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

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.

Patch by: Sander Bogaert (dzn)

Differential revision: https://reviews.llvm.org/D54776

llvm-svn: 347922

llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp

@@ -22,6 +22,8 @@
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/ScopedPrinter.h"
+
 using namespace llvm;
 
 namespace {
@@ -144,6 +146,15 @@ RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
                                  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;
 
@@ -250,6 +261,15 @@ void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
                                                     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>.

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

@@ -0,0 +1,15 @@
+@ 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.