Add r224985 back with two fixes.

One is that AArch64 has additional restrictions on when local relocations can
be used. We have to take those into consideration when deciding to put a L
symbol in the symbol table or not.

The other is that ld64 requires the relocations to cstring to use linker
visible symbols on AArch64.

Thanks to Michael Zolotukhin for testing this!

Remove doesSectionRequireSymbols.

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: 225644

1 files changed, 46 insertions, 70 deletions

diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
index 67b0c890085..7a83f4c64e6 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
@@ -10,6 +10,7 @@
 #include "MCTargetDesc/X86MCTargetDesc.h"
 #include "MCTargetDesc/X86FixupKinds.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCAsmLayout.h"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCContext.h"
@@ -47,23 +48,21 @@ class X86MachObjectWriter : public MCMachObjectTargetWriter {
                               const MCFixup &Fixup,
                               MCValue Target,
                               uint64_t &FixedValue);
-  void RecordX86_64Relocation(MachObjectWriter *Writer,
-                              const MCAssembler &Asm,
+  void RecordX86_64Relocation(MachObjectWriter *Writer, MCAssembler &Asm,
                               const MCAsmLayout &Layout,
-                              const MCFragment *Fragment,
-                              const MCFixup &Fixup,
-                              MCValue Target,
-                              uint64_t &FixedValue);
+                              const MCFragment *Fragment, const MCFixup &Fixup,
+                              MCValue Target, uint64_t &FixedValue);
+
 public:
   X86MachObjectWriter(bool Is64Bit, uint32_t CPUType,
                       uint32_t CPUSubtype)
     : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
                                /*UseAggressiveSymbolFolding=*/Is64Bit) {}
 
-  void RecordRelocation(MachObjectWriter *Writer,
-                        const MCAssembler &Asm, const MCAsmLayout &Layout,
-                        const MCFragment *Fragment, const MCFixup &Fixup,
-                        MCValue Target, uint64_t &FixedValue) override {
+  void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
+                        const MCAsmLayout &Layout, const MCFragment *Fragment,
+                        const MCFixup &Fixup, MCValue Target,
+                        uint64_t &FixedValue) override {
     if (Writer->is64Bit())
       RecordX86_64Relocation(Writer, Asm, Layout, Fragment, Fixup, Target,
                              FixedValue);
@@ -97,13 +96,10 @@ static unsigned getFixupKindLog2Size(unsigned Kind) {
   }
 }
 
-void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
-                                                 const MCAssembler &Asm,
-                                                 const MCAsmLayout &Layout,
-                                                 const MCFragment *Fragment,
-                                                 const MCFixup &Fixup,
-                                                 MCValue Target,
-                                                 uint64_t &FixedValue) {
+void X86MachObjectWriter::RecordX86_64Relocation(
+    MachObjectWriter *Writer, MCAssembler &Asm, const MCAsmLayout &Layout,
+    const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target,
+    uint64_t &FixedValue) {
   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
   unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind());
   unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
@@ -117,6 +113,7 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
   unsigned Index = 0;
   unsigned IsExtern = 0;
   unsigned Type = 0;
+  const MCSymbolData *RelSymbol = nullptr;
 
   Value = Target.getConstant();
 
@@ -132,7 +129,6 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
   if (Target.isAbsolute()) { // constant
     // SymbolNum of 0 indicates the absolute section.
     Type = MachO::X86_64_RELOC_UNSIGNED;
-    Index = 0;
 
     // FIXME: I believe this is broken, I don't think the linker can understand
     // it. I think it would require a local relocation, but I'm not sure if that
@@ -193,36 +189,30 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
     Value -= Writer->getSymbolAddress(&B_SD, Layout) -
       (!B_Base ? 0 : Writer->getSymbolAddress(B_Base, Layout));
 
-    if (A_Base) {
-      Index = A_Base->getIndex();
-      IsExtern = 1;
-    } else {
+    if (!A_Base)
       Index = A_SD.getFragment()->getParent()->getOrdinal() + 1;
-      IsExtern = 0;
-    }
     Type = MachO::X86_64_RELOC_UNSIGNED;
 
     MachO::any_relocation_info MRE;
     MRE.r_word0 = FixupOffset;
-    MRE.r_word1 = ((Index     <<  0) |
-                   (IsPCRel   << 24) |
-                   (Log2Size  << 25) |
-                   (IsExtern  << 27) |
-                   (Type      << 28));
-    Writer->addRelocation(Fragment->getParent(), MRE);
-
-    if (B_Base) {
-      Index = B_Base->getIndex();
-      IsExtern = 1;
-    } else {
+    MRE.r_word1 =
+        (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
+    Writer->addRelocation(A_Base, Fragment->getParent(), MRE);
+
+    if (B_Base)
+      RelSymbol = B_Base;
+    else
       Index = B_SD.getFragment()->getParent()->getOrdinal() + 1;
-      IsExtern = 0;
-    }
     Type = MachO::X86_64_RELOC_SUBTRACTOR;
   } else {
     const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
+    if (Symbol->isTemporary() && Value) {
+      const MCSection &Sec = Symbol->getSection();
+      if (!Asm.getContext().getAsmInfo()->isSectionAtomizableBySymbols(Sec))
+        Asm.addLocalUsedInReloc(*Symbol);
+    }
     const MCSymbolData &SD = Asm.getSymbolData(*Symbol);
-    const MCSymbolData *Base = Asm.getAtom(&SD);
+    RelSymbol = Asm.getAtom(&SD);
 
     // Relocations inside debug sections always use local relocations when
     // possible. This seems to be done because the debugger doesn't fully
@@ -232,23 +222,20 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
       const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
         Fragment->getParent()->getSection());
       if (Section.hasAttribute(MachO::S_ATTR_DEBUG))
-        Base = nullptr;
+        RelSymbol = nullptr;
     }
 
     // x86_64 almost always uses external relocations, except when there is no
     // symbol to use as a base address (a local symbol with no preceding
     // non-local symbol).
-    if (Base) {
-      Index = Base->getIndex();
-      IsExtern = 1;
-
+    if (RelSymbol) {
       // Add the local offset, if needed.
-      if (Base != &SD)
-        Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base);
+      if (RelSymbol != &SD)
+        Value +=
+            Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(RelSymbol);
     } else if (Symbol->isInSection() && !Symbol->isVariable()) {
       // The index is the section ordinal (1-based).
       Index = SD.getFragment()->getParent()->getOrdinal() + 1;
-      IsExtern = 0;
       Value += Writer->getSymbolAddress(&SD, Layout);
 
       if (IsPCRel)
@@ -347,12 +334,9 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
   MRE.r_word0 = FixupOffset;
-  MRE.r_word1 = ((Index     <<  0) |
-                 (IsPCRel   << 24) |
-                 (Log2Size  << 25) |
-                 (IsExtern  << 27) |
-                 (Type      << 28));
-  Writer->addRelocation(Fragment->getParent(), MRE);
+  MRE.r_word1 = (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
+                (IsExtern << 27) | (Type << 28);
+  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
 }
 
 bool X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
@@ -424,7 +408,7 @@ bool X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
                    (IsPCRel                   << 30) |
                    MachO::R_SCATTERED);
     MRE.r_word1 = 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
@@ -446,7 +430,7 @@ bool X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
                  (IsPCRel     << 30) |
                  MachO::R_SCATTERED);
   MRE.r_word1 = Value;
-  Writer->addRelocation(Fragment->getParent(), MRE);
+  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
   return true;
 }
 
@@ -467,7 +451,6 @@ void X86MachObjectWriter::RecordTLVPRelocation(MachObjectWriter *Writer,
 
   // Get the symbol data.
   const MCSymbolData *SD_A = &Asm.getSymbolData(Target.getSymA()->getSymbol());
-  unsigned Index = SD_A->getIndex();
 
   // We're only going to have a second symbol in pic mode and it'll be a
   // subtraction from the picbase. For 32-bit pic the addend is the difference
@@ -490,12 +473,9 @@ void X86MachObjectWriter::RecordTLVPRelocation(MachObjectWriter *Writer,
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
   MRE.r_word0 = Value;
-  MRE.r_word1 = ((Index                    <<  0) |
-                 (IsPCRel                  << 24) |
-                 (Log2Size                 << 25) |
-                 (1                        << 27) | // r_extern
-                 (MachO::GENERIC_RELOC_TLV << 28)); // r_type
-  Writer->addRelocation(Fragment->getParent(), MRE);
+  MRE.r_word1 =
+      (IsPCRel << 24) | (Log2Size << 25) | (MachO::GENERIC_RELOC_TLV << 28);
+  Writer->addRelocation(SD_A, Fragment->getParent(), MRE);
 }
 
 void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
@@ -546,8 +526,8 @@ void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
   // See <reloc.h>.
   uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
   unsigned Index = 0;
-  unsigned IsExtern = 0;
   unsigned Type = 0;
+  const MCSymbolData *RelSymbol = nullptr;
 
   if (Target.isAbsolute()) { // constant
     // SymbolNum of 0 indicates the absolute section.
@@ -568,8 +548,7 @@ void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
 
     // 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.
@@ -591,12 +570,9 @@ void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
   // struct relocation_info (8 bytes)
   MachO::any_relocation_info MRE;
   MRE.r_word0 = FixupOffset;
-  MRE.r_word1 = ((Index     <<  0) |
-                 (IsPCRel   << 24) |
-                 (Log2Size  << 25) |
-                 (IsExtern  << 27) |
-                 (Type      << 28));
-  Writer->addRelocation(Fragment->getParent(), MRE);
+  MRE.r_word1 =
+      (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
+  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
 }
 
 MCObjectWriter *llvm::createX86MachObjectWriter(raw_ostream &OS,