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[ELF] Symbol assignment within output section description 

llvm-svn: 278322
This commit is contained in:
Eugene Leviant 2016-08-11 07:56:43 +00:00
parent 88f0c31f13
commit ceabe80e97
8 changed files with 256 additions and 95 deletions
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3
lld/ELF/InputSection.cpp
View File

@ -71,6 +71,7 @@ template <class ELFT>
typename ELFT::uint InputSectionBase<ELFT>::getOffset(uintX_t Offset) const {
switch (SectionKind) {
case Regular:
case Layout:
return cast<InputSection<ELFT>>(this)->OutSecOff + Offset;
case EHFrame:
// The file crtbeginT.o has relocations pointing to the start of an empty
@ -129,7 +130,7 @@ InputSection<ELFT>::InputSection(elf::ObjectFile<ELFT> *F,
template <class ELFT>
bool InputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == Base::Regular;
return S->SectionKind == Base::Regular || S->SectionKind == Base::Layout;
}
template <class ELFT>

2
lld/ELF/InputSection.h
View File

@ -48,7 +48,7 @@ protected:
SmallVector<char, 0> Uncompressed;
public:
enum Kind { Regular, EHFrame, Merge, MipsReginfo, MipsOptions };
enum Kind { Regular, EHFrame, Merge, MipsReginfo, MipsOptions, Layout };
Kind SectionKind;
InputSectionBase() : Repl(this) {}

267
lld/ELF/LinkerScript.cpp
View File

@ -43,6 +43,36 @@ using namespace lld::elf;
ScriptConfiguration *elf::ScriptConfig;
template <class ELFT>
static Symbol *addSymbolToSymtabAux(StringRef Name, uint8_t StOther) {
return Symtab<ELFT>::X->addRegular(Name, STB_GLOBAL, StOther);
}
template <class ELFT>
static Symbol *addSymbolToSymtabAux(StringRef Name, typename ELFT::uint Value,
OutputSectionBase<ELFT> *Section) {
return Symtab<ELFT>::X->addSynthetic(Name, Section, Value);
}
template <class ELFT, class... ArgsT>
static bool addSymbolToSymtab(SymbolAssignment &Cmd, ArgsT... Args) {
if (Cmd.Name == ".")
return false;
// If a symbol was in PROVIDE(), define it only when it is an
// undefined symbol.
SymbolBody *B = Symtab<ELFT>::X->find(Cmd.Name);
if (Cmd.Provide && !(B && B->isUndefined()))
return false;
Symbol *Sym =
addSymbolToSymtabAux<ELFT>(Cmd.Name, std::forward<ArgsT>(Args)...);
Sym->Visibility = Cmd.Hidden ? STV_HIDDEN : STV_DEFAULT;
Cmd.Sym = Sym->body();
return true;
}
bool SymbolAssignment::classof(const BaseCommand *C) {
return C->Kind == AssignmentKind;
}
@ -78,21 +108,6 @@ static bool match(ArrayRef<StringRef> Patterns, StringRef S) {
return false;
}
// Create a vector of (<output section name>, <input section description>).
template <class ELFT>
std::vector<std::pair<StringRef, const InputSectionDescription *>>
LinkerScript<ELFT>::getSectionMap() {
std::vector<std::pair<StringRef, const InputSectionDescription *>> Ret;
for (const std::unique_ptr<BaseCommand> &Base1 : Opt.Commands)
if (auto *Cmd1 = dyn_cast<OutputSectionCommand>(Base1.get()))
for (const std::unique_ptr<BaseCommand> &Base2 : Cmd1->Commands)
if (auto *Cmd2 = dyn_cast<InputSectionDescription>(Base2.get()))
Ret.emplace_back(Cmd1->Name, Cmd2);
return Ret;
}
static bool fileMatches(const InputSectionDescription *Desc,
StringRef Filename) {
if (!globMatch(Desc->FilePattern, Filename))
@ -121,18 +136,101 @@ LinkerScript<ELFT>::getInputSections(const InputSectionDescription *I) {
return Ret;
}
// Add input section to output section. If there is no output section yet,
// then create it and add to output section list.
namespace {
template <class ELFT> class LayoutInputSection : public InputSection<ELFT> {
public:
LayoutInputSection(SymbolAssignment *Cmd);
static bool classof(const InputSectionBase<ELFT> *S);
SymbolAssignment *Cmd;
private:
typename ELFT::Shdr Hdr;
};
// Helper class, which builds output section list, also
// creating symbol sections, when needed
template <class ELFT> class OutputSectionBuilder {
public:
OutputSectionBuilder(OutputSectionFactory<ELFT> &F,
std::vector<OutputSectionBase<ELFT> *> *Out)
: Factory(F), OutputSections(Out) {}
void addSection(StringRef OutputName, InputSectionBase<ELFT> *I);
void addSymbol(SymbolAssignment *Cmd) {
PendingSymbols.emplace_back(new LayoutInputSection<ELFT>(Cmd));
}
void flushSymbols();
void flushSection();
void finalize();
private:
OutputSectionFactory<ELFT> &Factory;
std::vector<OutputSectionBase<ELFT> *> *OutputSections;
OutputSectionBase<ELFT> *Current = nullptr;
std::vector<std::unique_ptr<LayoutInputSection<ELFT>>> PendingSymbols;
static std::vector<std::unique_ptr<LayoutInputSection<ELFT>>> OwningSections;
};
template <class ELFT>
static void addSection(OutputSectionFactory<ELFT> &Factory,
std::vector<OutputSectionBase<ELFT> *> &Out,
InputSectionBase<ELFT> *C, StringRef Name) {
OutputSectionBase<ELFT> *Sec;
std::vector<std::unique_ptr<LayoutInputSection<ELFT>>>
OutputSectionBuilder<ELFT>::OwningSections;
}
template <class T> static T *zero(T *Val) {
memset(Val, 0, sizeof(*Val));
return Val;
}
template <class ELFT>
LayoutInputSection<ELFT>::LayoutInputSection(SymbolAssignment *Cmd)
: InputSection<ELFT>(nullptr, zero(&Hdr)), Cmd(Cmd) {
this->Live = true;
this->SectionKind = InputSectionBase<ELFT>::Layout;
Hdr.sh_type = SHT_NOBITS;
}
template <class ELFT>
bool LayoutInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == InputSectionBase<ELFT>::Layout;
}
template <class ELFT>
void OutputSectionBuilder<ELFT>::addSection(StringRef OutputName,
InputSectionBase<ELFT> *C) {
bool IsNew;
std::tie(Sec, IsNew) = Factory.create(C, Name);
std::tie(Current, IsNew) = Factory.create(C, OutputName);
if (IsNew)
Out.push_back(Sec);
Sec->addSection(C);
OutputSections->push_back(Current);
flushSymbols();
Current->addSection(C);
}
template <class ELFT> void OutputSectionBuilder<ELFT>::flushSymbols() {
for (std::unique_ptr<LayoutInputSection<ELFT>> &I : PendingSymbols)
if (I->Cmd->Name == "." || addSymbolToSymtab<ELFT>(*I->Cmd, 0, Current)) {
// Only regular output sections are supported.
if (dyn_cast_or_null<OutputSection<ELFT>>(Current)) {
Current->addSection(I.get());
OwningSections.push_back(std::move(I));
}
}
PendingSymbols.clear();
}
template <class ELFT> void OutputSectionBuilder<ELFT>::flushSection() {
flushSymbols();
Current = nullptr;
}
template <class ELFT> void OutputSectionBuilder<ELFT>::finalize() {
// Assign offsets to all sections which don't contain symbols
for (OutputSectionBase<ELFT> *S : *OutputSections)
if (llvm::find_if(OwningSections,
[&](std::unique_ptr<LayoutInputSection<ELFT>> &L) {
return L->OutSec == S;
}) == OwningSections.end())
S->assignOffsets();
}
template <class ELFT>
@ -160,28 +258,38 @@ getComparator(SortKind K) {
template <class ELFT>
void LinkerScript<ELFT>::createSections(
OutputSectionFactory<ELFT> &Factory) {
for (auto &P : getSectionMap()) {
StringRef OutputName = P.first;
const InputSectionDescription *Cmd = P.second;
std::vector<InputSectionBase<ELFT> *> Sections = getInputSections(Cmd);
OutputSectionBuilder<ELFT> Builder(Factory, OutputSections);
auto Add = [&](StringRef OutputName, const InputSectionDescription *Cmd) {
std::vector<InputSectionBase<ELFT> *> Sections = getInputSections(Cmd);
if (OutputName == "/DISCARD/") {
for (InputSectionBase<ELFT> *S : Sections) {
S->Live = false;
reportDiscarded(S);
}
continue;
return;
}
if (Cmd->SortInner)
std::stable_sort(Sections.begin(), Sections.end(),
getComparator<ELFT>(Cmd->SortInner));
if (Cmd->SortOuter)
std::stable_sort(Sections.begin(), Sections.end(),
getComparator<ELFT>(Cmd->SortOuter));
for (InputSectionBase<ELFT> *S : Sections)
addSection(Factory, *OutputSections, S, OutputName);
Builder.addSection(OutputName, S);
};
for (const std::unique_ptr<BaseCommand> &Base1 : Opt.Commands)
if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base1.get())) {
for (const std::unique_ptr<BaseCommand> &Base2 : Cmd->Commands)
if (auto *Assignment = dyn_cast<SymbolAssignment>(Base2.get()))
Builder.addSymbol(Assignment);
else
Add(Cmd->Name, cast<InputSectionDescription>(Base2.get()));
Builder.flushSection();
} else if (auto *Cmd2 = dyn_cast<SymbolAssignment>(Base1.get())) {
addSymbolToSymtab<ELFT>(*Cmd2, STV_DEFAULT);
}
// Add all other input sections, which are not listed in script.
@ -189,11 +297,12 @@ void LinkerScript<ELFT>::createSections(
Symtab<ELFT>::X->getObjectFiles())
for (InputSectionBase<ELFT> *S : F->getSections())
if (!isDiscarded(S) && !S->OutSec)
addSection(Factory, *OutputSections, S, getOutputSectionName(S));
Builder.addSection(getOutputSectionName(S), S);
// Remove from the output all the sections which did not meet
// the optional constraints.
filter();
Builder.finalize();
}
template <class R, class T>
@ -224,6 +333,35 @@ template <class ELFT> void LinkerScript<ELFT>::filter() {
}
}
template <class ELFT> void assignOffsets(OutputSectionBase<ELFT> *Sec) {
// Non-zero size means we have assigned offsets earlier in
// OutputSectionBuilder<ELFT>::finalize
auto *OutSec = dyn_cast<OutputSection<ELFT>>(Sec);
if (Sec->getSize() || !OutSec)
return;
typedef typename ELFT::uint uintX_t;
uintX_t Off = 0;
for (InputSection<ELFT> *I : OutSec->Sections) {
if (auto *L = dyn_cast<LayoutInputSection<ELFT>>(I)) {
uintX_t Value = L->Cmd->Expression(Sec->getVA() + Off) - Sec->getVA();
if (L->Cmd->Name == ".")
Off = Value;
else
cast<DefinedSynthetic<ELFT>>(L->Cmd->Sym)->Value = Value;
} else {
Off = alignTo(Off, I->Alignment);
I->OutSecOff = Off;
Off += I->getSize();
}
// Update section size inside for-loop, so that SIZEOF
// works correctly in the case below:
// .foo { *(.aaa) a = SIZEOF(.foo); *(.bbb) }
Sec->setSize(Off);
}
}
template <class ELFT> void LinkerScript<ELFT>::assignAddresses() {
ArrayRef<OutputSectionBase<ELFT> *> Sections = *OutputSections;
// Orphan sections are sections present in the input files which
@ -275,6 +413,7 @@ template <class ELFT> void LinkerScript<ELFT>::assignAddresses() {
uintX_t TVA = Dot + ThreadBssOffset;
TVA = alignTo(TVA, Sec->getAlignment());
Sec->setVA(TVA);
assignOffsets(Sec);
ThreadBssOffset = TVA - Dot + Sec->getSize();
continue;
}
@ -282,6 +421,7 @@ template <class ELFT> void LinkerScript<ELFT>::assignAddresses() {
if (Sec->getFlags() & SHF_ALLOC) {
Dot = alignTo(Dot, Sec->getAlignment());
Sec->setVA(Dot);
assignOffsets(Sec);
MinVA = std::min(MinVA, Dot);
Dot += Sec->getSize();
continue;
@ -395,28 +535,6 @@ int LinkerScript<ELFT>::compareSections(StringRef A, StringRef B) {
return I < J ? -1 : 1;
}
// Add symbols defined by linker scripts.
template <class ELFT> void LinkerScript<ELFT>::addScriptedSymbols() {
for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands) {
auto *Cmd = dyn_cast<SymbolAssignment>(Base.get());
if (!Cmd || Cmd->Name == ".")
continue;
// If a symbol was in PROVIDE(), define it only when it is an
// undefined symbol.
SymbolBody *B = Symtab<ELFT>::X->find(Cmd->Name);
if (Cmd->Provide && !(B && B->isUndefined()))
continue;
// Define an absolute symbol. The symbol value will be assigned later.
// (At this point, we don't know the final address yet.)
Symbol *Sym = Symtab<ELFT>::X->addUndefined(Cmd->Name);
replaceBody<DefinedRegular<ELFT>>(Sym, Cmd->Name, STV_DEFAULT);
Sym->Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT;
Cmd->Sym = Sym->body();
}
}
template <class ELFT> bool LinkerScript<ELFT>::hasPhdrsCommands() {
return !Opt.PhdrsCommands.empty();
}
@ -499,6 +617,7 @@ private:
unsigned readPhdrType();
SortKind readSortKind();
SymbolAssignment *readProvide(bool Hidden);
SymbolAssignment *readProvideOrAssignment(StringRef Tok);
Expr readAlign();
void readSort();
Expr readAssert();
@ -688,17 +807,11 @@ void ScriptParser::readSections() {
expect("{");
while (!Error && !skip("}")) {
StringRef Tok = next();
BaseCommand *Cmd;
if (peek() == "=" || peek() == "+=") {
Cmd = readAssignment(Tok);
expect(";");
} else if (Tok == "PROVIDE") {
Cmd = readProvide(false);
} else if (Tok == "PROVIDE_HIDDEN") {
Cmd = readProvide(true);
} else if (Tok == "ASSERT") {
BaseCommand *Cmd = readProvideOrAssignment(Tok);
if (!Cmd) {
if (Tok == "ASSERT")
Cmd = new AssertCommand(readAssert());
} else {
else
Cmd = readOutputSectionDescription(Tok);
}
Opt.Commands.emplace_back(Cmd);
@ -836,11 +949,14 @@ ScriptParser::readOutputSectionDescription(StringRef OutSec) {
Cmd->Commands.emplace_back(readInputSectionDescription());
continue;
}
if (skip("SORT")) {
StringRef Tok = next();
if (SymbolAssignment *Assignment = readProvideOrAssignment(Tok))
Cmd->Commands.emplace_back(Assignment);
else if (Tok == "SORT")
readSort();
continue;
}
setError("unknown command " + peek());
else
setError("unknown command " + Tok);
}
Cmd->Phdrs = readOutputSectionPhdrs();
Cmd->Filler = readOutputSectionFiller();
@ -877,6 +993,19 @@ SymbolAssignment *ScriptParser::readProvide(bool Hidden) {
return Cmd;
}
SymbolAssignment *ScriptParser::readProvideOrAssignment(StringRef Tok) {
SymbolAssignment *Cmd = nullptr;
if (peek() == "=" || peek() == "+=") {
Cmd = readAssignment(Tok);
expect(";");
} else if (Tok == "PROVIDE") {
Cmd = readProvide(false);
} else if (Tok == "PROVIDE_HIDDEN") {
Cmd = readProvide(true);
}
return Cmd;
}
static uint64_t getSymbolValue(StringRef S, uint64_t Dot) {
if (S == ".")
return Dot;

4
lld/ELF/LinkerScript.h
View File

@ -146,7 +146,6 @@ public:
bool shouldKeep(InputSectionBase<ELFT> *S);
void assignAddresses();
int compareSections(StringRef A, StringRef B);
void addScriptedSymbols();
bool hasPhdrsCommands();
uintX_t getOutputSectionSize(StringRef Name);
uintX_t getSizeOfHeaders();
@ -154,9 +153,6 @@ public:
std::vector<OutputSectionBase<ELFT> *> *OutputSections;
private:
std::vector<std::pair<StringRef, const InputSectionDescription *>>
getSectionMap();
std::vector<InputSectionBase<ELFT> *>
getInputSections(const InputSectionDescription *);

2
lld/ELF/OutputSections.cpp
View File

@ -1762,6 +1762,8 @@ OutputSectionFactory<ELFT>::create(InputSectionBase<ELFT> *C,
case InputSectionBase<ELFT>::MipsOptions:
Sec = new MipsOptionsOutputSection<ELFT>();
break;
case InputSectionBase<ELFT>::Layout:
llvm_unreachable("Invalid section type");
}
OwningSections.emplace_back(Sec);
return {Sec, true};

2
lld/ELF/Symbols.cpp
View File

@ -58,7 +58,7 @@ static typename ELFT::uint getSymVA(const SymbolBody &Body,
Offset += Addend;
Addend = 0;
}
uintX_t VA = SC->OutSec->getVA() + SC->getOffset(Offset);
uintX_t VA = (SC->OutSec ? SC->OutSec->getVA() : 0) + SC->getOffset(Offset);
if (D.isTls())
return VA - Out<ELFT>::TlsPhdr->p_vaddr;
return VA;

27
lld/ELF/Writer.cpp
View File

@ -238,6 +238,9 @@ template <class ELFT> void Writer<ELFT>::run() {
copyLocalSymbols();
addReservedSymbols();
if (Target->NeedsThunks)
forEachRelSec(createThunks<ELFT>);
CommonInputSection<ELFT> Common(getCommonSymbols<ELFT>());
CommonInputSection<ELFT>::X = &Common;
@ -659,6 +662,14 @@ template <class ELFT> void Writer<ELFT>::createSections() {
Sec->addSection(C);
}
}
sortInitFini(findSection(".init_array"));
sortInitFini(findSection(".fini_array"));
sortCtorsDtors(findSection(".ctors"));
sortCtorsDtors(findSection(".dtors"));
for (OutputSectionBase<ELFT> *Sec : OutputSections)
Sec->assignOffsets();
}
// Create output section objects and add them to OutputSections.
@ -667,12 +678,6 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
Out<ELFT>::InitArray = findSection(".init_array");
Out<ELFT>::FiniArray = findSection(".fini_array");
// Sort section contents for __attribute__((init_priority(N)).
sortInitFini(Out<ELFT>::InitArray);
sortInitFini(Out<ELFT>::FiniArray);
sortCtorsDtors(findSection(".ctors"));
sortCtorsDtors(findSection(".dtors"));
// The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
// symbols for sections, so that the runtime can get the start and end
// addresses of each section by section name. Add such symbols.
@ -692,21 +697,11 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
// Define __rel[a]_iplt_{start,end} symbols if needed.
addRelIpltSymbols();
// Add scripted symbols with zero values now.
// Real values will be assigned later
Script<ELFT>::X->addScriptedSymbols();
if (!Out<ELFT>::EhFrame->empty()) {
OutputSections.push_back(Out<ELFT>::EhFrame);
Out<ELFT>::EhFrame->finalize();
}
if (Target->NeedsThunks)
forEachRelSec(createThunks<ELFT>);
for (OutputSectionBase<ELFT> *Sec : OutputSections)
Sec->assignOffsets();
// Scan relocations. This must be done after every symbol is declared so that
// we can correctly decide if a dynamic relocation is needed.
forEachRelSec(scanRelocations<ELFT>);

38
lld/test/ELF/linkerscript/linkerscript-symbols-synthetic.s Normal file
View File

@ -0,0 +1,38 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
# Simple symbol assignment within input section list. The '.' symbol
# is not location counter but offset from the beginning of output
# section .foo
# RUN: echo "SECTIONS { \
# RUN: .foo : { \
# RUN: begin_foo = .; \
# RUN: *(.foo) \
# RUN: end_foo = .; \
# RUN: size_foo_1 = SIZEOF(.foo); \
# RUN: . = ALIGN(0x1000); \
# RUN: begin_bar = .; \
# RUN: *(.bar) \
# RUN: end_bar = .; \
# RUN: size_foo_2 = SIZEOF(.foo); \
# RUN: } \
# RUN: size_foo_3 = SIZEOF(.foo); }" > %t.script
# RUN: ld.lld -o %t1 --script %t.script %t
# RUN: llvm-objdump -t %t1 | FileCheck --check-prefix=SIMPLE %s
# SIMPLE: 0000000000000120 .foo 00000000 begin_foo
# SIMPLE-NEXT: 0000000000000128 .foo 00000000 end_foo
# SIMPLE-NEXT: 0000000000000008 .foo 00000000 size_foo_1
# SIMPLE-NEXT: 0000000000001000 .foo 00000000 begin_bar
# SIMPLE-NEXT: 0000000000001004 .foo 00000000 end_bar
# SIMPLE-NEXT: 0000000000000ee4 .foo 00000000 size_foo_2
# SIMPLE-NEXT: 0000000000000ee4 *ABS* 00000000 size_foo_3
.global _start
_start:
nop
.section .foo,"a"
.quad 0
.section .bar,"a"
.long 0