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
llvm-svn: 164615
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
index 95640f7..2154c93 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
@@ -41,6 +41,12 @@
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 @@
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 @@
}
// 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();