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Handle a peculiar comdat case: Creating a section with an undefined

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signature symbol causes a local symbol to be created unless there is
some other use of the symbol.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119026 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola 2010-11-14 04:17:37 +00:00
parent 9f6e03fa1e
commit 1f4f9e3d35
3 changed files with 108 additions and 35 deletions
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76
lib/MC/ELFObjectWriter.cpp
View File

@ -285,13 +285,19 @@ namespace {
uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
const MCSymbol *S);
// Map from a group section to the signature symbol
typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
// Map from a signature symbol to the group section
typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
/// ComputeSymbolTable - Compute the symbol table data
///
/// \param StringTable [out] - The string table data.
/// \param StringIndexMap [out] - Map from symbol names to offsets in the
/// string table.
void ComputeSymbolTable(MCAssembler &Asm,
const SectionIndexMapTy &SectionIndexMap);
const SectionIndexMapTy &SectionIndexMap,
RevGroupMapTy RevGroupMap);
void ComputeIndexMap(MCAssembler &Asm,
SectionIndexMapTy &SectionIndexMap);
@ -309,10 +315,8 @@ namespace {
void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
const SectionIndexMapTy &SectionIndexMap);
// Map from a group section to the signature symbol
typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
void CreateGroupSections(MCAssembler &Asm, MCAsmLayout &Layout,
GroupMapTy &GroupMap);
GroupMapTy &GroupMap, RevGroupMapTy &RevGroupMap);
void ExecutePostLayoutBinding(MCAssembler &Asm);
@ -490,15 +494,6 @@ void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
const MCSymbol &Symbol = AliasedSymbol(Alias);
MCSymbolData &SD = Asm.getSymbolData(Symbol);
// Undefined symbols are global, but this is the first place we
// are able to set it.
if (Symbol.isUndefined() && !Symbol.isVariable()) {
if (GetBinding(SD) == ELF::STB_LOCAL) {
SetBinding(SD, ELF::STB_GLOBAL);
SetBinding(*it, ELF::STB_GLOBAL);
}
}
// Not an alias.
if (&Symbol == &Alias)
continue;
@ -904,13 +899,20 @@ static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
return true;
}
static bool isLocal(const MCSymbolData &Data) {
static bool isLocal(const MCSymbolData &Data, bool isSignature,
bool isUsedInReloc) {
if (Data.isExternal())
return false;
const MCSymbol &Symbol = Data.getSymbol();
if (Symbol.isUndefined() && !Symbol.isVariable())
const MCSymbol &RefSymbol = AliasedSymbol(Symbol);
if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) {
if (isSignature && !isUsedInReloc)
return true;
return false;
}
return true;
}
@ -938,7 +940,8 @@ void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
}
void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,
const SectionIndexMapTy &SectionIndexMap) {
const SectionIndexMapTy &SectionIndexMap,
RevGroupMapTy RevGroupMap) {
// FIXME: Is this the correct place to do this?
if (NeedsGOT) {
llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_";
@ -962,15 +965,26 @@ void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,
bool Used = UsedInReloc.count(&Symbol);
bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
if (!isInSymtab(Asm, *it, Used || WeakrefUsed,
bool isSignature = RevGroupMap.count(&Symbol);
if (!isInSymtab(Asm, *it,
Used || WeakrefUsed || isSignature,
Renames.count(&Symbol)))
continue;
ELFSymbolData MSD;
MSD.SymbolData = it;
bool Local = isLocal(*it);
const MCSymbol &RefSymbol = AliasedSymbol(Symbol);
// Undefined symbols are global, but this is the first place we
// are able to set it.
bool Local = isLocal(*it, isSignature, Used);
if (!Local && GetBinding(*it) == ELF::STB_LOCAL) {
MCSymbolData &SD = Asm.getSymbolData(RefSymbol);
SetBinding(*it, ELF::STB_GLOBAL);
SetBinding(SD, ELF::STB_GLOBAL);
}
if (RefSymbol.isUndefined() && !Used && WeakrefUsed)
SetBinding(*it, ELF::STB_WEAK);
@ -980,7 +994,10 @@ void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,
} else if (Symbol.isAbsolute() || RefSymbol.isVariable()) {
MSD.SectionIndex = ELF::SHN_ABS;
} else if (RefSymbol.isUndefined()) {
MSD.SectionIndex = ELF::SHN_UNDEF;
if (isSignature && !Used)
MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
else
MSD.SectionIndex = ELF::SHN_UNDEF;
} else {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(RefSymbol.getSection());
@ -1252,10 +1269,9 @@ bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
void ELFObjectWriter::CreateGroupSections(MCAssembler &Asm,
MCAsmLayout &Layout,
GroupMapTy &GroupMap) {
typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
GroupMapTy &GroupMap,
RevGroupMapTy &RevGroupMap) {
// Build the groups
RevGroupMapTy Groups;
for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
it != ie; ++it) {
const MCSectionELF &Section =
@ -1265,7 +1281,7 @@ void ELFObjectWriter::CreateGroupSections(MCAssembler &Asm,
const MCSymbol *SignatureSymbol = Section.getGroup();
Asm.getOrCreateSymbolData(*SignatureSymbol);
const MCSectionELF *&Group = Groups[SignatureSymbol];
const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
if (!Group) {
Group = Asm.getContext().CreateELFGroupSection();
MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
@ -1278,22 +1294,22 @@ void ELFObjectWriter::CreateGroupSections(MCAssembler &Asm,
// Add sections to the groups
unsigned Index = 1;
unsigned NumGroups = Groups.size();
unsigned NumGroups = RevGroupMap.size();
for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
it != ie; ++it, ++Index) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(it->getSection());
if (!(Section.getFlags() & MCSectionELF::SHF_GROUP))
continue;
const MCSectionELF *Group = Groups[Section.getGroup()];
const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
// FIXME: we could use the previous fragment
MCDataFragment *F = new MCDataFragment(&Data);
String32(*F, NumGroups + Index);
}
for (RevGroupMapTy::const_iterator i = Groups.begin(), e = Groups.end();
i != e; ++i) {
for (RevGroupMapTy::const_iterator i = RevGroupMap.begin(),
e = RevGroupMap.end(); i != e; ++i) {
const MCSectionELF *Group = i->second;
MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
Asm.AddSectionToTheEnd(*this, Data, Layout);
@ -1373,14 +1389,16 @@ void ELFObjectWriter::WriteSection(MCAssembler &Asm,
void ELFObjectWriter::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
GroupMapTy GroupMap;
CreateGroupSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap);
RevGroupMapTy RevGroupMap;
CreateGroupSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
RevGroupMap);
SectionIndexMapTy SectionIndexMap;
ComputeIndexMap(Asm, SectionIndexMap);
// Compute symbol table information.
ComputeSymbolTable(Asm, SectionIndexMap);
ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap);
CreateMetadataSections(const_cast<MCAssembler&>(Asm),
const_cast<MCAsmLayout&>(Layout),

8
lib/MC/MCELFStreamer.cpp
View File

@ -84,6 +84,7 @@ public:
virtual void EmitThumbFunc(MCSymbol *Func);
virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
virtual void SwitchSection(const MCSection *Section);
virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
assert(0 && "ELF doesn't support this directive");
@ -282,6 +283,13 @@ public:
};
} // end anonymous namespace
void MCELFStreamer::SwitchSection(const MCSection *Section) {
const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
if (Grp)
getAssembler().getOrCreateSymbolData(*Grp);
this->MCObjectStreamer::SwitchSection(Section);
}
void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
getAssembler().getOrCreateSymbolData(*Symbol);
MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);

59
test/MC/ELF/comdat.s
View File

@ -1,31 +1,76 @@
// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | elf-dump | FileCheck %s
// Test that we produce the two group sections and that they are a the beginning
// Test that we produce the group sections and that they are a the beginning
// of the file.
// CHECK: # Section 0x00000001
// CHECK-NEXT: (('sh_name', 0x00000021) # '.group'
// CHECK-NEXT: (('sh_name', 0x00000026) # '.group'
// CHECK-NEXT: ('sh_type', 0x00000011)
// CHECK-NEXT: ('sh_flags', 0x00000000)
// CHECK-NEXT: ('sh_addr', 0x00000000)
// CHECK-NEXT: ('sh_offset', 0x00000040)
// CHECK-NEXT: ('sh_size', 0x0000000c)
// CHECK-NEXT: ('sh_link', 0x0000000a)
// CHECK-NEXT: ('sh_link', 0x0000000c)
// CHECK-NEXT: ('sh_info', 0x00000001)
// CHECK-NEXT: ('sh_addralign', 0x00000004)
// CHECK-NEXT: ('sh_entsize', 0x00000004)
// CHECK-NEXT: ),
// CHECK-NEXT: # Section 0x00000002
// CHECK-NEXT: (('sh_name', 0x00000021) # '.group'
// CHECK-NEXT: (('sh_name', 0x00000026) # '.group'
// CHECK-NEXT: ('sh_type', 0x00000011)
// CHECK-NEXT: ('sh_flags', 0x00000000)
// CHECK-NEXT: ('sh_addr', 0x00000000)
// CHECK-NEXT: ('sh_offset', 0x0000004c)
// CHECK-NEXT: ('sh_size', 0x00000008)
// CHECK-NEXT: ('sh_link', 0x0000000a)
// CHECK-NEXT: ('sh_link', 0x0000000c)
// CHECK-NEXT: ('sh_info', 0x00000002)
// CHECK-NEXT: ('sh_addralign', 0x00000004)
// CHECK-NEXT: ('sh_entsize', 0x00000004)
// CHECK-NEXT: ),
// CHECK-NEXT: # Section 0x00000003
// CHECK-NEXT: (('sh_name', 0x00000026) # '.group'
// CHECK-NEXT: ('sh_type', 0x00000011)
// CHECK-NEXT: ('sh_flags', 0x00000000)
// CHECK-NEXT: ('sh_addr', 0x00000000)
// CHECK-NEXT: ('sh_offset', 0x00000054)
// CHECK-NEXT: ('sh_size', 0x00000008)
// CHECK-NEXT: ('sh_link', 0x0000000c)
// CHECK-NEXT: ('sh_info', 0x0000000d)
// CHECK-NEXT: ('sh_addralign', 0x00000004)
// CHECK-NEXT: ('sh_entsize', 0x00000004)
// CHECK-NEXT: ),
// Test that g1 and g2 are local, but g3 is an undefined global.
// CHECK: # Symbol 0x00000001
// CHECK-NEXT: (('st_name', 0x00000001) # 'g1'
// CHECK-NEXT: ('st_bind', 0x00000000)
// CHECK-NEXT: ('st_type', 0x00000000)
// CHECK-NEXT: ('st_other', 0x00000000)
// CHECK-NEXT: ('st_shndx', 0x00000007)
// CHECK-NEXT: ('st_value', 0x00000000)
// CHECK-NEXT: ('st_size', 0x00000000)
// CHECK-NEXT: ),
// CHECK-NEXT: # Symbol 0x00000002
// CHECK-NEXT: (('st_name', 0x00000004) # 'g2'
// CHECK-NEXT: ('st_bind', 0x00000000)
// CHECK-NEXT: ('st_type', 0x00000000)
// CHECK-NEXT: ('st_other', 0x00000000)
// CHECK-NEXT: ('st_shndx', 0x00000002)
// CHECK-NEXT: ('st_value', 0x00000000)
// CHECK-NEXT: ('st_size', 0x00000000)
// CHECK-NEXT: ),
// CHECK: # Symbol 0x0000000d
// CHECK-NEXT: (('st_name', 0x00000007) # 'g3'
// CHECK-NEXT: ('st_bind', 0x00000001)
// CHECK-NEXT: ('st_type', 0x00000000)
// CHECK-NEXT: ('st_other', 0x00000000)
// CHECK-NEXT: ('st_shndx', 0x00000000)
// CHECK-NEXT: ('st_value', 0x00000000)
// CHECK-NEXT: ('st_size', 0x00000000)
// CHECK-NEXT: ),
.section .foo,"axG",@progbits,g1,comdat
g1:
@ -35,5 +80,7 @@ g1:
nop
.section .zed,"axG",@progbits,g2,comdat
g2:
nop
.section .baz,"axG",@progbits,g3,comdat
.long g3