Revert r203962 and two revisions depending on it: r204028 and r204059.

The revision I'm reverting breaks handling of transitive aliases. This blocks us
and breaks sanitizer bootstrap:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap/builds/2651
(and checked locally by Alexey).

This revision is the result of:

  svn merge -r204059:204058 -r204028:204027 -r203962:203961 .

+ the regression test added to test/MC/ELF/alias.s

Another way to reproduce the regression with clang:
  $ cat q.c
  void a1();
  void a2() __attribute__((alias("a1")));
  void a3() __attribute__((alias("a2")));
  void a1() {}

  $ ~/work/llvm-build/bin/clang-3.5-good -c q.c && mv q.o good.o && \
      ~/work/llvm-build/bin/clang-3.5-bad -c q.c && mv q.o bad.o && \
      objdump -t good.o bad.o

    good.o:     file format elf64-x86-64

    SYMBOL TABLE:
    0000000000000000 l    df *ABS*  0000000000000000 q.c
    0000000000000000 l    d  .text  0000000000000000 .text
    0000000000000000 l    d  .data  0000000000000000 .data
    0000000000000000 l    d  .bss   0000000000000000 .bss
    0000000000000000 l    d  .comment       0000000000000000 .comment
    0000000000000000 l    d  .note.GNU-stack        0000000000000000 .note.GNU-stack
    0000000000000000 l    d  .eh_frame      0000000000000000 .eh_frame
    0000000000000000 g     F .text  0000000000000006 a1
    0000000000000000 g     F .text  0000000000000006 a2
    0000000000000000 g     F .text  0000000000000006 a3



    bad.o:     file format elf64-x86-64

    SYMBOL TABLE:
    0000000000000000 l    df *ABS*  0000000000000000 q.c
    0000000000000000 l    d  .text  0000000000000000 .text
    0000000000000000 l    d  .data  0000000000000000 .data
    0000000000000000 l    d  .bss   0000000000000000 .bss
    0000000000000000 l    d  .comment       0000000000000000 .comment
    0000000000000000 l    d  .note.GNU-stack        0000000000000000 .note.GNU-stack
    0000000000000000 l    d  .eh_frame      0000000000000000 .eh_frame
    0000000000000000 g     F .text  0000000000000006 a1
    0000000000000000 g     F .text  0000000000000006 a2
    0000000000000000 g       .text  0000000000000000 a3

llvm-svn: 204137

1 files changed, 39 insertions, 58 deletions

diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index dd06304b715..909ea800830 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -271,7 +271,6 @@ class ELFObjectWriter : public MCObjectWriter {
     /// \param RevGroupMap - Maps a signature symbol to the group section.
     /// \param NumRegularSections - Number of non-relocation sections.
     void ComputeSymbolTable(MCAssembler &Asm,
-                            const MCAsmLayout &Layout,
                             const SectionIndexMapTy &SectionIndexMap,
                             RevGroupMapTy RevGroupMap,
                             unsigned NumRegularSections);
@@ -463,47 +462,33 @@ void ELFObjectWriter::WriteSymbolEntry(MCDataFragment *SymtabF,
   }
 }
 
-uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &OrigData,
+uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
                                       const MCAsmLayout &Layout) {
-  MCSymbolData *Data = &OrigData;
-  if (Data->isCommon() && Data->isExternal())
-    return Data->getCommonAlignment();
-
-  const MCSymbol *Symbol = &Data->getSymbol();
-  const bool IsThumbFunc = OrigData.getFlags() & ELF_Other_ThumbFunc;
-
-  uint64_t Res = 0;
-  if (Symbol->isVariable()) {
-    const MCExpr *Expr = Symbol->getVariableValue();
-    MCValue Value;
-    if (!Expr->EvaluateAsRelocatable(Value, &Layout))
-      return 0;
-    if (Value.getSymB())
-      return 0;
-
-    Res = Value.getConstant();
-    if (IsThumbFunc)
-      Res |= 1;
-
-    const MCSymbolRefExpr *A = Value.getSymA();
-    if (!A)
-      return Res;
-
-    Symbol = &A->getSymbol();
-    Data = &Layout.getAssembler().getSymbolData(*Symbol);
+  if (Data.isCommon() && Data.isExternal())
+    return Data.getCommonAlignment();
+
+  const MCSymbol &Symbol = Data.getSymbol();
+
+  if (Symbol.isAbsolute() && Symbol.isVariable()) {
+    if (const MCExpr *Value = Symbol.getVariableValue()) {
+      int64_t IntValue;
+      if (Value->EvaluateAsAbsolute(IntValue, Layout))
+        return (uint64_t)IntValue;
+    }
   }
 
-  if (!Symbol->isInSection())
+  if (!Symbol.isInSection())
     return 0;
 
-  if (!Data->getFragment())
-    return 0;
 
-  Res += Layout.getSymbolOffset(Data);
-  if (IsThumbFunc || Data->getFlags() & ELF_Other_ThumbFunc)
-    Res |= 1;
+  if (Data.getFragment()) {
+    if (Data.getFlags() & ELF_Other_ThumbFunc)
+      return Layout.getSymbolOffset(&Data)+1;
+    else
+      return Layout.getSymbolOffset(&Data);
+  }
 
-  return Res;
+  return 0;
 }
 
 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
@@ -584,9 +569,8 @@ void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF,
                                   ELFSymbolData &MSD,
                                   const MCAsmLayout &Layout) {
   MCSymbolData &OrigData = *MSD.SymbolData;
-  const MCSymbol *Base = OrigData.getSymbol().getBaseSymbol(Layout);
-  const MCSymbolData &Data =
-      Base ? Layout.getAssembler().getSymbolData(*Base) : OrigData;
+  MCSymbolData &Data =
+    Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol());
 
   bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() ||
     Data.getSymbol().isVariable();
@@ -594,8 +578,6 @@ void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF,
   // Binding and Type share the same byte as upper and lower nibbles
   uint8_t Binding = MCELF::GetBinding(OrigData);
   uint8_t Type = mergeTypeForSet(MCELF::GetType(OrigData), MCELF::GetType(Data));
-  if (OrigData.getFlags() & ELF_Other_ThumbFunc)
-    Type = ELF::STT_FUNC;
   uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
 
   // Other and Visibility share the same byte with Visibility using the lower
@@ -604,7 +586,7 @@ void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF,
   uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
   Other |= Visibility;
 
-  uint64_t Value = SymbolValue(OrigData, Layout);
+  uint64_t Value = SymbolValue(Data, Layout);
   uint64_t Size = 0;
 
   assert(!(Data.isCommon() && !Data.isExternal()));
@@ -915,11 +897,10 @@ void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
   }
 }
 
-void
-ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
-                                    const SectionIndexMapTy &SectionIndexMap,
-                                    RevGroupMapTy RevGroupMap,
-                                    unsigned NumRegularSections) {
+void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,
+                                      const SectionIndexMapTy &SectionIndexMap,
+                                         RevGroupMapTy RevGroupMap,
+                                         unsigned NumRegularSections) {
   // FIXME: Is this the correct place to do this?
   // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
   if (NeedsGOT) {
@@ -967,33 +948,33 @@ ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
 
     ELFSymbolData MSD;
     MSD.SymbolData = it;
-    const MCSymbol *BaseSymbol = Symbol.getBaseSymbol(Layout);
+    const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
 
     // Undefined symbols are global, but this is the first place we
     // are able to set it.
     bool Local = isLocal(*it, isSignature, Used);
     if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) {
-      assert(BaseSymbol);
-      MCSymbolData &SD = Asm.getSymbolData(*BaseSymbol);
+      MCSymbolData &SD = Asm.getSymbolData(RefSymbol);
       MCELF::SetBinding(*it, ELF::STB_GLOBAL);
       MCELF::SetBinding(SD, ELF::STB_GLOBAL);
     }
 
-    if (!BaseSymbol) {
-      MSD.SectionIndex = ELF::SHN_ABS;
-    } else if (it->isCommon()) {
+    if (RefSymbol.isUndefined() && !Used && WeakrefUsed)
+      MCELF::SetBinding(*it, ELF::STB_WEAK);
+
+    if (it->isCommon()) {
       assert(!Local);
       MSD.SectionIndex = ELF::SHN_COMMON;
-    } else if (BaseSymbol->isUndefined()) {
+    } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) {
+      MSD.SectionIndex = ELF::SHN_ABS;
+    } else if (RefSymbol.isUndefined()) {
       if (isSignature && !Used)
         MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
       else
         MSD.SectionIndex = ELF::SHN_UNDEF;
-      if (!Used && WeakrefUsed)
-        MCELF::SetBinding(*it, ELF::STB_WEAK);
     } else {
       const MCSectionELF &Section =
-        static_cast<const MCSectionELF&>(BaseSymbol->getSection());
+        static_cast<const MCSectionELF&>(RefSymbol.getSection());
       MSD.SectionIndex = SectionIndexMap.lookup(&Section);
       if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
         NeedsSymtabShndx = true;
@@ -1579,8 +1560,8 @@ void ELFObjectWriter::WriteObject(MCAssembler &Asm,
   unsigned NumRegularSections = NumUserSections + NumIndexedSections;
 
   // Compute symbol table information.
-  ComputeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
-                     NumRegularSections);
+  ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections);
+
 
   WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);