ARM: Darwin BL/BLX relocations to out-of-range symbols.

When a BL/BLX references a symbol in the same translation unit that is
out of range, use an external relocation. The linker will use this to
generate a branch island rather than a direct reference, allowing the
relocation to resolve correctly.

rdar://12359919

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164615 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp b/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
index 95640f7df951bfaf90ffeb40a1010a6bef614758..2154c931769a1d59ff7b332a621724d24f0371f2 100644 (file)
--- a/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
+++ b/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
@@ -41,6 +41,12 @@ class ARMMachObjectWriter : public MCMachObjectTargetWriter {
                                         const MCFixup &Fixup, MCValue Target,
                                         uint64_t &FixedValue);
 
+  bool requiresExternRelocation(MachObjectWriter *Writer,
+                                const MCAssembler &Asm,
+                                const MCFragment &Fragment,
+                                unsigned RelocType, const MCSymbolData *SD,
+                                uint64_t FixedValue);
+
 public:
   ARMMachObjectWriter(bool Is64Bit, uint32_t CPUType,
                       uint32_t CPUSubtype)
@@ -305,6 +311,46 @@ void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
   Writer->addRelocation(Fragment->getParent(), MRE);
 }
 
+bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
+                                                   const MCAssembler &Asm,
+                                                   const MCFragment &Fragment,
+                                                   unsigned RelocType,
+                                                   const MCSymbolData *SD,
+                                                   uint64_t FixedValue) {
+  // Most cases can be identified purely from the symbol.
+  if (Writer->doesSymbolRequireExternRelocation(SD))
+    return true;
+  int64_t Value = (int64_t)FixedValue;  // The displacement is signed.
+  int64_t Range;
+  switch (RelocType) {
+  default:
+    return false;
+  case macho::RIT_ARM_Branch24Bit:
+    // PC pre-adjustment of 8 for these instructions.
+    Value -= 8;
+    // ARM BL/BLX has a 25-bit offset.
+    Range = 0x1ffffff;
+    break;
+  case macho::RIT_ARM_ThumbBranch22Bit:
+    // PC pre-adjustment of 4 for these instructions.
+    Value -= 4;
+    // Thumb BL/BLX has a 24-bit offset.
+    Range = 0xffffff;
+  }
+  // BL/BLX also use external relocations when an internal relocation
+  // would result in the target being out of range. This gives the linker
+  // enough information to generate a branch island.
+  const MCSectionData &SymSD = Asm.getSectionData(
+    SD->getSymbol().getSection());
+  Value += Writer->getSectionAddress(&SymSD);
+  Value -= Writer->getSectionAddress(Fragment.getParent());
+  // If the resultant value would be out of range for an internal relocation,
+  // use an external instead.
+  if (Value > Range || Value < -(Range + 1))
+    return true;
+  return false;
+}
+
 void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
                                            const MCAssembler &Asm,
                                            const MCAsmLayout &Layout,
@@ -373,7 +419,8 @@ void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
     }
 
     // Check whether we need an external or internal relocation.
-    if (Writer->doesSymbolRequireExternRelocation(SD)) {
+    if (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, SD,
+                                 FixedValue)) {
       IsExtern = 1;
       Index = SD->getIndex();
 

diff --git a/test/MC/MachO/ARM/long-call-branch-island-relocation.s b/test/MC/MachO/ARM/long-call-branch-island-relocation.s
new file mode 100644 (file)
index 0000000..8ee7da5
--- /dev/null
+++ b/test/MC/MachO/ARM/long-call-branch-island-relocation.s
@@ -0,0 +1,43 @@
+@ RUN: llvm-mc -n -triple armv7-apple-darwin10 %s -filetype=obj -o %t.o
+@ RUN: macho-dump --dump-section-data < %t.o | FileCheck %s
+
+@ rdar://12359919
+
+       .syntax unified
+       .text
+
+       .globl  _bar
+       .align  2
+       .code   16
+       .thumb_func     _bar
+_bar:
+       push    {r7, lr}
+       mov     r7, sp
+       bl      _foo
+       pop     {r7, pc}
+
+
+_junk:
+@ Make the _foo symbol sufficiently far away to force the 'bl' relocation
+@ above to be out of range. On Darwin, the assembler deals with this by
+@ generating an external relocation so the linker can create a branch
+@ island.
+
+  .space 20000000
+
+  .section     __TEXT,initcode,regular,pure_instructions
+
+       .globl  _foo
+       .align  2
+       .code   16
+_foo:
+       push    {r7, lr}
+       mov     r7, sp
+       pop     {r7, pc}
+
+
+@ CHECK:  ('_relocations', [
+@ CHECK:    # Relocation 0
+@ CHECK:    (('word-0', 0x4),
+@ CHECK:     ('word-1', 0x6d000002)),
+@ CHECK:  ])