[BOLT] Support -hot-text in lite mode

Summary: Update special symbol references in functions that are not emitted.

(cherry picked from FBD22120995)

bolt/src/BinaryContext.cpp

@@ -40,6 +40,8 @@ namespace opts {
 extern cl::OptionCategory BoltCategory;
 
 extern cl::opt<bool> AggregateOnly;
+extern cl::opt<bool> HotText;
+extern cl::opt<bool> HotData;
 extern cl::opt<bool> StrictMode;
 extern cl::opt<bool> UseOldText;
 extern cl::opt<unsigned> Verbosity;
@@ -279,6 +281,21 @@ BinaryContext::createBinaryContext(ObjectFile *File,
   return BC;
 }
 
+bool BinaryContext::forceSymbolRelocations(StringRef SymbolName) const {
+  if (opts::HotText && (SymbolName == "__hot_start" ||
+                        SymbolName == "__hot_end"))
+    return true;
+
+  if (opts::HotData && (SymbolName == "__hot_data_start" ||
+                        SymbolName == "__hot_data_end"))
+    return true;
+
+  if (SymbolName == "_end")
+    return true;
+
+  return false;
+}
+
 std::unique_ptr<MCObjectWriter>
 BinaryContext::createObjectWriter(raw_pwrite_stream &OS) {
   return MAB->createObjectWriter(OS);

bolt/src/BinaryContext.h

@@ -231,6 +231,10 @@ public:
     HasSymbolsWithFileName = true;
   }
 
+  /// Return true if relocations against symbol with a given name
+  /// must be created.
+  bool forceSymbolRelocations(StringRef SymbolName) const;
+
   uint64_t getNumUnusedProfiledObjects() const {
     return NumUnusedProfiledObjects;
   }

bolt/src/BinaryEmitter.cpp

@@ -36,7 +36,6 @@ extern cl::opt<JumpTableSupportLevel> JumpTables;
 extern cl::opt<bool> PreserveBlocksAlignment;
 extern cl::opt<bool> PrintCacheMetrics;
 extern cl::opt<bool> UpdateDebugSections;
-extern cl::opt<bool> UpdateEnd;
 extern cl::opt<unsigned> Verbosity;
 
 cl::opt<bool>
@@ -205,10 +204,7 @@ void BinaryEmitter::emitAll(StringRef OrgSecPrefix) {
 
   emitDataSections(OrgSecPrefix);
 
-  // Update _end if needed.
-  if (opts::UpdateEnd) {
-    Streamer.EmitLabel(BC.Ctx->getOrCreateSymbol("_end"));
-  }
+  Streamer.EmitLabel(BC.Ctx->getOrCreateSymbol("_end"));
 }
 
 void BinaryEmitter::emitFunctions() {

bolt/src/BinaryFunction.cpp

@@ -1439,6 +1439,12 @@ bool BinaryFunction::scanExternalRefs() {
 
     // Return true if we can ignore reference to the symbol.
     auto ignoreReference = [&](const MCSymbol *TargetSymbol) {
+      if (!TargetSymbol)
+        return true;
+
+      if (BC.forceSymbolRelocations(TargetSymbol->getName()))
+        return false;
+
       auto *TargetFunction = BC.getFunctionForSymbol(TargetSymbol);
       if (!TargetFunction)
         return true;

bolt/src/RewriteInstance.cpp

@@ -201,13 +201,6 @@ HotData("hot-data",
   cl::ZeroOrMore,
   cl::cat(BoltCategory));
 
-cl::opt<bool>
-UpdateEnd("update-end",
-  cl::desc("update the _end symbol to point to the end of all data sections"),
-  cl::init(true),
-  cl::ZeroOrMore,
-  cl::cat(BoltCategory));
-
 cl::opt<bool>
 KeepTmp("keep-tmp",
   cl::desc("preserve intermediate .o file"),
@@ -2013,20 +2006,7 @@ void RewriteInstance::readRelocations(const SectionRef &Section) {
       continue;
     }
 
-    auto ForceRelocation = [&](StringRef SymbolName) {
-      if (opts::HotText && (SymbolName == "__hot_start" ||
-                            SymbolName == "__hot_end"))
-        return true;
-
-      if (opts::HotData && (SymbolName == "__hot_data_start" ||
-                            SymbolName == "__hot_data_end"))
-        return true;
-
-      if (SymbolName == "_end")
-        return true;
-
-      return false;
-    }(SymbolName);
+    bool ForceRelocation = BC->forceSymbolRelocations(SymbolName);
 
     if (BC->isAArch64() && RType == ELF::R_AARCH64_ADR_GOT_PAGE)
       ForceRelocation = true;
@@ -3907,7 +3887,6 @@ void RewriteInstance::updateELFSymbolTable(
       outs() << "BOLT-INFO: setting " << Name << " to 0x"
              << Twine::utohexstr(NewSymbol.st_value) << '\n';
       ++IsUpdated;
-      return true;
     };
 
     if (opts::HotText && (*SymbolName == "__hot_start" ||
@@ -3918,11 +3897,9 @@ void RewriteInstance::updateELFSymbolTable(
                           *SymbolName == "__hot_data_end"))
       updateSymbolValue(*SymbolName, NumHotDataSymsUpdated);
 
-    if (opts::UpdateEnd && *SymbolName == "_end") {
-      NewSymbol.st_value = getNewValueForSymbol(*SymbolName);
-      NewSymbol.st_shndx = ELF::SHN_ABS;
-      outs() << "BOLT-INFO: setting " << *SymbolName << " to 0x"
-             << Twine::utohexstr(NewSymbol.st_value) << '\n';
+    if (*SymbolName == "_end") {
+      unsigned Ignored;
+      updateSymbolValue(*SymbolName, Ignored);
     }
 
     if (PatchExisting) {