[MachO] Port call graph profile section and directive

[lgrey]

Summary

This ports the .cg_profile assembly directive and call graph profile section generation to MachO from COFF/ELF. Due to MachO section naming rules, the section is called __LLVM,__cg_profile rather than .llvm.call-graph-profile as in COFF/ELF. Support for llvm-readobj is included to facilitate testing.

Corresponding LLD change is D112164

[lgrey]

Ping :)

[thakis]

Nice! lgtm. One bikeshed comment about naming below (in two places, but about the same name).

I'll note: It looks like there's no attribute to tell the linker "omit this section from the final executable" – but segment name __LLVM _almost_ has this effect. The exception is that if someone were to:

• compile with -fprofile-use= (ie do a PGO build)
• pass -Wl,-bitcode_process_mode,data to ld64
• NOT pass -Wl,-dead_strip to ld64

…then they'd end up with an __LLVM,__cgprofile in their binary:

% ~/src/llvm-project/out/gn/bin/clang baz.o bar.o -O2 -isysroot $(xcrun -show-sdk-path) -Wl,-bitcode_process_mode,data -Wl,-dead_strip 
thakis@Nicos-MacBook-Pro pgotest % otool -vl a.out | grep __LLVM
thakis@Nicos-MacBook-Pro pgotest % ~/src/llvm-project/out/gn/bin/clang baz.o bar.o -O2 -isysroot -isysroot $(xcrun -show-sdk-path) -Wl,-bitcode_process_mode,data     
thakis@Nicos-MacBook-Pro pgotest % otool -vl a.out | grep -C2 __LLVM
      cmd LC_SEGMENT_64
  cmdsize 152
  segname __LLVM
   vmaddr 0x000000010000c000
   vmsize 0x0000000000004000
--
Section
  sectname __cg_profile
   segname __LLVM
      addr 0x000000010000c000
      size 0x0000000000000020

(.o files generated by adding -c to this line https://github.com/nico/hack/blob/main/pgotest/build.sh#L21)

This seems like a very unlikely sequence of events:

• -bitcode_process_mode is undocumented
• people who use flags as fancy as this likely also use -dead_strip

And there doesn't seem to be a better way to go about this – as far as I can tell, Mach-O doesn't have anything like IMAGE_SCN_LNK_REMOVE. Finally, the __cgprofile section is very small anyways (ref D112655).

llvm/lib/MC/MCMachOStreamer.cpp

539

(see below for name)

542

who owns this?

…oh, I see:
http://llvm-cs.pcc.me.uk/lib/MC/MCFragment.cpp#242

But is that owning?

http://llvm-cs.pcc.me.uk/include/llvm/MC/MCSection.h#50
http://llvm-cs.pcc.me.uk/include/llvm/ADT/ilist.h#307
http://llvm-cs.pcc.me.uk/include/llvm/ADT/ilist.h#41

Huh, subtle. Someone should probably change the API to use unique_ptrs one day. Bug I guess people familiar with these classes just know this.

llvm/lib/MC/MachObjectWriter.cpp

763

nit: Maybe call this CGProfileSection, else it looks very similar to Asm.CGProfile

(would also match COFF)

llvm/test/MC/MachO/cgprofile.s

45

nit: add newline

[lgrey]

Variable renames, added missing newline

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

if (auto *LinkerOptions = M.getNamedMetadata("llvm.linker.options")) {
     }
   }
 
   unsigned VersionVal = 0;
   unsigned ImageInfoFlags = 0;
   StringRef SectionVal;
 
   GetObjCImageInfo(M, VersionVal, ImageInfoFlags, SectionVal);
+  emitCGProfileMetadata(Streamer, M);
 
   // The section is mandatory. If we don't have it, then we don't have GC info.
   if (SectionVal.empty())
     return;
 
   StringRef Segment, Section;
   unsigned TAA = 0, StubSize = 0;
   bool TAAParsed;

llvm/lib/MC/MCMachOStreamer.cpp

public:
 
   void emitIdent(StringRef IdentString) override {
     llvm_unreachable("macho doesn't support this directive");
   }
 
   void emitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) override {
     getAssembler().getLOHContainer().addDirective(Kind, Args);
   }
+  void emitCGProfileEntry(const MCSymbolRefExpr *From,
+                          const MCSymbolRefExpr *To, uint64_t Count) override {
+    if (!From->getSymbol().isTemporary() && !To->getSymbol().isTemporary())
+      getAssembler().CGProfile.push_back({From, To, Count});
+  }
 
   void finishImpl() override;
+
+  void finalizeCGProfileEntry(const MCSymbolRefExpr *&SRE);
+  void finalizeCGProfile();
 };
 
 } // end anonymous namespace.
 
 static bool canGoAfterDWARF(const MCSectionMachO &MSec) {
   // These sections are created by the assembler itself after the end of
   // the .s file.
   StringRef SegName = MSec.getSegmentName();
static bool canGoAfterDWARF(const MCSectionMachO &MSec) {
   }
 
   if (SegName == "__TEXT" && SecName == "__eh_frame")
     return true;
 
   if (SegName == "__DATA" && (SecName == "__nl_symbol_ptr" ||
                               SecName == "__thread_ptr"))
     return true;
-
+  if (SegName == "__LLVM" && SecName == "__cg_profile")
+    return true;
   return false;
 }
 
 void MCMachOStreamer::changeSection(MCSection *Section,
                                     const MCExpr *Subsection) {
   // Change the section normally.
   bool Created = changeSectionImpl(Section, Subsection);
   const MCSectionMachO &MSec = *cast<MCSectionMachO>(Section);
for (MCSection &Sec : getAssembler()) {
     const MCSymbol *CurrentAtom = nullptr;
     for (MCFragment &Frag : Sec) {
       if (const MCSymbol *Symbol = DefiningSymbolMap.lookup(&Frag))
         CurrentAtom = Symbol;
       Frag.setAtom(CurrentAtom);
     }
   }
 
+  finalizeCGProfile();
+
   this->MCObjectStreamer::finishImpl();
 }
 
+void MCMachOStreamer::finalizeCGProfileEntry(const MCSymbolRefExpr *&SRE) {
+  const MCSymbol *S = &SRE->getSymbol();
+  bool Created;
+  getAssembler().registerSymbol(*S, &Created);
+  if (Created)
+    S->setExternal(true);
+}
+
+void MCMachOStreamer::finalizeCGProfile() {
+  MCAssembler &Asm = getAssembler();
+  if (Asm.CGProfile.empty())
+    return;
+  for (MCAssembler::CGProfileEntry &E : Asm.CGProfile) {
+    finalizeCGProfileEntry(E.From);
+    finalizeCGProfileEntry(E.To);
+  }
+  // We can't write the section out until symbol indices are finalized which
+  // doesn't happen until after section layout. We need to create the section
+  // and set its size now so that it's accounted for in layout.
+  MCSection *CGProfile = Asm.getContext().getMachOSection(
+      "__LLVM", "__cg_profile", 0, SectionKind::getMetadata());
+  Asm.registerSection(*CGProfile);
+  auto *Frag = new MCDataFragment(CGProfile);
+  // For each entry, reserve space for 2 32-bit indices and a 64-bit count.
+  size_t SectionBytes =
+      Asm.CGProfile.size() * (2 * sizeof(uint32_t) + sizeof(uint64_t));
+  Frag->getContents().resize(SectionBytes);
+}
+
 MCStreamer *llvm::createMachOStreamer(MCContext &Context,
                                       std::unique_ptr<MCAsmBackend> &&MAB,
                                       std::unique_ptr<MCObjectWriter> &&OW,
                                       std::unique_ptr<MCCodeEmitter> &&CE,
                                       bool RelaxAll, bool DWARFMustBeAtTheEnd,
                                       bool LabelSections) {
   MCMachOStreamer *S =
       new MCMachOStreamer(Context, std::move(MAB), std::move(OW), std::move(CE),
                           DWARFMustBeAtTheEnd, LabelSections);
   const Triple &Target = Context.getTargetTriple();
   S->emitVersionForTarget(Target, Context.getObjectFileInfo()->getSDKVersion());
   if (RelaxAll)
     S->getAssembler().setRelaxAll(true);
   return S;
 }

llvm/lib/MC/MCParser/DarwinAsmParser.cpp

addDirectiveHandler<&DarwinAsmParser::parseWatchOSVersionMin>(
       ".watchos_version_min");
     addDirectiveHandler<&DarwinAsmParser::parseTvOSVersionMin>(
       ".tvos_version_min");
     addDirectiveHandler<&DarwinAsmParser::parseIOSVersionMin>(
       ".ios_version_min");
     addDirectiveHandler<&DarwinAsmParser::parseMacOSXVersionMin>(
       ".macosx_version_min");
     addDirectiveHandler<&DarwinAsmParser::parseBuildVersion>(".build_version");
+    addDirectiveHandler<&DarwinAsmParser::parseDirectiveCGProfile>(
+        ".cg_profile");
 
     LastVersionDirective = SMLoc();
   }
 
   bool parseDirectiveAltEntry(StringRef, SMLoc);
   bool parseDirectiveDesc(StringRef, SMLoc);
   bool parseDirectiveIndirectSymbol(StringRef, SMLoc);
   bool parseDirectiveDumpOrLoad(StringRef, SMLoc);
public:
   bool parseMajorMinorVersionComponent(unsigned *Major, unsigned *Minor,
                                        const char *VersionName);
   bool parseOptionalTrailingVersionComponent(unsigned *Component,
                                              const char *ComponentName);
   bool parseVersion(unsigned *Major, unsigned *Minor, unsigned *Update);
   bool parseSDKVersion(VersionTuple &SDKVersion);
   void checkVersion(StringRef Directive, StringRef Arg, SMLoc Loc,
                     Triple::OSType ExpectedOS);
+  bool parseDirectiveCGProfile(StringRef Directive, SMLoc Loc);
 };
 
 } // end anonymous namespace
 
 bool DarwinAsmParser::parseSectionSwitch(StringRef Segment, StringRef Section,
                                          unsigned TAA, unsigned Align,
                                          unsigned StubSize) {
   if (getLexer().isNot(AsmToken::EndOfStatement))
bool DarwinAsmParser::parseBuildVersion(StringRef Directive, SMLoc Loc) {
 
   Triple::OSType ExpectedOS
     = getOSTypeFromPlatform((MachO::PlatformType)Platform);
   checkVersion(Directive, PlatformName, Loc, ExpectedOS);
   getStreamer().emitBuildVersion(Platform, Major, Minor, Update, SDKVersion);
   return false;
 }
 
+/// parseDirectiveCGProfile
+///   ::= .cg_profile from, to, count
+bool DarwinAsmParser::parseDirectiveCGProfile(StringRef S, SMLoc Loc) {
+  return MCAsmParserExtension::ParseDirectiveCGProfile(S, Loc);
+}
 
 namespace llvm {
 
 MCAsmParserExtension *createDarwinAsmParser() {
   return new DarwinAsmParser;
 }
 
 } // end llvm namespace

llvm/lib/MC/MachObjectWriter.cpp

 uint64_t MachObjectWriter::writeObject(MCAssembler &Asm,
                                        const MCAsmLayout &Layout) {
   uint64_t StartOffset = W.OS.tell();
 
   // Compute symbol table information and bind symbol indices.
   computeSymbolTable(Asm, LocalSymbolData, ExternalSymbolData,
                      UndefinedSymbolData);
 
+  if (!Asm.CGProfile.empty()) {
+    MCSection *CGProfile = Asm.getContext().getMachOSection(
+        "__LLVM", "__cg_profile", 0, SectionKind::getMetadata());
+    MCDataFragment *Frag = dyn_cast_or_null<MCDataFragment>(
+        &*CGProfile->getFragmentList().begin());
+    assert(Frag && "call graph profile section not reserved");
+    Frag->getContents().set_size(0);
+    raw_svector_ostream OS(Frag->getContents());
+    for (const MCAssembler::CGProfileEntry &CGPE : Asm.CGProfile) {
+      uint32_t FromIndex = CGPE.From->getSymbol().getIndex();
+      uint32_t ToIndex = CGPE.To->getSymbol().getIndex();
+      support::endian::write(OS, FromIndex, W.Endian);
+      support::endian::write(OS, ToIndex, W.Endian);
+      support::endian::write(OS, CGPE.Count, W.Endian);
+    }
+  }
+
   unsigned NumSections = Asm.size();
   const MCAssembler::VersionInfoType &VersionInfo =
     Layout.getAssembler().getVersionInfo();
 
   // The section data starts after the header, the segment load command (and
   // section headers) and the symbol table.
   unsigned NumLoadCommands = 1;
   uint64_t LoadCommandsSize = is64Bit() ?

llvm/test/MC/MachO/cgprofile.ll

+; RUN: llc -filetype=asm %s -o - -mtriple x86_64-apple-darwin | FileCheck %s
+; RUN: llc -filetype=obj %s -o %t -mtriple x86_64-apple-darwin
+; RUN: llvm-readobj --cg-profile %t | FileCheck %s --check-prefix=OBJ
+
+declare void @b()
+
+define void @a() {
+  call void @b()
+  ret void
+}
+
+define void @freq(i1 %cond) {
+  br i1 %cond, label %A, label %B
+A:
+  call void @a();
+  ret void
+B:
+  call void @b();
+  ret void
+}
+
+!llvm.module.flags = !{!0}
+
+!0 = !{i32 5, !"CG Profile", !1}
+!1 = !{!2, !3, !4, !5}
+!2 = !{void ()* @a, void ()* @b, i64 32}
+!3 = !{void (i1)* @freq, void ()* @a, i64 11}
+!4 = !{void (i1)* @freq, void ()* @b, i64 20}
+!5 = !{void (i1)* @freq, null, i64 20}
+
+; CHECK: .cg_profile _a, _b, 32
+; CHECK: .cg_profile _freq, _a, 11
+; CHECK: .cg_profile _freq, _b, 20
+
+; OBJ: CGProfile [
+; OBJ:  CGProfileEntry {
+; OBJ:    From: _a
+; OBJ:    To: _b
+; OBJ:    Weight: 32
+; OBJ:  }
+; OBJ:  CGProfileEntry {
+; OBJ:    From: _freq
+; OBJ:    To: _a
+; OBJ:    Weight: 11
+; OBJ:  }
+; OBJ:  CGProfileEntry {
+; OBJ:    From: _freq
+; OBJ:    To: _b
+; OBJ:    Weight: 20
+; OBJ:  }
+; OBJ:]

llvm/test/MC/MachO/cgprofile.s

+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t
+# RUN: llvm-readobj -S --symbols --sd --cg-profile %t | FileCheck %s
+
+  .section __TEXT,__text
+a:
+
+  .cg_profile a, b, 32
+  .cg_profile freq, a, 11
+  .cg_profile late, late2, 20
+  .cg_profile L.local, b, 42
+
+  .globl late
+late:
+late2: .word 0
+late3:
+L.local:
+
+
+# CHECK:      Name: __cg_profile
+# CHECK-NEXT: Segment: __LLVM
+# CHECK-NEXT: Address:
+# CHECK-NEXT: Size: 0x30
+# CHECK:      SectionData (
+# CHECK-NEXT:   0000: 00000000 04000000 20000000 00000000
+# CHECK-NEXT:   0010: 05000000 00000000 0B000000 00000000
+# CHECK-NEXT:   0020: 03000000 01000000 14000000 00000000
+# CHECK-NEXT: )
+
+# CHECK:        CGProfile [
+# CHECK-NEXT:   CGProfileEntry {
+# CHECK-NEXT:     From: a (0)
+# CHECK-NEXT:     To: b (4)
+# CHECK-NEXT:     Weight: 32
+# CHECK-NEXT:   }
+# CHECK-NEXT:   CGProfileEntry {
+# CHECK-NEXT:     From: freq (5)
+# CHECK-NEXT:     To: a (0)
+# CHECK-NEXT:     Weight: 11
+# CHECK-NEXT:   }
+# CHECK-NEXT:   CGProfileEntry {
+# CHECK-NEXT:     From: late (3)
+# CHECK-NEXT:     To: late2 (1)
+# CHECK-NEXT:     Weight: 20
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
 No newline at end of file

llvm/tools/llvm-readobj/MachODumper.cpp

 //===----------------------------------------------------------------------===//
 
 #include "ObjDumper.h"
 #include "StackMapPrinter.h"
 #include "llvm-readobj.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Object/MachO.h"
+#include "llvm/Support/BinaryStreamReader.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ScopedPrinter.h"
 
 using namespace llvm;
 using namespace object;
 
 namespace {
 
 class MachODumper : public ObjDumper {
 public:
   MachODumper(const MachOObjectFile *Obj, ScopedPrinter &Writer)
       : ObjDumper(Writer, Obj->getFileName()), Obj(Obj) {}
 
   void printFileHeaders() override;
   void printSectionHeaders() override;
   void printRelocations() override;
   void printUnwindInfo() override;
   void printStackMap() const override;
+  void printCGProfile() override;
 
   void printNeededLibraries() override;
 
   // MachO-specific.
   void printMachODataInCode() override;
   void printMachOVersionMin() override;
   void printMachODysymtab() override;
   void printMachOSegment() override;
   void printMachOIndirectSymbols() override;
   void printMachOLinkerOptions () override;
 
 private:
   template<class MachHeader>
   void printFileHeaders(const MachHeader &Header);
 
+  StringRef getSymbolName(const SymbolRef &Symbol);
+
   void printSymbols() override;
   void printDynamicSymbols() override;
   void printSymbol(const SymbolRef &Symbol);
 
   void printRelocation(const RelocationRef &Reloc);
 
   void printRelocation(const MachOObjectFile *Obj, const RelocationRef &Reloc);
 
void MachODumper::printRelocation(const MachOObjectFile *Obj,
   MachO::any_relocation_info RE = Obj->getRelocation(DR);
   bool IsScattered = Obj->isRelocationScattered(RE);
   bool IsExtern = !IsScattered && Obj->getPlainRelocationExternal(RE);
 
   StringRef TargetName;
   if (IsExtern) {
     symbol_iterator Symbol = Reloc.getSymbol();
     if (Symbol != Obj->symbol_end()) {
-      Expected<StringRef> TargetNameOrErr = Symbol->getName();
-      if (!TargetNameOrErr)
-        reportError(TargetNameOrErr.takeError(), Obj->getFileName());
-      TargetName = *TargetNameOrErr;
+      TargetName = getSymbolName(*Symbol);
     }
   } else if (!IsScattered) {
     section_iterator SecI = Obj->getRelocationSection(DR);
     if (SecI != Obj->section_end())
       TargetName = unwrapOrError(Obj->getFileName(), SecI->getName());
   }
   if (TargetName.empty())
     TargetName = "-";
else
       OS << " " << Obj->getPlainRelocationExternal(RE);
     OS << " " << RelocName
        << " " << IsScattered
        << " " << SymbolNameOrOffset
        << "\n";
   }
 }
 
+StringRef MachODumper::getSymbolName(const SymbolRef &Symbol) {
+  Expected<StringRef> SymbolNameOrErr = Symbol.getName();
+  if (!SymbolNameOrErr) {
+    reportError(SymbolNameOrErr.takeError(), Obj->getFileName());
+  }
+  return *SymbolNameOrErr;
+}
+
 void MachODumper::printSymbols() {
   ListScope Group(W, "Symbols");
 
   for (const SymbolRef &Symbol : Obj->symbols()) {
     printSymbol(Symbol);
   }
 }
 
 void MachODumper::printDynamicSymbols() {
   ListScope Group(W, "DynamicSymbols");
 }
 
 void MachODumper::printSymbol(const SymbolRef &Symbol) {
-  StringRef SymbolName;
-  Expected<StringRef> SymbolNameOrErr = Symbol.getName();
-  if (!SymbolNameOrErr) {
-    // TODO: Actually report errors helpfully.
-    consumeError(SymbolNameOrErr.takeError());
-  } else
-    SymbolName = *SymbolNameOrErr;
+  StringRef SymbolName = getSymbolName(Symbol);
 
   MachOSymbol MOSymbol;
   getSymbol(Obj, Symbol.getRawDataRefImpl(), MOSymbol);
 
   StringRef SectionName = "";
   // Don't ask a Mach-O STABS symbol for its section unless we know that
   // STAB symbol's section field refers to a valid section index. Otherwise
   // the symbol may error trying to load a section that does not exist.
void MachODumper::printStackMap() const {
   if (Obj->isLittleEndian())
     prettyPrintStackMap(
         W, StackMapParser<support::little>(StackMapContentsArray));
   else
     prettyPrintStackMap(
         W, StackMapParser<support::big>(StackMapContentsArray));
 }
 
+void MachODumper::printCGProfile() {
+  object::SectionRef CGProfileSection;
+  for (auto Sec : Obj->sections()) {
+    StringRef Name;
+    if (Expected<StringRef> NameOrErr = Sec.getName())
+      Name = *NameOrErr;
+    else
+      consumeError(NameOrErr.takeError());
+
+    if (Name == "__cg_profile") {
+      CGProfileSection = Sec;
+      break;
+    }
+  }
+  if (CGProfileSection == object::SectionRef())
+    return;
+
+  StringRef CGProfileContents =
+      unwrapOrError(Obj->getFileName(), CGProfileSection.getContents());
+  BinaryStreamReader Reader(CGProfileContents, Obj->isLittleEndian()
+                                                   ? llvm::support::little
+                                                   : llvm::support::big);
+
+  ListScope L(W, "CGProfile");
+  while (!Reader.empty()) {
+    uint32_t FromIndex, ToIndex;
+    uint64_t Count;
+    if (Error Err = Reader.readInteger(FromIndex))
+      reportError(std::move(Err), Obj->getFileName());
+    if (Error Err = Reader.readInteger(ToIndex))
+      reportError(std::move(Err), Obj->getFileName());
+    if (Error Err = Reader.readInteger(Count))
+      reportError(std::move(Err), Obj->getFileName());
+    DictScope D(W, "CGProfileEntry");
+    W.printNumber("From", getSymbolName(*Obj->getSymbolByIndex(FromIndex)),
+                  FromIndex);
+    W.printNumber("To", getSymbolName(*Obj->getSymbolByIndex(ToIndex)),
+                  ToIndex);
+    W.printNumber("Weight", Count);
+  }
+}
+
 void MachODumper::printNeededLibraries() {
   ListScope D(W, "NeededLibraries");
 
   using LibsTy = std::vector<StringRef>;
   LibsTy Libs;
 
   for (const auto &Command : Obj->load_commands()) {
     if (Command.C.cmd == MachO::LC_LOAD_DYLIB ||

llvm/tools/llvm-readobj/llvm-readobj.cpp

if (Obj.isMachO()) {
     if (opts::MachOLinkerOptions)
       Dumper->printMachOLinkerOptions();
     if (opts::MachOSegment)
       Dumper->printMachOSegment();
     if (opts::MachOVersionMin)
       Dumper->printMachOVersionMin();
     if (opts::MachODysymtab)
       Dumper->printMachODysymtab();
+    if (opts::CGProfile)
+      Dumper->printCGProfile();
   }
   if (opts::PrintStackMap)
     Dumper->printStackMap();
   if (opts::PrintStackSizes)
     Dumper->printStackSizes();
 }
 
 /// Dumps each object file in \a Arc;