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Correctly handle references to section symbols.

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When processing assembly like

.long .text

we were creating a new undefined symbol .text. GAS on the other hand would
handle that as a reference to the .text section.

This patch implements that by creating the section symbols earlier so that
they are visible during asm parsing.

The patch also updates llvm-readobj to print the symbol number in the relocation
dump so that the test can differentiate between two sections with the same name.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219829 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola 2014-10-15 18:55:30 +00:00
parent 1338612c55
commit ad04f5db82
8 changed files with 160 additions and 52 deletions
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6
include/llvm/MC/MCContext.h
View File

@ -73,6 +73,10 @@ namespace llvm {
/// Symbols - Bindings of names to symbols.
SymbolTable Symbols;
/// ELF sections can have a corresponding symbol. This maps one to the
/// other.
DenseMap<const MCSectionELF*, MCSymbol*> SectionSymbols;
/// A maping from a local label number and an instance count to a symbol.
/// For example, in the assembly
/// 1:
@ -231,6 +235,8 @@ namespace llvm {
MCSymbol *GetOrCreateSymbol(StringRef Name);
MCSymbol *GetOrCreateSymbol(const Twine &Name);
MCSymbol *getOrCreateSectionSymbol(const MCSectionELF &Section);
/// LookupSymbol - Get the symbol for \p Name, or null.
MCSymbol *LookupSymbol(StringRef Name) const;
MCSymbol *LookupSymbol(const Twine &Name) const;

74
lib/MC/ELFObjectWriter.cpp
View File

@ -81,23 +81,13 @@ public:
struct ELFRelocationEntry {
uint64_t Offset; // Where is the relocation.
bool UseSymbol; // Relocate with a symbol, not the section.
union {
const MCSymbol *Symbol; // The symbol to relocate with.
const MCSectionData *Section; // The section to relocate with.
};
const MCSymbol *Symbol; // The symbol to relocate with.
unsigned Type; // The type of the relocation.
uint64_t Addend; // The addend to use.
ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type,
uint64_t Addend)
: Offset(Offset), UseSymbol(true), Symbol(Symbol), Type(Type),
Addend(Addend) {}
ELFRelocationEntry(uint64_t Offset, const MCSectionData *Section,
unsigned Type, uint64_t Addend)
: Offset(Offset), UseSymbol(false), Section(Section), Type(Type),
Addend(Addend) {}
: Offset(Offset), Symbol(Symbol), Type(Type), Addend(Addend) {}
};
class ELFObjectWriter : public MCObjectWriter {
@ -137,6 +127,14 @@ class ELFObjectWriter : public MCObjectWriter {
// Support lexicographic sorting.
bool operator<(const ELFSymbolData &RHS) const {
unsigned LHSType = MCELF::GetType(*SymbolData);
unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
return false;
if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
return true;
if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
return SectionIndex < RHS.SectionIndex;
return Name < RHS.Name;
}
};
@ -651,22 +649,6 @@ void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
WriteSymbol(Writer, MSD, Layout);
}
// Write out a symbol table entry for each regular section.
for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e;
++i) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(i->getSection());
if (Section.getType() == ELF::SHT_RELA ||
Section.getType() == ELF::SHT_REL ||
Section.getType() == ELF::SHT_STRTAB ||
Section.getType() == ELF::SHT_SYMTAB ||
Section.getType() == ELF::SHT_SYMTAB_SHNDX)
continue;
Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT,
SectionIndexMap.lookup(&Section), false);
LastLocalSymbolIndex++;
}
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
ELFSymbolData &MSD = ExternalSymbolData[i];
MCSymbolData &Data = *MSD.SymbolData;
@ -882,8 +864,11 @@ void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
if (!RelocateWithSymbol) {
const MCSection *SecA =
(SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr;
ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend);
auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
MCSymbol *SectionSymbol =
ELFSec ? Asm.getContext().GetOrCreateSymbol(ELFSec->getSectionName())
: nullptr;
ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
Relocations[FixupSection].push_back(Rec);
return;
}
@ -1061,7 +1046,10 @@ ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
Buf += Name.substr(Pos + Skip);
Name = Buf;
}
MSD.Name = StrTabBuilder.add(Name);
// Sections have their own string table
if (MCELF::GetType(SD) != ELF::STT_SECTION)
MSD.Name = StrTabBuilder.add(Name);
if (MSD.SectionIndex == ELF::SHN_UNDEF)
UndefinedSymbolData.push_back(MSD);
@ -1079,9 +1067,11 @@ ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
for (ELFSymbolData& MSD : LocalSymbolData)
MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
for (ELFSymbolData& MSD : ExternalSymbolData)
for (ELFSymbolData &MSD : LocalSymbolData)
MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
? 0
: StrTabBuilder.getOffset(MSD.Name);
for (ELFSymbolData &MSD : ExternalSymbolData)
MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
for (ELFSymbolData& MSD : UndefinedSymbolData)
MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
@ -1097,8 +1087,6 @@ ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
LocalSymbolData[i].SymbolData->setIndex(Index++);
Index += NumRegularSections;
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
ExternalSymbolData[i].SymbolData->setIndex(Index++);
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
@ -1354,18 +1342,8 @@ void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
const ELFRelocationEntry &Entry = Relocs[e - i - 1];
unsigned Index;
if (Entry.UseSymbol) {
Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol);
} else {
const MCSectionData *Sec = Entry.Section;
if (Sec)
Index = Sec->getOrdinal() + FileSymbolData.size() +
LocalSymbolData.size() + 1;
else
Index = 0;
}
unsigned Index =
Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
if (is64Bit()) {
write(*F, Entry.Offset);

17
lib/MC/MCContext.cpp
View File

@ -113,6 +113,23 @@ MCSymbol *MCContext::GetOrCreateSymbol(StringRef Name) {
return Sym;
}
MCSymbol *MCContext::getOrCreateSectionSymbol(const MCSectionELF &Section) {
MCSymbol *&Sym = SectionSymbols[&Section];
if (Sym)
return Sym;
StringRef Name = Section.getSectionName();
StringMapEntry<bool> *NameEntry = &UsedNames.GetOrCreateValue(Name);
NameEntry->setValue(true);
Sym = new (*this) MCSymbol(NameEntry->getKey(), /*isTemporary*/ false);
StringMapEntry<MCSymbol*> &Entry = Symbols.GetOrCreateValue(Name);
if (!Entry.getValue())
Entry.setValue(Sym);
return Sym;
}
MCSymbol *MCContext::CreateSymbol(StringRef Name) {
// Determine whether this is an assembler temporary or normal label, if used.
bool isTemporary = false;

13
lib/MC/MCELFStreamer.cpp
View File

@ -92,10 +92,19 @@ void MCELFStreamer::ChangeSection(const MCSection *Section,
MCSectionData *CurSection = getCurrentSectionData();
if (CurSection && CurSection->isBundleLocked())
report_fatal_error("Unterminated .bundle_lock when changing a section");
const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
MCAssembler &Asm = getAssembler();
auto *SectionELF = static_cast<const MCSectionELF *>(Section);
const MCSymbol *Grp = SectionELF->getGroup();
if (Grp)
getAssembler().getOrCreateSymbolData(*Grp);
Asm.getOrCreateSymbolData(*Grp);
this->MCObjectStreamer::ChangeSection(Section, Subsection);
MCSymbol *SectionSymbol = getContext().getOrCreateSectionSymbol(*SectionELF);
if (SectionSymbol->isUndefined()) {
EmitLabel(SectionSymbol);
MCELF::SetType(Asm.getSymbolData(*SectionSymbol), ELF::STT_SECTION);
}
}
void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {

2
test/MC/ELF/comdat.s
View File

@ -41,7 +41,7 @@
// CHECK-NEXT: Offset: 0x54
// CHECK-NEXT: Size: 12
// CHECK-NEXT: Link: 13
// CHECK-NEXT: Info: 13
// CHECK-NEXT: Info: 10
// CHECK-NEXT: AddressAlignment: 4
// CHECK-NEXT: EntrySize: 4
// CHECK-NEXT: }

6
test/MC/ELF/section-sym-err.s Normal file
View File

@ -0,0 +1,6 @@
// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o %t.o 2>&1 | FileCheck %s
.section foo
foo:
// CHECK: error: invalid symbol redefinition

91
test/MC/ELF/section-sym.s Normal file
View File

@ -0,0 +1,91 @@
// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -s -t -r --expand-relocs | FileCheck %s
.section foo, "aG", @progbits, f1, comdat
.section foo, "G", @progbits, f2, comdat
.section bar
.long foo
// Test that the relocation points to the first section foo.
// The first seciton foo has index 6
// CHECK: Section {
// CHECK: Index: 6
// CHECK-NEXT: Name: foo (28)
// CHECK-NEXT: Type: SHT_PROGBITS (0x1)
// CHECK-NEXT: Flags [ (0x202)
// CHECK-NEXT: SHF_ALLOC (0x2)
// CHECK-NEXT: SHF_GROUP (0x200)
// CHECK-NEXT: ]
// CHECK-NEXT: Address: 0x0
// CHECK-NEXT: Offset: 0x50
// CHECK-NEXT: Size: 0
// CHECK-NEXT: Link: 0
// CHECK-NEXT: Info: 0
// CHECK-NEXT: AddressAlignment: 1
// CHECK-NEXT: EntrySize: 0
// CHECK-NEXT: }
// CHECK-NEXT: Section {
// CHECK-NEXT: Index: 7
// CHECK-NEXT: Name: foo (28)
// CHECK-NEXT: Type: SHT_PROGBITS (0x1)
// CHECK-NEXT: Flags [ (0x200)
// CHECK-NEXT: SHF_GROUP (0x200)
// CHECK-NEXT: ]
// CHECK-NEXT: Address: 0x0
// CHECK-NEXT: Offset: 0x50
// CHECK-NEXT: Size: 0
// CHECK-NEXT: Link: 0
// CHECK-NEXT: Info: 0
// CHECK-NEXT: AddressAlignment: 1
// CHECK-NEXT: EntrySize: 0
// CHECK-NEXT: }
// The relocation points to symbol 6
// CHECK: Relocations [
// CHECK-NEXT: Section (9) .relabar {
// CHECK-NEXT: Relocation {
// CHECK-NEXT: Offset: 0x0
// CHECK-NEXT: Type: R_X86_64_32 (10)
// CHECK-NEXT: Symbol: foo (6)
// CHECK-NEXT: Addend: 0x0
// CHECK-NEXT: }
// CHECK-NEXT: }
// CHECK-NEXT: ]
// The symbol 6 corresponds section 6
// CHECK: Symbols [
// symbol 0
// CHECK-NOT: Name
// CHECK: Name:
// symbol 1
// CHECK-NOT: Name
// CHECK: Name: f1
// symbol 2
// CHECK-NOT: Name
// CHECK: Name: f2
// symbol 3
// CHECK-NOT: Name
// CHECK: Name: .text
// symbol 4
// CHECK-NOT: Name
// CHECK: Name: .data
// symbol 5
// CHECK-NOT: Name
// CHECK: Name: .bss
// symbol 6
// CHECK-NOT: Name
// CHECK: Name: foo
// CHECK: Section: foo (0x6)
// symbol 7
// CHECK-NOT: Name
// CHECK: Name: foo
// CHECK: Section: foo (0x7)

3
tools/llvm-readobj/ELFDumper.cpp
View File

@ -676,7 +676,8 @@ void ELFDumper<ELFT>::printRelocation(const Elf_Shdr *Sec,
DictScope Group(W, "Relocation");
W.printHex("Offset", Rel.r_offset);
W.printNumber("Type", RelocName, (int)Rel.getType(Obj->isMips64EL()));
W.printString("Symbol", SymbolName.size() > 0 ? SymbolName : "-");
W.printNumber("Symbol", SymbolName.size() > 0 ? SymbolName : "-",
Rel.getSymbol(Obj->isMips64EL()));
W.printHex("Addend", Rel.r_addend);
} else {
raw_ostream& OS = W.startLine();