[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text

Summary:
This is a re-roll of D36615 which uses PLT relocations in the back-end
to the call to __xray_CustomEvent() when building in -fPIC and
-fxray-instrument mode.

Reviewers: pcc, djasper, bkramer

Subscribers: sdardis, javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D37373

llvm-svn: 312466

1 files changed, 25 insertions, 28 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 5e002e70929..87399354945 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -2767,10 +2767,13 @@ void AsmPrinter::XRayFunctionEntry::emit(int Bytes, MCStreamer *Out,
   Out->EmitSymbolValue(Sled, Bytes);
   Out->EmitSymbolValue(CurrentFnSym, Bytes);
   auto Kind8 = static_cast<uint8_t>(Kind);
-  Out->EmitBytes(StringRef(reinterpret_cast<const char *>(&Kind8), 1));
-  Out->EmitBytes(
+  Out->EmitBinaryData(StringRef(reinterpret_cast<const char *>(&Kind8), 1));
+  Out->EmitBinaryData(
       StringRef(reinterpret_cast<const char *>(&AlwaysInstrument), 1));
-  Out->EmitZeros(2 * Bytes - 2);  // Pad the previous two entries
+  Out->EmitBinaryData(StringRef(reinterpret_cast<const char *>(&Version), 1));
+  auto Padding = (4 * Bytes) - ((2 * Bytes) + 3);
+  assert(Padding >= 0 && "Instrumentation map entry > 4 * Word Size");
+  Out->EmitZeros(Padding);
 }
 
 void AsmPrinter::emitXRayTable() {
@@ -2782,19 +2785,22 @@ void AsmPrinter::emitXRayTable() {
   MCSection *InstMap = nullptr;
   MCSection *FnSledIndex = nullptr;
   if (MF->getSubtarget().getTargetTriple().isOSBinFormatELF()) {
+    auto Associated = dyn_cast<MCSymbolELF>(PrevSection->getBeginSymbol());
+    assert(Associated != nullptr);
+    auto Flags = ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_LINK_ORDER;
+    std::string GroupName;
     if (Fn->hasComdat()) {
-      InstMap = OutContext.getELFSection("xray_instr_map", ELF::SHT_PROGBITS,
-                                         ELF::SHF_ALLOC | ELF::SHF_GROUP, 0,
-                                         Fn->getComdat()->getName());
-      FnSledIndex = OutContext.getELFSection("xray_fn_idx", ELF::SHT_PROGBITS,
-                                             ELF::SHF_ALLOC | ELF::SHF_GROUP, 0,
-                                             Fn->getComdat()->getName());
-    } else {
-      InstMap = OutContext.getELFSection("xray_instr_map", ELF::SHT_PROGBITS,
-                                         ELF::SHF_ALLOC);
-      FnSledIndex = OutContext.getELFSection("xray_fn_idx", ELF::SHT_PROGBITS,
-                                             ELF::SHF_ALLOC);
+      Flags |= ELF::SHF_GROUP;
+      GroupName = Fn->getComdat()->getName();
     }
+
+    auto UniqueID = ++XRayFnUniqueID;
+    InstMap =
+        OutContext.getELFSection("xray_instr_map", ELF::SHT_PROGBITS, Flags, 0,
+                                 GroupName, UniqueID, Associated);
+    FnSledIndex =
+        OutContext.getELFSection("xray_fn_idx", ELF::SHT_PROGBITS, Flags, 0,
+                                 GroupName, UniqueID, Associated);
   } else if (MF->getSubtarget().getTargetTriple().isOSBinFormatMachO()) {
     InstMap = OutContext.getMachOSection("__DATA", "xray_instr_map", 0,
                                          SectionKind::getReadOnlyWithRel());
@@ -2804,15 +2810,7 @@ void AsmPrinter::emitXRayTable() {
     llvm_unreachable("Unsupported target");
   }
 
-  // Before we switch over, we force a reference to a label inside the
-  // xray_fn_idx sections. This makes sure that the xray_fn_idx section is kept
-  // live by the linker if the function is not garbage-collected. Since this
-  // function is always called just before the function's end, we assume that
-  // this is happening after the last return instruction.
   auto WordSizeBytes = MAI->getCodePointerSize();
-  MCSymbol *IdxRef = OutContext.createTempSymbol("xray_fn_idx_synth_", true);
-  OutStreamer->EmitCodeAlignment(16);
-  OutStreamer->EmitSymbolValue(IdxRef, WordSizeBytes, false);
 
   // Now we switch to the instrumentation map section. Because this is done
   // per-function, we are able to create an index entry that will represent the
@@ -2831,15 +2829,14 @@ void AsmPrinter::emitXRayTable() {
   // pointers. This should work for both 32-bit and 64-bit platforms.
   OutStreamer->SwitchSection(FnSledIndex);
   OutStreamer->EmitCodeAlignment(2 * WordSizeBytes);
-  OutStreamer->EmitLabel(IdxRef);
-  OutStreamer->EmitSymbolValue(SledsStart, WordSizeBytes);
-  OutStreamer->EmitSymbolValue(SledsEnd, WordSizeBytes);
+  OutStreamer->EmitSymbolValue(SledsStart, WordSizeBytes, false);
+  OutStreamer->EmitSymbolValue(SledsEnd, WordSizeBytes, false);
   OutStreamer->SwitchSection(PrevSection);
   Sleds.clear();
 }
 
 void AsmPrinter::recordSled(MCSymbol *Sled, const MachineInstr &MI,
-  SledKind Kind) {
+                            SledKind Kind, uint8_t Version) {
   auto Fn = MI.getParent()->getParent()->getFunction();
   auto Attr = Fn->getFnAttribute("function-instrument");
   bool LogArgs = Fn->hasFnAttribute("xray-log-args");
@@ -2847,8 +2844,8 @@ void AsmPrinter::recordSled(MCSymbol *Sled, const MachineInstr &MI,
     Attr.isStringAttribute() && Attr.getValueAsString() == "xray-always";
   if (Kind == SledKind::FUNCTION_ENTER && LogArgs)
     Kind = SledKind::LOG_ARGS_ENTER;
-  Sleds.emplace_back(
-    XRayFunctionEntry{ Sled, CurrentFnSym, Kind, AlwaysInstrument, Fn });
+  Sleds.emplace_back(XRayFunctionEntry{Sled, CurrentFnSym, Kind,
+                                       AlwaysInstrument, Fn, Version});
 }
 
 uint16_t AsmPrinter::getDwarfVersion() const {