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: 224985

1 files changed, 16 insertions, 21 deletions

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
index 7da500390ed..3187d36f751 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
@@ -54,10 +54,10 @@ public:
     : MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
                                /*UseAggressiveSymbolFolding=*/true) {}
 
-  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;
 };
 }
 
@@ -232,7 +232,7 @@ RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
                    (IsPCRel               << 30) |
                    MachO::R_SCATTERED);
     MRE.r_word1 = Value2;
-    Writer->addRelocation(Fragment->getParent(), MRE);
+    Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
   }
 
   MachO::any_relocation_info MRE;
@@ -243,7 +243,7 @@ RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
                  (IsPCRel     << 30) |
                  MachO::R_SCATTERED);
   MRE.r_word1 = Value;
-  Writer->addRelocation(Fragment->getParent(), MRE);
+  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
 }
 
 void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
@@ -297,7 +297,7 @@ void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
                    (IsPCRel               << 30) |
                    MachO::R_SCATTERED);
     MRE.r_word1 = Value2;
-    Writer->addRelocation(Fragment->getParent(), MRE);
+    Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
   }
 
   MachO::any_relocation_info MRE;
@@ -307,7 +307,7 @@ void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
                  (IsPCRel     << 30) |
                  MachO::R_SCATTERED);
   MRE.r_word1 = Value;
-  Writer->addRelocation(Fragment->getParent(), MRE);
+  Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
 }
 
 bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
@@ -351,11 +351,10 @@ bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
 }
 
 void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
-                                           const MCAssembler &Asm,
+                                           MCAssembler &Asm,
                                            const MCAsmLayout &Layout,
                                            const MCFragment *Fragment,
-                                           const MCFixup &Fixup,
-                                           MCValue Target,
+                                           const MCFixup &Fixup, MCValue Target,
                                            uint64_t &FixedValue) {
   unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
   unsigned Log2Size;
@@ -401,8 +400,8 @@ void ARMMachObjectWriter::RecordRelocation(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
     // FIXME!
@@ -422,8 +421,7 @@ void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
     // Check whether we need an external or internal relocation.
     if (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, SD,
                                  FixedValue)) {
-      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
@@ -447,11 +445,8 @@ void ARMMachObjectWriter::RecordRelocation(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));
+  MRE.r_word1 =
+      (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
 
   // Even when it's not a scattered relocation, movw/movt always uses
   // a PAIR relocation.
@@ -476,10 +471,10 @@ void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
                        (Log2Size              << 25) |
                        (MachO::ARM_RELOC_PAIR << 28));
 
-    Writer->addRelocation(Fragment->getParent(), MREPair);
+    Writer->addRelocation(nullptr, Fragment->getParent(), MREPair);
   }
 
-  Writer->addRelocation(Fragment->getParent(), MRE);
+  Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
 }
 
 MCObjectWriter *llvm::createARMMachObjectWriter(raw_ostream &OS,