[MC, COFF] Support link /incremental conditionally

Today, we always take into account the possibility that object files
produced by MC may be consumed by an incremental linker.  This results
in us initialing fields which vary with time (TimeDateStamp) which harms
hermetic builds (e.g. verifying a self-host went well) and produces
sub-optimal code because we cannot assume anything about the relative
position of functions within a section (call sites can get redirected
through incremental linker thunks).

Let's provide an MCTargetOption which controls this behavior so that we
can disable this functionality if we know a-priori that the build will
not rely on /incremental.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256203 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCAssembler.h

@@ -609,6 +609,7 @@ class MCAssembler {
 
   unsigned RelaxAll : 1;
   unsigned SubsectionsViaSymbols : 1;
+  unsigned IncrementalLinkerCompatible : 1;
 
   /// ELF specific e_header flags
   // It would be good if there were an MCELFAssembler class to hold this.
@@ -750,6 +751,13 @@ class MCAssembler {
   bool getSubsectionsViaSymbols() const { return SubsectionsViaSymbols; }
   void setSubsectionsViaSymbols(bool Value) { SubsectionsViaSymbols = Value; }
 
+  bool isIncrementalLinkerCompatible() const {
+    return IncrementalLinkerCompatible;
+  }
+  void setIncrementalLinkerCompatible(bool Value) {
+    IncrementalLinkerCompatible = Value;
+  }
+
   bool getRelaxAll() const { return RelaxAll; }
   void setRelaxAll(bool Value) { RelaxAll = Value; }
 

include/llvm/MC/MCTargetOptions.h

@@ -32,6 +32,7 @@ class MCTargetOptions {
   bool MCNoWarn : 1;
   bool MCSaveTempLabels : 1;
   bool MCUseDwarfDirectory : 1;
+  bool MCIncrementalLinkerCompatible : 1;
   bool ShowMCEncoding : 1;
   bool ShowMCInst : 1;
   bool AsmVerbose : 1;
@@ -53,6 +54,7 @@ inline bool operator==(const MCTargetOptions &LHS, const MCTargetOptions &RHS) {
           ARE_EQUAL(MCNoWarn) &&
           ARE_EQUAL(MCSaveTempLabels) &&
           ARE_EQUAL(MCUseDwarfDirectory) &&
+          ARE_EQUAL(MCIncrementalLinkerCompatible) &&
           ARE_EQUAL(ShowMCEncoding) &&
           ARE_EQUAL(ShowMCInst) &&
           ARE_EQUAL(AsmVerbose) &&

include/llvm/MC/MCTargetOptionsCommandFlags.h

@@ -33,6 +33,12 @@ cl::opt<bool> RelaxAll("mc-relax-all",
                        cl::desc("When used with filetype=obj, "
                                 "relax all fixups in the emitted object file"));
 
+cl::opt<bool> IncrementalLinkerCompatible(
+    "incremental-linker-compatible",
+    cl::desc(
+        "When used with filetype=obj, "
+        "emit an object file which can be used with an incremental linker"));
+
 cl::opt<int> DwarfVersion("dwarf-version", cl::desc("Dwarf version"),
                           cl::init(0));
 
@@ -56,6 +62,7 @@ static inline MCTargetOptions InitMCTargetOptionsFromFlags() {
   Options.SanitizeAddress =
       (AsmInstrumentation == MCTargetOptions::AsmInstrumentationAddress);
   Options.MCRelaxAll = RelaxAll;
+  Options.MCIncrementalLinkerCompatible = IncrementalLinkerCompatible;
   Options.DwarfVersion = DwarfVersion;
   Options.ShowMCInst = ShowMCInst;
   Options.ABIName = ABIName;

include/llvm/Support/TargetRegistry.h

@@ -141,7 +141,8 @@ class Target {
   typedef MCStreamer *(*COFFStreamerCtorTy)(MCContext &Ctx, MCAsmBackend &TAB,
                                             raw_pwrite_stream &OS,
                                             MCCodeEmitter *Emitter,
-                                            bool RelaxAll);
+                                            bool RelaxAll,
+                                            bool IncrementalLinkerCompatible);
   typedef MCTargetStreamer *(*NullTargetStreamerCtorTy)(MCStreamer &S);
   typedef MCTargetStreamer *(*AsmTargetStreamerCtorTy)(
       MCStreamer &S, formatted_raw_ostream &OS, MCInstPrinter *InstPrint,
@@ -437,14 +438,16 @@ class Target {
                                      MCAsmBackend &TAB, raw_pwrite_stream &OS,
                                      MCCodeEmitter *Emitter,
                                      const MCSubtargetInfo &STI, bool RelaxAll,
+                                     bool IncrementalLinkerCompatible,
                                      bool DWARFMustBeAtTheEnd) const {
     MCStreamer *S;
     switch (T.getObjectFormat()) {
     default:
       llvm_unreachable("Unknown object format");
     case Triple::COFF:
       assert(T.isOSWindows() && "only Windows COFF is supported");
-      S = COFFStreamerCtorFn(Ctx, TAB, OS, Emitter, RelaxAll);
+      S = COFFStreamerCtorFn(Ctx, TAB, OS, Emitter, RelaxAll,
+                             IncrementalLinkerCompatible);
       break;
     case Triple::MachO:
       if (MachOStreamerCtorFn)

lib/CodeGen/LLVMTargetMachine.cpp

@@ -203,6 +203,7 @@ bool LLVMTargetMachine::addPassesToEmitFile(
     Triple T(getTargetTriple().str());
     AsmStreamer.reset(getTarget().createMCObjectStreamer(
         T, *Context, *MAB, Out, MCE, STI, Options.MCOptions.MCRelaxAll,
+        Options.MCOptions.MCIncrementalLinkerCompatible,
         /*DWARFMustBeAtTheEnd*/ true));
     break;
   }
@@ -255,6 +256,7 @@ bool LLVMTargetMachine::addPassesToEmitMC(PassManagerBase &PM, MCContext *&Ctx,
   const MCSubtargetInfo &STI = *getMCSubtargetInfo();
   std::unique_ptr<MCStreamer> AsmStreamer(getTarget().createMCObjectStreamer(
       T, *Ctx, *MAB, Out, MCE, STI, Options.MCOptions.MCRelaxAll,
+      Options.MCOptions.MCIncrementalLinkerCompatible,
       /*DWARFMustBeAtTheEnd*/ true));
 
   // Create the AsmPrinter, which takes ownership of AsmStreamer if successful.

lib/MC/MCAssembler.cpp

@@ -337,7 +337,7 @@ MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
                          MCCodeEmitter &Emitter_, MCObjectWriter &Writer_)
     : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
       BundleAlignSize(0), RelaxAll(false), SubsectionsViaSymbols(false),
-      ELFHeaderEFlags(0) {
+      IncrementalLinkerCompatible(false), ELFHeaderEFlags(0) {
   VersionMinInfo.Major = 0; // Major version == 0 for "none specified"
 }
 
@@ -355,6 +355,7 @@ void MCAssembler::reset() {
   BundleAlignSize = 0;
   RelaxAll = false;
   SubsectionsViaSymbols = false;
+  IncrementalLinkerCompatible = false;
   ELFHeaderEFlags = 0;
   LOHContainer.reset();
   VersionMinInfo.Major = 0;

lib/MC/MCTargetOptions.cpp

@@ -15,8 +15,9 @@ namespace llvm {
 MCTargetOptions::MCTargetOptions()
     : SanitizeAddress(false), MCRelaxAll(false), MCNoExecStack(false),
       MCFatalWarnings(false), MCNoWarn(false), MCSaveTempLabels(false),
-      MCUseDwarfDirectory(false), ShowMCEncoding(false), ShowMCInst(false),
-      AsmVerbose(false), DwarfVersion(0), ABIName() {}
+      MCUseDwarfDirectory(false), MCIncrementalLinkerCompatible(false),
+      ShowMCEncoding(false), ShowMCInst(false), AsmVerbose(false),
+      DwarfVersion(0), ABIName() {}
 
 StringRef MCTargetOptions::getABIName() const {
   return ABIName;

lib/MC/WinCOFFObjectWriter.cpp

@@ -621,7 +621,8 @@ bool WinCOFFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
   // thunk to implement their /INCREMENTAL feature.  Make sure we don't optimize
   // away any relocations to functions.
   uint16_t Type = cast<MCSymbolCOFF>(SymA).getType();
-  if ((Type >> COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
+  if (Asm.isIncrementalLinkerCompatible() &&
+      (Type >> COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
     return false;
   return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
                                                                 InSet, IsPCRel);
@@ -968,13 +969,19 @@ void WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
 
   Header.PointerToSymbolTable = offset;
 
+  // FIXME: Remove the #else branch and make the #if branch unconditional once
+  // LLVM's self host configuration is aware of /Brepro.
 #if (ENABLE_TIMESTAMPS == 1)
   // MS LINK expects to be able to use this timestamp to implement their
   // /INCREMENTAL feature.
-  std::time_t Now = time(nullptr);
-  if (Now < 0 || !isUInt<32>(Now))
-    Now = UINT32_MAX;
-  Header.TimeDateStamp = Now;
+  if (Asm.isIncrementalLinkerCompatible()) {
+    std::time_t Now = time(nullptr);
+    if (Now < 0 || !isUInt<32>(Now))
+      Now = UINT32_MAX;
+    Header.TimeDateStamp = Now;
+  } else {
+    Header.TimeDateStamp = 0;
+  }
 #else
   // We want a deterministic output. It looks like GNU as also writes 0 in here.
   Header.TimeDateStamp = 0;

lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.h

@@ -86,7 +86,8 @@ MCAsmBackend *createThumbBEAsmBackend(const Target &T,
 // object file.
 MCStreamer *createARMWinCOFFStreamer(MCContext &Context, MCAsmBackend &MAB,
                                      raw_pwrite_stream &OS,
-                                     MCCodeEmitter *Emitter, bool RelaxAll);
+                                     MCCodeEmitter *Emitter, bool RelaxAll,
+                                     bool IncrementalLinkerCompatible);
 
 /// Construct an ELF Mach-O object writer.
 MCObjectWriter *createARMELFObjectWriter(raw_pwrite_stream &OS, uint8_t OSABI,

lib/Target/ARM/MCTargetDesc/ARMWinCOFFStreamer.cpp

@@ -37,11 +37,11 @@ void ARMWinCOFFStreamer::EmitThumbFunc(MCSymbol *Symbol) {
 }
 }
 
-MCStreamer *llvm::createARMWinCOFFStreamer(MCContext &Context,
-                                           MCAsmBackend &MAB,
-                                           raw_pwrite_stream &OS,
-                                           MCCodeEmitter *Emitter,
-                                           bool RelaxAll) {
-  return new ARMWinCOFFStreamer(Context, MAB, *Emitter, OS);
+MCStreamer *llvm::createARMWinCOFFStreamer(
+    MCContext &Context, MCAsmBackend &MAB, raw_pwrite_stream &OS,
+    MCCodeEmitter *Emitter, bool RelaxAll, bool IncrementalLinkerCompatible) {
+  auto *S = new ARMWinCOFFStreamer(Context, MAB, *Emitter, OS);
+  S->getAssembler().setIncrementalLinkerCompatible(IncrementalLinkerCompatible);
+  return S;
 }
 

lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h

@@ -79,7 +79,7 @@ MCAsmBackend *createX86_64AsmBackend(const Target &T, const MCRegisterInfo &MRI,
 /// Takes ownership of \p AB and \p CE.
 MCStreamer *createX86WinCOFFStreamer(MCContext &C, MCAsmBackend &AB,
                                      raw_pwrite_stream &OS, MCCodeEmitter *CE,
-                                     bool RelaxAll);
+                                     bool RelaxAll, bool IncrementalLinkerCompatible);
 
 /// Construct an X86 Mach-O object writer.
 MCObjectWriter *createX86MachObjectWriter(raw_pwrite_stream &OS, bool Is64Bit,

lib/Target/X86/MCTargetDesc/X86WinCOFFStreamer.cpp

@@ -50,9 +50,11 @@ void X86WinCOFFStreamer::FinishImpl() {
 
 MCStreamer *llvm::createX86WinCOFFStreamer(MCContext &C, MCAsmBackend &AB,
                                            raw_pwrite_stream &OS,
-                                           MCCodeEmitter *CE, bool RelaxAll) {
+                                           MCCodeEmitter *CE, bool RelaxAll,
+                                           bool IncrementalLinkerCompatible) {
   X86WinCOFFStreamer *S = new X86WinCOFFStreamer(C, AB, CE, OS);
   S->getAssembler().setRelaxAll(RelaxAll);
+  S->getAssembler().setIncrementalLinkerCompatible(IncrementalLinkerCompatible);
   return S;
 }
 

test/MC/ARM/Windows/invalid-relocation.s

@@ -1,4 +1,4 @@
-# RUN: not llvm-mc -triple thumbv7-windows -filetype obj -o /dev/null 2>&1 %s \
+# RUN: not llvm-mc -triple thumbv7-windows -incremental-linker-compatible -filetype obj -o /dev/null 2>&1 %s \
 # RUN:     | FileCheck %s
 
 	.def invalid_relocation

test/MC/COFF/simple-fixups.s

@@ -2,8 +2,8 @@
 // references to functions.  Failing to do so might cause pointer-to-function
 // equality to fail if /INCREMENTAL links are used.
 
-// RUN: llvm-mc -filetype=obj -triple i686-pc-win32 %s | llvm-readobj -s | FileCheck %s
-// RUN: llvm-mc -filetype=obj -triple x86_64-pc-win32 %s | llvm-readobj -s | FileCheck %s
+// RUN: llvm-mc -filetype=obj -incremental-linker-compatible -triple i686-pc-win32 %s | llvm-readobj -s | FileCheck %s
+// RUN: llvm-mc -filetype=obj -incremental-linker-compatible -triple x86_64-pc-win32 %s | llvm-readobj -s | FileCheck %s
 
 	.def	 _foo;
 	.scl	2;

test/MC/COFF/timestamp.s

@@ -1,4 +1,4 @@
-// RUN: llvm-mc -filetype=obj -triple i686-pc-win32 %s -o - | llvm-readobj -h | FileCheck %s
+// RUN: llvm-mc -filetype=obj -triple i686-pc-win32 -incremental-linker-compatible %s -o - | llvm-readobj -h | FileCheck %s
 // REQUIRES: timestamps
 
 // CHECK: ImageFileHeader {

tools/dsymutil/DwarfLinker.cpp

@@ -31,6 +31,7 @@
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
+#include "llvm/MC/MCTargetOptionsCommandFlags.h"
 #include "llvm/Object/MachO.h"
 #include "llvm/Support/Dwarf.h"
 #include "llvm/Support/LEB128.h"
@@ -618,9 +619,11 @@ bool DwarfStreamer::init(Triple TheTriple, StringRef OutputFilename) {
   if (EC)
     return error(Twine(OutputFilename) + ": " + EC.message(), Context);
 
-  MS = TheTarget->createMCObjectStreamer(TheTriple, *MC, *MAB, *OutFile, MCE,
-                                         *MSTI, false,
-                                         /*DWARFMustBeAtTheEnd*/ false);
+  MCTargetOptions MCOptions = InitMCTargetOptionsFromFlags();
+  MS = TheTarget->createMCObjectStreamer(
+      TheTriple, *MC, *MAB, *OutFile, MCE, *MSTI, MCOptions.MCRelaxAll,
+      MCOptions.MCIncrementalLinkerCompatible,
+      /*DWARFMustBeAtTheEnd*/ false);
   if (!MS)
     return error("no object streamer for target " + TripleName, Context);
 

tools/llvm-dwp/llvm-dwp.cpp

@@ -10,6 +10,7 @@
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCStreamer.h"
+#include "llvm/MC/MCTargetOptionsCommandFlags.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/DataExtractor.h"
 #include "llvm/Support/FileSystem.h"
@@ -404,8 +405,10 @@ int main(int argc, char **argv) {
   if (EC)
     return error(Twine(OutputFilename) + ": " + EC.message(), Context);
 
+  MCTargetOptions MCOptions = InitMCTargetOptionsFromFlags();
   std::unique_ptr<MCStreamer> MS(TheTarget->createMCObjectStreamer(
-      TheTriple, MC, *MAB, OutFile, MCE, *MSTI, false,
+      TheTriple, MC, *MAB, OutFile, MCE, *MSTI, MCOptions.MCRelaxAll,
+      MCOptions.MCIncrementalLinkerCompatible,
       /*DWARFMustBeAtTheEnd*/ false));
   if (!MS)
     return error("no object streamer for target " + TripleName, Context);

tools/llvm-mc/llvm-mc.cpp

@@ -511,9 +511,10 @@ int main(int argc, char **argv) {
 
     MCCodeEmitter *CE = TheTarget->createMCCodeEmitter(*MCII, *MRI, Ctx);
     MCAsmBackend *MAB = TheTarget->createMCAsmBackend(*MRI, TripleName, MCPU);
-    Str.reset(TheTarget->createMCObjectStreamer(TheTriple, Ctx, *MAB, *OS, CE,
-                                                *STI, RelaxAll,
-                                                /*DWARFMustBeAtTheEnd*/ false));
+    Str.reset(TheTarget->createMCObjectStreamer(
+        TheTriple, Ctx, *MAB, *OS, CE, *STI, MCOptions.MCRelaxAll,
+        MCOptions.MCIncrementalLinkerCompatible,
+        /*DWARFMustBeAtTheEnd*/ false));
     if (NoExecStack)
       Str->InitSections(true);
   }