MC, COFF: Use relocations for function references inside the section

Referencing one symbol from another in the same section does not
generally require a relocation.  However, the MS linker has a feature
called /INCREMENTAL which enables incremental links.  It achieves this
by creating thunks to the actual function and redirecting all
relocations to point to the thunk.

This breaks down with the old scheme if you have a function which
references, say, itself.  On x86_64, we would use %rip relative
addressing to reference the start of the function from out current
position.  This would lead to miscompiles because other references might
reference the thunk instead, breaking function pointer equality.

This fixes PR21520.

llvm-svn: 221678

4 files changed, 26 insertions, 5 deletions

diff --git a/llvm/include/llvm/Object/COFF.h b/llvm/include/llvm/Object/COFF.h
index d9c0cd3870d..579cbadbc94 100644
--- a/llvm/include/llvm/Object/COFF.h
+++ b/llvm/include/llvm/Object/COFF.h
@@ -299,7 +299,9 @@ public:
 
   uint8_t getBaseType() const { return getType() & 0x0F; }
 
-  uint8_t getComplexType() const { return (getType() & 0xF0) >> 4; }
+  uint8_t getComplexType() const {
+    return (getType() & 0xF0) >> COFF::SCT_COMPLEX_TYPE_SHIFT;
+  }
 
   bool isExternal() const {
     return getStorageClass() == COFF::IMAGE_SYM_CLASS_EXTERNAL;
diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp
index e5f4565dafc..1046e047161 100644
--- a/llvm/lib/MC/WinCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp
@@ -170,6 +170,11 @@ public:
   void ExecutePostLayoutBinding(MCAssembler &Asm,
                                 const MCAsmLayout &Layout) override;
 
+  bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
+                                              const MCSymbolData &DataA,
+                                              const MCFragment &FB, bool InSet,
+                                              bool IsPCRel) const override;
+
   void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
                         const MCFragment *Fragment, const MCFixup &Fixup,
                         MCValue Target, bool &IsPCRel,
@@ -643,6 +648,19 @@ void WinCOFFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
       DefineSymbol(SD, Asm, Layout);
 }
 
+bool WinCOFFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
+    const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
+    bool InSet, bool IsPCRel) const {
+  // MS LINK expects to be able to replace all references to a function with a
+  // thunk to implement their /INCREMENTAL feature.  Make sure we don't optimize
+  // away any relocations to functions.
+  if ((((DataA.getFlags() & COFF::SF_TypeMask) >> COFF::SF_TypeShift) >>
+       COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
+    return false;
+  return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
+                                                                InSet, IsPCRel);
+}
+
 void WinCOFFObjectWriter::RecordRelocation(const MCAssembler &Asm,
                                            const MCAsmLayout &Layout,
                                            const MCFragment *Fragment,
diff --git a/llvm/lib/MC/WinCOFFStreamer.cpp b/llvm/lib/MC/WinCOFFStreamer.cpp
index 32813a1d263..6a8054d7486 100644
--- a/llvm/lib/MC/WinCOFFStreamer.cpp
+++ b/llvm/lib/MC/WinCOFFStreamer.cpp
@@ -133,7 +133,7 @@ void MCWinCOFFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
   if (!CurSymbol)
     FatalError("storage class specified outside of symbol definition");
 
-  if (StorageClass & ~0xff)
+  if (StorageClass & ~COFF::SSC_Invalid)
     FatalError(Twine("storage class value '") + itostr(StorageClass) +
                "' out of range");
 
diff --git a/llvm/test/MC/COFF/simple-fixups.s b/llvm/test/MC/COFF/simple-fixups.s
index 2a74f21f12d..cb5d7642ee6 100644
--- a/llvm/test/MC/COFF/simple-fixups.s
+++ b/llvm/test/MC/COFF/simple-fixups.s
@@ -1,5 +1,6 @@
-// The purpose of this test is to verify that we do not produce unneeded
-// relocations when symbols are in the same section and we know their offset.
+// The purpose of this test is to verify that we produce relocations for
+// 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
@@ -46,4 +47,4 @@ Ltmp0:
 	ret
 
 // CHECK:     Sections [
-// CHECK-NOT: RelocationCount: {{[^0]}}
+// CHECK: RelocationCount: 1