Produce an error on non-encodable offsets for darwin ARM scattered relocations.

[dzn]

Summary

Scattered ARM relocations for Mach-O's only have 24 bits available to encode the offset. This is not checked but just truncated and can result in corrupt binaries after linking because the relocations are applied to the wrong offset. This patch will check and error out in those situations instead of emitting a wrong relocation.

[dzn]

Not sure if this warrants the #include "llvm/Support/ScopedPrinter.h" or if a different message is preferred instead.

[dzn]

Ping

[thegameg]

Sorry for the delay. LGTM, thanks!

lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp

 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCFixup.h"
 #include "llvm/MC/MCFixupKindInfo.h"
 #include "llvm/MC/MCMachObjectWriter.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/ScopedPrinter.h"
+
 using namespace llvm;
 
 namespace {
 class ARMMachObjectWriter : public MCMachObjectTargetWriter {
   void RecordARMScatteredRelocation(MachObjectWriter *Writer,
                                     const MCAssembler &Asm,
                                     const MCAsmLayout &Layout,
                                     const MCFragment *Fragment,

 RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
                                  const MCAssembler &Asm,
                                  const MCAsmLayout &Layout,
                                  const MCFragment *Fragment,
                                  const MCFixup &Fixup,
                                  MCValue Target,
                                  uint64_t &FixedValue) {
   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
+
+  if (FixupOffset & 0xff000000) {
+    Asm.getContext().reportError(Fixup.getLoc(),
+        "can not encode offset '0x" + to_hexString(FixupOffset) +
+        "' in resulting scattered relocation.");
+    return;
+  }
+
   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
   unsigned Type = MachO::ARM_RELOC_HALF;
 
   // See <reloc.h>.
   const MCSymbol *A = &Target.getSymA()->getSymbol();
 
   if (!A->getFragment()) {
     Asm.getContext().reportError(Fixup.getLoc(),
void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
                                                     const MCAsmLayout &Layout,
                                                     const MCFragment *Fragment,
                                                     const MCFixup &Fixup,
                                                     MCValue Target,
                                                     unsigned Type,
                                                     unsigned Log2Size,
                                                     uint64_t &FixedValue) {
   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
+
+  if (FixupOffset & 0xff000000) {
+    Asm.getContext().reportError(Fixup.getLoc(),
+        "can not encode offset '0x" + to_hexString(FixupOffset) +
+        "' in resulting scattered relocation.");
+    return;
+  }
+
   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
 
   // See <reloc.h>.
   const MCSymbol *A = &Target.getSymA()->getSymbol();
 
   if (!A->getFragment()) {
     Asm.getContext().reportError(Fixup.getLoc(),
                        "symbol '" + A->getName() +

test/MC/MachO/ARM/bad-darwin-ARM-offset-scattered.s

+@ RUN: not llvm-mc -n -triple armv7-apple-darwin10 %s -filetype=obj -o - 2> %t.err > %t
+@ RUN: FileCheck --check-prefix=CHECK-ERROR < %t.err %s
+
+.text
+.space 0x1029eb8
+
+fn:
+    movw  r0, :lower16:(fn2-L1)
+    andeq r0, r0, r0
+L1:
+    andeq r0, r0, r0
+
+fn2:
+
+@ CHECK-ERROR: error: can not encode offset '0x1029EB8' in resulting scattered relocation.