(const TargetMachine &TM) {
   // Saving reserved registers for client.
   return MF.getSubtarget().getRegisterInfo()->getReservedRegs(MF);
 }
 
 Error assembleToStream(const ExegesisTarget &ET,
                        std::unique_ptr<LLVMTargetMachine> TM,
                        ArrayRef<unsigned> LiveIns,
                        ArrayRef<RegisterValue> RegisterInitialValues,
-                       const FillFunction &Fill, raw_pwrite_stream &AsmStream) {
+                       const FillFunction &Fill, raw_pwrite_stream &AsmStream,
+                       const BenchmarkKey &Key,
+                       bool GenerateMemoryInstructions) {
   auto Context = std::make_unique<LLVMContext>();
   std::unique_ptr<Module> Module =
       createModule(Context, TM->createDataLayout());
   auto MMIWP = std::make_unique<MachineModuleInfoWrapperPass>(TM.get());
   MachineFunction &MF = createVoidVoidPtrMachineFunction(
       FunctionID, Module.get(), &MMIWP.get()->getMMI());
   MF.ensureAlignment(kFunctionAlignment);
 
   // We need to instruct the passes that we're done with SSA and virtual
   // registers.
   auto &Properties = MF.getProperties();
   Properties.set(MachineFunctionProperties::Property::NoVRegs);
   Properties.reset(MachineFunctionProperties::Property::IsSSA);
   Properties.set(MachineFunctionProperties::Property::NoPHIs);
 
   for (const unsigned Reg : LiveIns)
     MF.getRegInfo().addLiveIn(Reg);
 
+  if (GenerateMemoryInstructions) {
+    for (const unsigned Reg : ET.getArgumentRegisters())
+      MF.getRegInfo().addLiveIn(Reg);
+    // Add a live in for registers that need saving so that the machine verifier
+    // doesn't fail if the register is never defined.
+    for (const unsigned Reg : ET.getRegistersNeedSaving())
+      MF.getRegInfo().addLiveIn(Reg);
+  }
+
   std::vector<unsigned> RegistersSetUp;
   for (const auto &InitValue : RegisterInitialValues) {
     RegistersSetUp.push_back(InitValue.Register);
   }
   FunctionFiller Sink(MF, std::move(RegistersSetUp));
   auto Entry = Sink.getEntry();
+
   for (const unsigned Reg : LiveIns)
     Entry.MBB->addLiveIn(Reg);
 
+  if (GenerateMemoryInstructions) {
+    for (const unsigned Reg : ET.getArgumentRegisters())
+      Entry.MBB->addLiveIn(Reg);
+    // Add a live in for registers that need saving so that the machine verifier
+    // doesn't fail if the register is never defined.
+    for (const unsigned Reg : ET.getRegistersNeedSaving())
+      Entry.MBB->addLiveIn(Reg);
+  }
+
   const bool IsSnippetSetupComplete = generateSnippetSetupCode(
-      ET, TM->getMCSubtargetInfo(), RegisterInitialValues, Entry);
+      ET, TM->getMCSubtargetInfo(), RegisterInitialValues, Entry, Key,
+      GenerateMemoryInstructions);
 
   // If the snippet setup is not complete, we disable liveliness tracking. This
   // means that we won't know what values are in the registers.
   // FIXME: this should probably be an assertion.
   if (!IsSnippetSetupComplete)
     Properties.reset(MachineFunctionProperties::Property::TracksLiveness);
 
   Fill(Sink);

llvm/tools/llvm-exegesis/lib/BenchmarkRunner.h

protected:
   const Benchmark::ModeE Mode;
   const BenchmarkPhaseSelectorE BenchmarkPhaseSelector;
   const ExecutionModeE ExecutionMode;
 
 private:
   virtual Expected<std::vector<BenchmarkMeasure>>
   runMeasurements(const FunctionExecutor &Executor) const = 0;
 
-  Expected<SmallString<0>> assembleSnippet(const BenchmarkCode &BC,
-                                           const SnippetRepetitor &Repetitor,
-                                           unsigned MinInstructions,
-                                           unsigned LoopBodySize) const;
+  Expected<SmallString<0>>
+  assembleSnippet(const BenchmarkCode &BC, const SnippetRepetitor &Repetitor,
+                  unsigned MinInstructions, unsigned LoopBodySize,
+                  bool GenerateMemoryInstructions) const;
 
   Expected<std::string> writeObjectFile(StringRef Buffer,
                                         StringRef FileName) const;
 
   const std::unique_ptr<ScratchSpace> Scratch;
 
   Expected<std::unique_ptr<FunctionExecutor>>
   createFunctionExecutor(object::OwningBinary<object::ObjectFile> Obj,
                          const BenchmarkKey &Key) const;
 };
 
 } // namespace exegesis
 } // namespace llvm
 
 #endif // LLVM_TOOLS_LLVM_EXEGESIS_BENCHMARKRUNNER_H

llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

 #include <memory>
 #include <string>
 
 #include "Assembler.h"
 #include "BenchmarkRunner.h"
 #include "Error.h"
 #include "MCInstrDescView.h"
 #include "PerfHelper.h"
+#include "SubprocessMemory.h"
 #include "Target.h"
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/Signals.h"
 
 #ifdef __linux__
 #ifdef HAVE_LIBPFM
 #include <perfmon/perf_event.h>
 #endif
 #include <sys/mman.h>
 #include <sys/ptrace.h>
 #include <sys/syscall.h>
 #include <sys/wait.h>
 #include <unistd.h>
+
+#ifdef __GLIBC__
+#if __GLIBC_MINOR__ >= 35
+#define GLIBC_INITS_RSEQ
+#endif // __GLIBC__MINOR > 35
+#endif // __GLIBC__
+
+#ifdef GLIBC_INITS_RSEQ
+#include <sys/rseq.h>
+#endif // HAS_RSEQ
 #endif // __linux__
 
 namespace llvm {
 namespace exegesis {
 
 BenchmarkRunner::BenchmarkRunner(const LLVMState &State, Benchmark::ModeE Mode,
                                  BenchmarkPhaseSelectorE BenchmarkPhaseSelector,
                                  ExecutionModeE ExecutionMode)
SubProcessFunctionExecutorImpl(const LLVMState &State,
                                  object::OwningBinary<object::ObjectFile> Obj,
                                  const BenchmarkKey &Key)
       : State(State), Function(State.createTargetMachine(), std::move(Obj)),
         Key(Key) {}
 
 private:
   enum ChildProcessExitCodeE {
     CounterFDReadFailed = 1,
-    TranslatingCounterFDFailed
+    TranslatingCounterFDFailed,
+    RSeqDisableFailed,
+    FunctionDataMappingFailed,
+    AuxiliaryMemorySetupFailed
+
   };
 
   StringRef childProcessExitCodeToString(int ExitCode) const {
     switch (ExitCode) {
     case ChildProcessExitCodeE::CounterFDReadFailed:
       return "Counter file descriptor read failed";
     case ChildProcessExitCodeE::TranslatingCounterFDFailed:
       return "Translating counter file descriptor into a file descriptor in "
              "the child process failed. This might be due running an older "
              "Linux kernel that doesn't support the pidfd_getfd system call "
              "(anything before Linux 5.6).";
+             "the child process failed";
+    case ChildProcessExitCodeE::RSeqDisableFailed:
+      return "Disabling restartable sequences failed";
+    case ChildProcessExitCodeE::FunctionDataMappingFailed:
+      return "Failed to map memory for assembled snippet";
+    case ChildProcessExitCodeE::AuxiliaryMemorySetupFailed:
+      return "Failed to setup auxiliary memory";
     default:
       return "Child process returned with unknown exit code";
     }
   }
 
   Error createSubProcessAndRunBenchmark(
       StringRef CounterName, SmallVectorImpl<int64_t> &CounterValues) const {
     int PipeFiles[2];
     int PipeSuccessOrErr = pipe(PipeFiles);
     if (PipeSuccessOrErr != 0) {
       return make_error<Failure>(
           "Failed to create a pipe for interprocess communication between "
           "llvm-exegesis and the benchmarking subprocess");
     }
 
+    SubprocessMemory SPMemory;
+    Error MemoryInitError = SPMemory.initializeSubprocessMemory(getpid());
+    if (MemoryInitError)
+      return MemoryInitError;
+
+    Error AddMemDefError =
+        SPMemory.addMemoryDefinition(Key.MemoryValues, getpid());
+    if (AddMemDefError)
+      return AddMemDefError;
+
     pid_t ParentOrChildPID = fork();
     if (ParentOrChildPID == 0) {
       // We are in the child process, close the write end of the pipe
       close(PipeFiles[1]);
       // Unregister handlers, signal handling is now handled through ptrace in
       // the host process
       llvm::sys::unregisterHandlers();
       prepareAndRunBenchmark(PipeFiles[0], Key);
#else
     int CounterFileDescriptor = 0;
     exit(ChildProcessExitCodeE::TranslatingCounterFDFailed);
 #endif
 
     if (CounterFileDescriptor == -1) {
       exit(ChildProcessExitCodeE::TranslatingCounterFDFailed);
     }
 
-#ifdef HAVE_LIBPFM
-    ioctl(CounterFileDescriptor, PERF_EVENT_IOC_RESET);
-#endif
-    this->Function(nullptr);
-#ifdef HAVE_LIBPFM
-    ioctl(CounterFileDescriptor, PERF_EVENT_IOC_DISABLE);
-#endif
+// Glibc versions greater than 2.35 automatically call rseq during
+// initialization. Unmapping the region that glibc sets up for this causes
+// segfaults in the program Unregister the rseq region so that we can safely
+// unmap it later
+#ifdef GLIBC_INITS_RSEQ
+    long RseqDisableOutput =
+        syscall(SYS_rseq, (intptr_t)__builtin_thread_pointer() + __rseq_offset,
+                __rseq_size, RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
+    if (RseqDisableOutput != 0)
+      exit(ChildProcessExitCodeE::RSeqDisableFailed);
+#endif // GLIBC_INITS_RSEQ
+
+    size_t FunctionDataCopySize = this->Function.FunctionBytes.size();
+    char *FunctionDataCopy =
+        (char *)mmap(NULL, FunctionDataCopySize, PROT_READ | PROT_WRITE,
+                     MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
+    if ((intptr_t)FunctionDataCopy == -1)
+      exit(ChildProcessExitCodeE::FunctionDataMappingFailed);
+
+    memcpy(FunctionDataCopy, this->Function.FunctionBytes.data(),
+           this->Function.FunctionBytes.size());
+    mprotect(FunctionDataCopy, FunctionDataCopySize, PROT_READ | PROT_EXEC);
+
+    Expected<int> AuxMemFDOrError =
+        SubprocessMemory::setupAuxiliaryMemoryInSubprocess(
+            Key.MemoryValues, ParentPID, CounterFileDescriptor);
+    if (!AuxMemFDOrError)
+      exit(ChildProcessExitCodeE::AuxiliaryMemorySetupFailed);
+
+    ((void (*)(size_t, int))(intptr_t)FunctionDataCopy)(FunctionDataCopySize,
+                                                        *AuxMemFDOrError);
 
     exit(0);
   }
 
   Expected<llvm::SmallVector<int64_t, 4>>
   runWithCounter(StringRef CounterName) const override {
     SmallVector<int64_t, 4> Value(1, 0);
     Error PossibleBenchmarkError =
#endif // GLIBC_INITS_RSEQ
   const ExecutableFunction Function;
   const BenchmarkKey &Key;
 };
 #endif // __linux__
 } // namespace
 
 Expected<SmallString<0>> BenchmarkRunner::assembleSnippet(
     const BenchmarkCode &BC, const SnippetRepetitor &Repetitor,
-    unsigned MinInstructions, unsigned LoopBodySize) const {
+    unsigned MinInstructions, unsigned LoopBodySize,
+    bool GenerateMemoryInstructions) const {
   const std::vector<MCInst> &Instructions = BC.Key.Instructions;
   SmallString<0> Buffer;
   raw_svector_ostream OS(Buffer);
   if (Error E = assembleToStream(
           State.getExegesisTarget(), State.createTargetMachine(), BC.LiveIns,
           BC.Key.RegisterInitialValues,
-          Repetitor.Repeat(Instructions, MinInstructions, LoopBodySize), OS)) {
+          Repetitor.Repeat(Instructions, MinInstructions, LoopBodySize,
+                           GenerateMemoryInstructions),
+          OS, BC.Key, GenerateMemoryInstructions)) {
     return std::move(E);
   }
   return Buffer;
 }
 
 Expected<BenchmarkRunner::RunnableConfiguration>
 BenchmarkRunner::getRunnableConfiguration(
     const BenchmarkCode &BC, unsigned NumRepetitions, unsigned LoopBodySize,
     const SnippetRepetitor &Repetitor) const {
   RunnableConfiguration RC;
 
   Benchmark &InstrBenchmark = RC.InstrBenchmark;
   InstrBenchmark.Mode = Mode;
   InstrBenchmark.CpuName = std::string(State.getTargetMachine().getTargetCPU());
   InstrBenchmark.LLVMTriple =
       State.getTargetMachine().getTargetTriple().normalize();
   InstrBenchmark.NumRepetitions = NumRepetitions;
   InstrBenchmark.Info = BC.Info;
 
   const std::vector<MCInst> &Instructions = BC.Key.Instructions;
 
+  bool GenerateMemoryInstructions = ExecutionMode == ExecutionModeE::SubProcess;
+
   InstrBenchmark.Key = BC.Key;
 
   // Assemble at least kMinInstructionsForSnippet instructions by repeating
   // the snippet for debug/analysis. This is so that the user clearly
   // understands that the inside instructions are repeated.
   if (BenchmarkPhaseSelector > BenchmarkPhaseSelectorE::PrepareSnippet) {
     const int MinInstructionsForSnippet = 4 * Instructions.size();
     const int LoopBodySizeForSnippet = 2 * Instructions.size();
-    auto Snippet = assembleSnippet(BC, Repetitor, MinInstructionsForSnippet,
-                                   LoopBodySizeForSnippet);
+    auto Snippet =
+        assembleSnippet(BC, Repetitor, MinInstructionsForSnippet,
+                        LoopBodySizeForSnippet, GenerateMemoryInstructions);
     if (Error E = Snippet.takeError())
       return std::move(E);
     const ExecutableFunction EF(State.createTargetMachine(),
                                 getObjectFromBuffer(*Snippet));
     const auto FnBytes = EF.getFunctionBytes();
     llvm::append_range(InstrBenchmark.AssembledSnippet, FnBytes);
   }
 
   // Assemble NumRepetitions instructions repetitions of the snippet for
   // measurements.
-  if (BenchmarkPhaseSelector > BenchmarkPhaseSelectorE::PrepareAndAssembleSnippet) {
+  if (BenchmarkPhaseSelector >
+      BenchmarkPhaseSelectorE::PrepareAndAssembleSnippet) {
     auto Snippet = assembleSnippet(BC, Repetitor, InstrBenchmark.NumRepetitions,
-                                   LoopBodySize);
+                                   LoopBodySize, GenerateMemoryInstructions);
     if (Error E = Snippet.takeError())
       return std::move(E);
     RC.ObjectFile = getObjectFromBuffer(*Snippet);
   }
 
   return std::move(RC);
 }
 

llvm/tools/llvm-exegesis/lib/SnippetRepetitor.h

public:
   virtual ~SnippetRepetitor();
 
   // Returns the set of registers that are reserved by the repetitor.
   virtual BitVector getReservedRegs() const = 0;
 
   // Returns a functor that repeats `Instructions` so that the function executes
   // at least `MinInstructions` instructions.
   virtual FillFunction Repeat(ArrayRef<MCInst> Instructions,
-                              unsigned MinInstructions,
-                              unsigned LoopBodySize) const = 0;
+                              unsigned MinInstructions, unsigned LoopBodySize,
+                              bool CleanupMemory) const = 0;
 
   explicit SnippetRepetitor(const LLVMState &State) : State(State) {}
 
 protected:
   const LLVMState &State;
 };
 
 } // namespace exegesis
 } // namespace llvm
 
 #endif

llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp

 
 class DuplicateSnippetRepetitor : public SnippetRepetitor {
 public:
   using SnippetRepetitor::SnippetRepetitor;
 
   // Repeats the snippet until there are at least MinInstructions in the
   // resulting code.
   FillFunction Repeat(ArrayRef<MCInst> Instructions, unsigned MinInstructions,
-                      unsigned LoopBodySize) const override {
-    return [Instructions, MinInstructions](FunctionFiller &Filler) {
+                      unsigned LoopBodySize,
+                      bool CleanupMemory) const override {
+    return [this, Instructions, MinInstructions,
+            CleanupMemory](FunctionFiller &Filler) {
       auto Entry = Filler.getEntry();
       if (!Instructions.empty()) {
         // Add the whole snippet at least once.
         Entry.addInstructions(Instructions);
         for (unsigned I = Instructions.size(); I < MinInstructions; ++I) {
           Entry.addInstruction(Instructions[I % Instructions.size()]);
         }
       }
-      Entry.addReturn();
+      Entry.addReturn(State.getExegesisTarget(), CleanupMemory);
     };
   }
 
   BitVector getReservedRegs() const override {
     // We're using no additional registers.
     return State.getRATC().emptyRegisters();
   }
 };
 
 class LoopSnippetRepetitor : public SnippetRepetitor {
 public:
   explicit LoopSnippetRepetitor(const LLVMState &State)
       : SnippetRepetitor(State),
         LoopCounter(State.getExegesisTarget().getLoopCounterRegister(
             State.getTargetMachine().getTargetTriple())) {}
 
   // Loop over the snippet ceil(MinInstructions / Instructions.Size()) times.
   FillFunction Repeat(ArrayRef<MCInst> Instructions, unsigned MinInstructions,
-                      unsigned LoopBodySize) const override {
-    return [this, Instructions, MinInstructions,
-            LoopBodySize](FunctionFiller &Filler) {
+                      unsigned LoopBodySize,
+                      bool CleanupMemory) const override {
+    return [this, Instructions, MinInstructions, LoopBodySize,
+            CleanupMemory](FunctionFiller &Filler) {
       const auto &ET = State.getExegesisTarget();
       auto Entry = Filler.getEntry();
 
       // We can not use loop snippet repetitor for terminator instructions.
       for (const MCInst &Inst : Instructions) {
         const unsigned Opcode = Inst.getOpcode();
         const MCInstrDesc &MCID = Filler.MCII->get(Opcode);
         if (!MCID.isTerminator())
           continue;
-        Entry.addReturn();
+        Entry.addReturn(State.getExegesisTarget(), CleanupMemory);
         return;
       }
 
       auto Loop = Filler.addBasicBlock();
       auto Exit = Filler.addBasicBlock();
 
       const unsigned LoopUnrollFactor =
           LoopBodySize <= Instructions.size()
return [this, Instructions, MinInstructions, LoopBodySize,
         (void)_;
         Loop.addInstructions(Instructions);
       }
       ET.decrementLoopCounterAndJump(*Loop.MBB, *Loop.MBB,
                                      State.getInstrInfo());
 
       // Set up the exit basic block.
       Loop.MBB->addSuccessor(Exit.MBB, BranchProbability::getZero());
-      Exit.addReturn();
+      Exit.addReturn(State.getExegesisTarget(), CleanupMemory);
     };
   }
 
   BitVector getReservedRegs() const override {
     // We're using a single loop counter, but we have to reserve all aliasing
     // registers.
     return State.getRATC().getRegister(LoopCounter).aliasedBits();
   }

llvm/unittests/tools/llvm-exegesis/Common/AssemblerUtils.h

return std::unique_ptr<LLVMTargetMachine>(
         static_cast<LLVMTargetMachine *>(TM));
   }
 
   ExecutableFunction
   assembleToFunction(ArrayRef<RegisterValue> RegisterInitialValues,
                      FillFunction Fill) {
     SmallString<256> Buffer;
     raw_svector_ostream AsmStream(Buffer);
+    BenchmarkKey Key;
+    Key.RegisterInitialValues = RegisterInitialValues;
     EXPECT_FALSE(assembleToStream(*ET, createTargetMachine(), /*LiveIns=*/{},
-                                  RegisterInitialValues, Fill, AsmStream));
+                                  RegisterInitialValues, Fill, AsmStream, Key,
+                                  false));
     return ExecutableFunction(createTargetMachine(),
                               getObjectFromBuffer(AsmStream.str()));
   }
 
   const std::string TT;
   const std::string CpuName;
   const bool CanExecute;
   const ExegesisTarget *const ET;
 };
 
 } // namespace exegesis
 } // namespace llvm
 
 #endif

llvm/unittests/tools/llvm-exegesis/X86/SnippetRepetitorTest.cpp

void SetUp() override {
     MF = &createVoidVoidPtrMachineFunction("TestFn", Mod.get(), MMI.get());
   }
 
   void TestCommon(Benchmark::RepetitionModeE RepetitionMode) {
     const auto Repetitor = SnippetRepetitor::Create(RepetitionMode, State);
     const std::vector<MCInst> Instructions = {MCInstBuilder(X86::NOOP)};
     FunctionFiller Sink(*MF, {X86::EAX});
     const auto Fill =
-        Repetitor->Repeat(Instructions, kMinInstructions, kLoopBodySize);
+        Repetitor->Repeat(Instructions, kMinInstructions, kLoopBodySize, false);
     Fill(Sink);
   }
 
   static constexpr const unsigned kMinInstructions = 3;
   static constexpr const unsigned kLoopBodySize = 5;
 
   std::unique_ptr<LLVMTargetMachine> TM;
   std::unique_ptr<LLVMContext> Context;