[RuntimeDyld] Skip relocations for external symbols with 64-bit address ~0ULL.

Requested by Eugene Rozenfeld of the LLILC team, this feature allows JIT
clients to skip relocations for selected external symbols by returning ~0ULL
from their symbol resolver. If this value is returned for a given symbol,
RuntimeDyld will skip all relocations for that symbol. The client will be
responsible for applying the skipped relocations manually before the code
is executed.

llvm-svn: 241383

4 files changed, 84 insertions, 21 deletions

diff --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
index 092c696d53e..6851625b9e9 100644
--- a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
+++ b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
@@ -815,12 +815,16 @@ void RuntimeDyldImpl::resolveExternalSymbols() {
         report_fatal_error("Program used external function '" + Name +
                            "' which could not be resolved!");
 
-      DEBUG(dbgs() << "Resolving relocations Name: " << Name << "\t"
-                   << format("0x%lx", Addr) << "\n");
-      // This list may have been updated when we called getSymbolAddress, so
-      // don't change this code to get the list earlier.
-      RelocationList &Relocs = i->second;
-      resolveRelocationList(Relocs, Addr);
+      // If Resolver returned UINT64_MAX, the client wants to handle this symbol
+      // manually and we shouldn't resolve its relocations.
+      if (Addr != UINT64_MAX) {
+        DEBUG(dbgs() << "Resolving relocations Name: " << Name << "\t"
+                     << format("0x%lx", Addr) << "\n");
+        // This list may have been updated when we called getSymbolAddress, so
+        // don't change this code to get the list earlier.
+        RelocationList &Relocs = i->second;
+        resolveRelocationList(Relocs, Addr);
+      }
     }
 
     ExternalSymbolRelocations.erase(i);
diff --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldChecker.cpp b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldChecker.cpp
index 957571b092d..ae199b72022 100644
--- a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldChecker.cpp
+++ b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldChecker.cpp
@@ -727,7 +727,9 @@ bool RuntimeDyldCheckerImpl::checkAllRulesInBuffer(StringRef RulePrefix,
 }
 
 bool RuntimeDyldCheckerImpl::isSymbolValid(StringRef Symbol) const {
-  return getRTDyld().getSymbolLocalAddress(Symbol) != nullptr;
+  if (getRTDyld().getSymbolLocalAddress(Symbol))
+    return true;
+  return !!getRTDyld().Resolver.findSymbol(Symbol);
 }
 
 uint64_t RuntimeDyldCheckerImpl::getSymbolLocalAddr(StringRef Symbol) const {
diff --git a/llvm/test/ExecutionEngine/RuntimeDyld/X86/MachO_x86-64_PIC_relocations.s b/llvm/test/ExecutionEngine/RuntimeDyld/X86/MachO_x86-64_PIC_relocations.s
index f28e4d24599..2ef8cc439df 100644
--- a/llvm/test/ExecutionEngine/RuntimeDyld/X86/MachO_x86-64_PIC_relocations.s
+++ b/llvm/test/ExecutionEngine/RuntimeDyld/X86/MachO_x86-64_PIC_relocations.s
@@ -1,5 +1,5 @@
 # RUN: llvm-mc -triple=x86_64-apple-macosx10.9 -relocation-model=pic -filetype=obj -o %T/test_x86-64.o %s
-# RUN: llvm-rtdyld -triple=x86_64-apple-macosx10.9 -verify -check=%s %/T/test_x86-64.o
+# RUN: llvm-rtdyld -triple=x86_64-apple-macosx10.9 -dummy-extern ds1=0xfffffffffffffffe -dummy-extern ds2=0xffffffffffffffff -verify -check=%s %/T/test_x86-64.o
 
         .section	__TEXT,__text,regular,pure_instructions
 	.globl	foo
@@ -46,4 +46,15 @@ eh_frame_test:
 x:
         .long   5
 
+# Test dummy-extern relocation.
+# rtdyld-check: *{8}z1 = ds1
+z1:
+        .quad   ds1
+
+# Test external-symbol relocation bypass: symbols with addr 0xffffffffffffffff
+# don't have their relocations applied.
+# rtdyld-check: *{8}z2 = 0
+z2:
+        .quad   ds2
+
 .subsections_via_symbols
diff --git a/llvm/tools/llvm-rtdyld/llvm-rtdyld.cpp b/llvm/tools/llvm-rtdyld/llvm-rtdyld.cpp
index 50eb87ab934..86f66f89b15 100644
--- a/llvm/tools/llvm-rtdyld/llvm-rtdyld.cpp
+++ b/llvm/tools/llvm-rtdyld/llvm-rtdyld.cpp
@@ -115,8 +115,17 @@ TargetSectionSep("target-section-sep",
 
 static cl::list<std::string>
 SpecificSectionMappings("map-section",
-                        cl::desc("Map a section to a specific address."),
-                        cl::ZeroOrMore);
+                        cl::desc("For -verify only: Map a section to a "
+                                 "specific address."),
+                        cl::ZeroOrMore,
+                        cl::Hidden);
+
+static cl::list<std::string>
+DummySymbolMappings("dummy-extern",
+                    cl::desc("For -verify only: Inject a symbol into the extern "
+                             "symbol table."),
+                    cl::ZeroOrMore,
+                    cl::Hidden);
 
 /* *** */
 
@@ -147,10 +156,25 @@ public:
   // relocations) will get to the data cache but not to the instruction cache.
   virtual void invalidateInstructionCache();
 
+  void addDummySymbol(const std::string &Name, uint64_t Addr) {
+    DummyExterns[Name] = Addr;
+  }
+
+  RuntimeDyld::SymbolInfo findSymbol(const std::string &Name) override {
+    auto I = DummyExterns.find(Name);
+
+    if (I != DummyExterns.end())
+      return RuntimeDyld::SymbolInfo(I->second, JITSymbolFlags::Exported);
+
+    return RTDyldMemoryManager::findSymbol(Name);
+  }
+
   void registerEHFrames(uint8_t *Addr, uint64_t LoadAddr,
                         size_t Size) override {}
   void deregisterEHFrames(uint8_t *Addr, uint64_t LoadAddr,
                           size_t Size) override {}
+private:
+  std::map<std::string, uint64_t> DummyExterns;
 };
 
 uint8_t *TrivialMemoryManager::allocateCodeSection(uintptr_t Size,
@@ -401,7 +425,7 @@ applySpecificSectionMappings(RuntimeDyldChecker &Checker) {
   for (StringRef Mapping : SpecificSectionMappings) {
 
     size_t EqualsIdx = Mapping.find_first_of("=");
-    StringRef SectionIDStr = Mapping.substr(0, EqualsIdx);
+    std::string SectionIDStr = Mapping.substr(0, EqualsIdx);
     size_t ComaIdx = Mapping.find_first_of(",");
 
     if (ComaIdx == StringRef::npos) {
@@ -410,8 +434,8 @@ applySpecificSectionMappings(RuntimeDyldChecker &Checker) {
       exit(1);
     }
 
-    StringRef FileName = SectionIDStr.substr(0, ComaIdx);
-    StringRef SectionName = SectionIDStr.substr(ComaIdx + 1);
+    std::string FileName = SectionIDStr.substr(0, ComaIdx);
+    std::string SectionName = SectionIDStr.substr(ComaIdx + 1);
 
     uint64_t OldAddrInt;
     std::string ErrorMsg;
@@ -425,11 +449,11 @@ applySpecificSectionMappings(RuntimeDyldChecker &Checker) {
 
     void* OldAddr = reinterpret_cast<void*>(static_cast<uintptr_t>(OldAddrInt));
 
-    StringRef NewAddrStr = Mapping.substr(EqualsIdx + 1);
+    std::string NewAddrStr = Mapping.substr(EqualsIdx + 1);
     uint64_t NewAddr;
 
-    if (NewAddrStr.getAsInteger(0, NewAddr)) {
-      errs() << "Invalid section address in mapping: " << Mapping << "\n";
+    if (StringRef(NewAddrStr).getAsInteger(0, NewAddr)) {
+      errs() << "Invalid section address in mapping '" << Mapping << "'.\n";
       exit(1);
     }
 
@@ -451,9 +475,9 @@ applySpecificSectionMappings(RuntimeDyldChecker &Checker) {
 //                            Defaults to zero. Set to something big
 //                            (e.g. 1 << 32) to stress-test stubs, GOTs, etc.
 //
-static void remapSections(const llvm::Triple &TargetTriple,
-                          const TrivialMemoryManager &MemMgr,
-                          RuntimeDyldChecker &Checker) {
+static void remapSectionsAndSymbols(const llvm::Triple &TargetTriple,
+                                    TrivialMemoryManager &MemMgr,
+                                    RuntimeDyldChecker &Checker) {
 
   // Set up a work list (section addr/size pairs).
   typedef std::list<std::pair<void*, uint64_t>> WorklistT;
@@ -516,6 +540,27 @@ static void remapSections(const llvm::Triple &TargetTriple,
     Checker.getRTDyld().mapSectionAddress(CurEntry.first, NextSectionAddr);
   }
 
+  // Add dummy symbols to the memory manager.
+  for (const auto &Mapping : DummySymbolMappings) {
+    size_t EqualsIdx = Mapping.find_first_of("=");
+
+    if (EqualsIdx == StringRef::npos) {
+      errs() << "Invalid dummy symbol specification '" << Mapping
+             << "'. Should be '<symbol name>=<addr>'\n";
+      exit(1);
+    }
+
+    std::string Symbol = Mapping.substr(0, EqualsIdx);
+    std::string AddrStr = Mapping.substr(EqualsIdx + 1);
+
+    uint64_t Addr;
+    if (StringRef(AddrStr).getAsInteger(0, Addr)) {
+      errs() << "Invalid symbol mapping '" << Mapping << "'.\n";
+      exit(1);
+    }
+
+    MemMgr.addDummySymbol(Symbol, Addr);
+  }
 }
 
 // Load and link the objects specified on the command line, but do not execute
@@ -604,8 +649,9 @@ static int linkAndVerify() {
     }
   }
 
-  // Re-map the section addresses into the phony target address space.
-  remapSections(TheTriple, MemMgr, Checker);
+  // Re-map the section addresses into the phony target address space and add
+  // dummy symbols.
+  remapSectionsAndSymbols(TheTriple, MemMgr, Checker);
 
   // Resolve all the relocations we can.
   Dyld.resolveRelocations();