Add r224985 back with fixes.

The fixes are to note that AArch64 has additional restrictions on when local
relocations can be used. In particular, ld64 requires that relocations to
cstring/cfstrings use linker visible symbols.

Original message:

In an assembly expression like

bar:
  .long L0 + 1

the intended semantics is that bar will contain a pointer one byte past L0.

In sections that are merged by content (strings, 4 byte constants, etc), a
single position in the section doesn't give the linker enough information.
For example, it would not be able to tell a relocation must point to the
end of a string, since that would look just like the start of the next.

The solution used in ELF to use relocation with symbols if there is a non-zero
addend.

In MachO before this patch we would just keep all symbols in some sections.

This would miss some cases (only cstrings on x86_64 were implemented) and was
inefficient since most relocations have an addend of 0 and can be represented
without the symbol.

This patch implements the non-zero addend logic for MachO too.

llvm-svn: 226503

1 files changed, 7 insertions, 9 deletions

diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMachObjectWriter.cpp b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMachObjectWriter.cpp
index df2f14a91a7..f7259b9a098 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMachObjectWriter.cpp
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMachObjectWriter.cpp
@@ -41,7 +41,7 @@ public:
       : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
                                  /*UseAggressiveSymbolFolding=*/Is64Bit) {}
 
-  void RecordRelocation(MachObjectWriter *Writer, const MCAssembler &Asm,
+  void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
                         const MCAsmLayout &Layout, const MCFragment *Fragment,
                         const MCFixup &Fixup, MCValue Target,
                         uint64_t &FixedValue) override {
@@ -282,7 +282,7 @@ bool PPCMachObjectWriter::RecordScatteredRelocation(
     MachO::any_relocation_info MRE;
     makeScatteredRelocationInfo(MRE, other_half, MachO::GENERIC_RELOC_PAIR,
                                 Log2Size, IsPCRel, Value2);
-    Writer->addRelocation(Fragment->getParent(), MRE);
+    Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
   } else {
     // If the offset is more than 24-bits, it won't fit in a scattered
     // relocation offset field, so we fall back to using a non-scattered
@@ -296,7 +296,7 @@ bool PPCMachObjectWriter::RecordScatteredRelocation(
   }
   MachO::any_relocation_info MRE;
   makeScatteredRelocationInfo(MRE, FixupOffset, Type, Log2Size, IsPCRel, Value);
-  Writer->addRelocation(Fragment->getParent(), MRE);
+  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
   return true;
 }
 
@@ -331,9 +331,9 @@ void PPCMachObjectWriter::RecordPPCRelocation(
   // See <reloc.h>.
   const uint32_t FixupOffset = getFixupOffset(Layout, Fragment, Fixup);
   unsigned Index = 0;
-  unsigned IsExtern = 0;
   unsigned Type = RelocType;
 
+  const MCSymbolData *RelSymbol = nullptr;
   if (Target.isAbsolute()) { // constant
                              // SymbolNum of 0 indicates the absolute section.
                              //
@@ -355,8 +355,7 @@ void PPCMachObjectWriter::RecordPPCRelocation(
 
     // Check whether we need an external or internal relocation.
     if (Writer->doesSymbolRequireExternRelocation(SD)) {
-      IsExtern = 1;
-      Index = SD->getIndex();
+      RelSymbol = SD;
       // For external relocations, make sure to offset the fixup value to
       // compensate for the addend of the symbol address, if it was
       // undefined. This occurs with weak definitions, for example.
@@ -375,9 +374,8 @@ void PPCMachObjectWriter::RecordPPCRelocation(
 
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
-  makeRelocationInfo(MRE, FixupOffset, Index, IsPCRel, Log2Size, IsExtern,
-                     Type);
-  Writer->addRelocation(Fragment->getParent(), MRE);
+  makeRelocationInfo(MRE, FixupOffset, Index, IsPCRel, Log2Size, false, Type);
+  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
 }
 
 MCObjectWriter *llvm::createPPCMachObjectWriter(raw_ostream &OS, bool Is64Bit,