[RuntimeDyld][Windows] Allocate space for dllimport things.

We weren't taking account of the space we require in the stubs for
things that are `dllimport`ed, and as a result we could hit the
assertion failure for running out of stub space.  Fix that.

rdar://133473673

Author: al45tair

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

@@ -690,9 +690,12 @@ unsigned RuntimeDyldImpl::computeSectionStubBufSize(const ObjectFile &Obj,
     if (!(RelSecI == Section))
       continue;
 
-    for (const RelocationRef &Reloc : SI->relocations())
+    for (const RelocationRef &Reloc : SI->relocations()) {
       if (relocationNeedsStub(Reloc))
         StubBufSize += StubSize;
+      if (relocationNeedsDLLImportStub(Reloc))
+        StubBufSize = sizeAfterAddingDLLImportStub(StubBufSize);
+    }
   }
 
   // Get section data size and alignment

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldCOFF.cpp

@@ -119,4 +119,15 @@ bool RuntimeDyldCOFF::isCompatibleFile(const object::ObjectFile &Obj) const {
   return Obj.isCOFF();
 }
 
+bool RuntimeDyldCOFF::relocationNeedsDLLImportStub(const RelocationRef &R) const {
+  object::symbol_iterator Symbol = R.getSymbol();
+  Expected<StringRef> TargetNameOrErr = Symbol->getName();
+  if (!TargetNameOrErr)
+    return false;
+
+  StringRef TargetName = *TargetNameOrErr;
+
+  return TargetName.startswith(getImportSymbolPrefix());
+}
+
 } // namespace llvm

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldCOFF.h

@@ -14,6 +14,7 @@
 #define LLVM_RUNTIME_DYLD_COFF_H
 
 #include "RuntimeDyldImpl.h"
+#include "llvm/Support/MathExtras.h"
 
 #define DEBUG_TYPE "dyld"
 
@@ -49,6 +50,12 @@ class RuntimeDyldCOFF : public RuntimeDyldImpl {
 
   static constexpr StringRef getImportSymbolPrefix() { return "__imp_"; }
 
+  bool relocationNeedsDLLImportStub(const RelocationRef &R) const;
+
+  unsigned sizeAfterAddingDLLImportStub(unsigned Size) const {
+    return alignTo(Size, PointerSize) + PointerSize;
+  }
+
 private:
   unsigned PointerSize;
   uint32_t PointerReloc;

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h

@@ -455,6 +455,16 @@ class RuntimeDyldImpl {
     return true;    // Conservative answer
   }
 
+  // Return true if the relocation R may require allocating a DLL import stub.
+  virtual bool relocationNeedsDLLImportStub(const RelocationRef &R) const {
+    return false;
+  }
+
+  // Add the size of a DLL import stub to the buffer size
+  virtual unsigned sizeAfterAddingDLLImportStub(unsigned Size) const {
+    return Size;
+  }
+
 public:
   RuntimeDyldImpl(RuntimeDyld::MemoryManager &MemMgr,
                   JITSymbolResolver &Resolver)