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[ELF2] SECTIONS command basic support 

* determine output section by input section name
* discard input sections
* order output sections accordingly

Differential Revision: http://reviews.llvm.org/D14140

llvm-svn: 252868
This commit is contained in:
Denis Protivensky 2015-11-12 09:52:08 +00:00
parent de8332257b
commit 8e3b38aba1
4 changed files with 207 additions and 11 deletions
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2
lld/ELF/Config.h
View File

@ -10,6 +10,7 @@
#ifndef LLD_ELF_CONFIG_H
#define LLD_ELF_CONFIG_H
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/ELF.h"
@ -41,6 +42,7 @@ struct Configuration {
llvm::StringRef SoName;
llvm::StringRef Sysroot;
std::string RPath;
llvm::MapVector<llvm::StringRef, std::vector<llvm::StringRef>> OutputSections;
std::vector<llvm::StringRef> SearchPaths;
std::vector<llvm::StringRef> Undefined;
bool AllowMultipleDefinition;

37
lld/ELF/LinkerScript.cpp
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@ -36,6 +36,7 @@ private:
static std::vector<StringRef> tokenize(StringRef S);
static StringRef skipSpace(StringRef S);
StringRef next();
bool skip(StringRef Tok);
bool atEOF() { return Tokens.size() == Pos; }
void expect(StringRef Expect);
@ -50,6 +51,9 @@ private:
void readOutputArch();
void readOutputFormat();
void readSearchDir();
void readSections();
void readOutputSectionDescription();
StringSaver Saver;
std::vector<StringRef> Tokens;
@ -78,6 +82,8 @@ void LinkerScript::run() {
readOutputFormat();
} else if (Tok == "SEARCH_DIR") {
readSearchDir();
} else if (Tok == "SECTIONS") {
readSections();
} else {
error("unknown directive: " + Tok);
}
@ -133,11 +139,20 @@ StringRef LinkerScript::skipSpace(StringRef S) {
}
StringRef LinkerScript::next() {
if (Pos == Tokens.size())
if (atEOF())
error("unexpected EOF");
return Tokens[Pos++];
}
bool LinkerScript::skip(StringRef Tok) {
if (atEOF())
error("unexpected EOF");
if (Tok != Tokens[Pos])
return false;
++Pos;
return true;
}
void LinkerScript::expect(StringRef Expect) {
StringRef Tok = next();
if (Tok != Expect)
@ -255,6 +270,26 @@ void LinkerScript::readSearchDir() {
expect(")");
}
void LinkerScript::readSections() {
expect("{");
while (!skip("}"))
readOutputSectionDescription();
}
void LinkerScript::readOutputSectionDescription() {
StringRef Name = next();
std::vector<StringRef> &InputSections = Config->OutputSections[Name];
expect(":");
expect("{");
while (!skip("}")) {
next(); // Skip input file name.
expect("(");
while (!skip(")"))
InputSections.push_back(next());
}
}
// Entry point. The other functions or classes are private to this file.
void lld::elf2::readLinkerScript(BumpPtrAllocator *A, MemoryBufferRef MB) {
LinkerScript(A, MB.getBuffer()).run();

60
lld/ELF/Writer.cpp
View File

@ -13,6 +13,7 @@
#include "SymbolTable.h"
#include "Target.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/FileOutputBuffer.h"
#include "llvm/Support/StringSaver.h"
@ -47,9 +48,12 @@ private:
void scanRelocs(InputSection<ELFT> &C);
void scanRelocs(InputSectionBase<ELFT> &S, const Elf_Shdr &RelSec);
void assignAddresses();
void buildSectionMap();
void openFile(StringRef OutputPath);
void writeHeader();
void writeSections();
bool isDiscarded(InputSectionBase<ELFT> *IS) const;
StringRef getOutputSectionName(StringRef S) const;
bool needsInterpSection() const {
return !Symtab.getSharedFiles().empty() && !Config->DynamicLinker.empty();
}
@ -82,6 +86,8 @@ private:
uintX_t FileSize;
uintX_t SectionHeaderOff;
llvm::StringMap<llvm::StringRef> InputToOutputSection;
};
} // anonymous namespace
@ -131,6 +137,7 @@ template <class ELFT> void lld::elf2::writeResult(SymbolTable<ELFT> *Symtab) {
// The main function of the writer.
template <class ELFT> void Writer<ELFT>::run() {
buildSectionMap();
if (!Config->DiscardAll)
copyLocalSymbols();
createSections();
@ -461,7 +468,12 @@ void Writer<ELFT>::addSharedCopySymbols(
Out<ELFT>::Bss->setSize(Off);
}
static StringRef getOutputName(StringRef S) {
template <class ELFT>
StringRef Writer<ELFT>::getOutputSectionName(StringRef S) const {
auto It = InputToOutputSection.find(S);
if (It != std::end(InputToOutputSection))
return It->second;
if (S.startswith(".text."))
return ".text";
if (S.startswith(".rodata."))
@ -473,6 +485,27 @@ static StringRef getOutputName(StringRef S) {
return S;
}
template <class ELFT>
bool Writer<ELFT>::isDiscarded(InputSectionBase<ELFT> *IS) const {
if (!IS || !IS->isLive() || IS == &InputSection<ELFT>::Discarded)
return true;
return InputToOutputSection.lookup(IS->getSectionName()) == "/DISCARD/";
}
template <class ELFT>
static bool compareSections(OutputSectionBase<ELFT> *A,
OutputSectionBase<ELFT> *B) {
auto ItA = Config->OutputSections.find(A->getName());
auto ItEnd = std::end(Config->OutputSections);
if (ItA == ItEnd)
return compareOutputSections(A, B);
auto ItB = Config->OutputSections.find(B->getName());
if (ItB == ItEnd)
return compareOutputSections(A, B);
return std::distance(ItA, ItB) > 0;
}
// Create output section objects and add them to OutputSections.
template <class ELFT> void Writer<ELFT>::createSections() {
// .interp needs to be on the first page in the output file.
@ -485,7 +518,7 @@ template <class ELFT> void Writer<ELFT>::createSections() {
for (const std::unique_ptr<ObjectFile<ELFT>> &F : Symtab.getObjectFiles()) {
for (InputSectionBase<ELFT> *C : F->getSections()) {
if (!C || !C->isLive() || C == &InputSection<ELFT>::Discarded)
if (isDiscarded(C))
continue;
const Elf_Shdr *H = C->getSectionHdr();
uintX_t OutFlags = H->sh_flags & ~SHF_GROUP;
@ -498,7 +531,7 @@ template <class ELFT> void Writer<ELFT>::createSections() {
if (OutType == SHT_PROGBITS && C->getSectionName() == ".eh_frame" &&
Config->EMachine == EM_X86_64)
OutType = SHT_X86_64_UNWIND;
SectionKey<ELFT::Is64Bits> Key{getOutputName(C->getSectionName()),
SectionKey<ELFT::Is64Bits> Key{getOutputSectionName(C->getSectionName()),
OutType, OutFlags, EntSize};
OutputSectionBase<ELFT> *&Sec = Map[Key];
if (!Sec) {
@ -577,14 +610,14 @@ template <class ELFT> void Writer<ELFT>::createSections() {
// Scan relocations. This must be done after every symbol is declared so that
// we can correctly decide if a dynamic relocation is needed.
for (const std::unique_ptr<ObjectFile<ELFT>> &F : Symtab.getObjectFiles()) {
for (InputSectionBase<ELFT> *B : F->getSections()) {
if (auto *S = dyn_cast_or_null<InputSection<ELFT>>(B)) {
if (S != &InputSection<ELFT>::Discarded && S->isLive())
scanRelocs(*S);
} else if (auto *S = dyn_cast_or_null<EHInputSection<ELFT>>(B)) {
for (InputSectionBase<ELFT> *C : F->getSections()) {
if (isDiscarded(C))
continue;
if (auto *S = dyn_cast<InputSection<ELFT>>(C))
scanRelocs(*S);
else if (auto *S = dyn_cast<EHInputSection<ELFT>>(C))
if (S->RelocSection)
scanRelocs(*S, *S->RelocSection);
}
}
}
@ -656,7 +689,7 @@ template <class ELFT> void Writer<ELFT>::createSections() {
OutputSections.push_back(Out<ELFT>::Plt);
std::stable_sort(OutputSections.begin(), OutputSections.end(),
compareOutputSections<ELFT>);
compareSections<ELFT>);
for (unsigned I = 0, N = OutputSections.size(); I < N; ++I)
OutputSections[I]->SectionIndex = I + 1;
@ -952,6 +985,13 @@ void Writer<ELFT>::copyPhdr(Elf_Phdr *PH, OutputSectionBase<ELFT> *From) {
PH->p_align = From->getAlign();
}
template <class ELFT> void Writer<ELFT>::buildSectionMap() {
for (const std::pair<StringRef, std::vector<StringRef>> &OutSec :
Config->OutputSections)
for (StringRef Name : OutSec.second)
InputToOutputSection[Name] = OutSec.first;
}
template void lld::elf2::writeResult<ELF32LE>(SymbolTable<ELF32LE> *Symtab);
template void lld::elf2::writeResult<ELF32BE>(SymbolTable<ELF32BE> *Symtab);
template void lld::elf2::writeResult<ELF64LE>(SymbolTable<ELF64LE> *Symtab);

119
lld/test/elf2/linkerscript-sections.s Normal file
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@ -0,0 +1,119 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
# Empty SECTIONS command.
# RUN: echo "SECTIONS {}" > %t.script
# RUN: ld.lld2 -o %t1 --script %t.script %t
# RUN: llvm-objdump -section-headers %t1 | \
# RUN: FileCheck -check-prefix=SEC-DEFAULT %s
# SECTIONS command with the same order as default.
# RUN: echo "SECTIONS { \
# RUN: .text : { *(.text) } \
# RUN: .data : { *(.data) } }" \ > %t.script
# RUN: ld.lld2 -o %t2 --script %t.script %t
# RUN: llvm-objdump -section-headers %t2 | \
# RUN: FileCheck -check-prefix=SEC-DEFAULT %s
# Idx Name Size
# SEC-DEFAULT: 1 .text 0000000e {{[0-9a-f]*}} TEXT DATA
# SEC-DEFAULT: 2 .data 00000020 {{[0-9a-f]*}} DATA
# SEC-DEFAULT: 3 other 00000003 {{[0-9a-f]*}} DATA
# SEC-DEFAULT: 4 .bss 00000002 {{[0-9a-f]*}} BSS
# SEC-DEFAULT: 5 .shstrtab 00000002 {{[0-9a-f]*}}
# SEC-DEFAULT: 6 .symtab 00000030 {{[0-9a-f]*}}
# SEC-DEFAULT: 7 .shstrtab 00000032 {{[0-9a-f]*}}
# SEC-DEFAULT: 8 .strtab 00000008 {{[0-9a-f]*}}
# Sections are put in order specified in linker script.
# RUN: echo "SECTIONS { \
# RUN: .bss : { *(.bss) } \
# RUN: other : { *(other) } \
# RUN: .shstrtab : { *(.shstrtab) } \
# RUN: .symtab : { *(.symtab) } \
# RUN: .strtab : { *(.strtab) } \
# RUN: .data : { *(.data) } \
# RUN: .text : { *(.text) } }" \ > %t.script
# RUN: ld.lld2 -o %t3 --script %t.script %t
# RUN: llvm-objdump -section-headers %t3 | \
# RUN: FileCheck -check-prefix=SEC-ORDER %s
# Idx Name Size
# SEC-ORDER: 1 .bss 00000002 {{[0-9a-f]*}} BSS
# SEC-ORDER: 2 other 00000003 {{[0-9a-f]*}} DATA
# SEC-ORDER: 3 .shstrtab 00000002 {{[0-9a-f]*}}
# SEC-ORDER: 4 .shstrtab 00000032 {{[0-9a-f]*}}
# SEC-ORDER: 5 .symtab 00000030 {{[0-9a-f]*}}
# SEC-ORDER: 6 .strtab 00000008 {{[0-9a-f]*}}
# SEC-ORDER: 7 .data 00000020 {{[0-9a-f]*}} DATA
# SEC-ORDER: 8 .text 0000000e {{[0-9a-f]*}} TEXT DATA
# .text and .data have swapped names but proper sizes and types.
# RUN: echo "SECTIONS { \
# RUN: .data : { *(.text) } \
# RUN: .text : { *(.data) } }" \ > %t.script
# RUN: ld.lld2 -o %t4 --script %t.script %t
# RUN: llvm-objdump -section-headers %t4 | \
# RUN: FileCheck -check-prefix=SEC-SWAP-NAMES %s
# Idx Name Size
# SEC-SWAP-NAMES: 1 .data 0000000e {{[0-9a-f]*}} TEXT DATA
# SEC-SWAP-NAMES: 2 .text 00000020 {{[0-9a-f]*}} DATA
# SEC-SWAP-NAMES: 3 other 00000003 {{[0-9a-f]*}} DATA
# SEC-SWAP-NAMES: 4 .bss 00000002 {{[0-9a-f]*}} BSS
# SEC-SWAP-NAMES: 5 .shstrtab 00000002 {{[0-9a-f]*}}
# SEC-SWAP-NAMES: 6 .symtab 00000030 {{[0-9a-f]*}}
# SEC-SWAP-NAMES: 7 .shstrtab 00000032 {{[0-9a-f]*}}
# SEC-SWAP-NAMES: 8 .strtab 00000008 {{[0-9a-f]*}}
# .shstrtab from the input object file is discarded.
# RUN: echo "SECTIONS { \
# RUN: /DISCARD/ : { *(.shstrtab) } }" \ > %t.script
# RUN: ld.lld2 -o %t5 --script %t.script %t
# RUN: llvm-objdump -section-headers %t5 | \
# RUN: FileCheck -check-prefix=SEC-DISCARD %s
# Idx Name Size
# SEC-DISCARD: 1 .text 0000000e {{[0-9a-f]*}} TEXT DATA
# SEC-DISCARD: 2 .data 00000020 {{[0-9a-f]*}} DATA
# SEC-DISCARD: 3 other 00000003 {{[0-9a-f]*}} DATA
# SEC-DISCARD: 4 .bss 00000002 {{[0-9a-f]*}} BSS
# SEC-DISCARD: 5 .symtab 00000030 {{[0-9a-f]*}}
# SEC-DISCARD: 6 .shstrtab 00000032 {{[0-9a-f]*}}
# SEC-DISCARD: 7 .strtab 00000008 {{[0-9a-f]*}}
# Multiple SECTIONS command specifying additional input section descriptions
# for the same output section description - input sections are merged into
# one output section.
# RUN: echo "SECTIONS { \
# RUN: .text : { *(.text) } \
# RUN: .data : { *(.data) } } \
# RUN: SECTIONS { \
# RUN: .data : { *(other) } }" \ > %t.script
# RUN: ld.lld2 -o %t6 --script %t.script %t
# RUN: llvm-objdump -section-headers %t6 | \
# RUN: FileCheck -check-prefix=SEC-MULTI %s
# Idx Name Size
# SEC-MULTI: 1 .text 0000000e {{[0-9a-f]*}} TEXT DATA
# SEC-MULTI: 2 .data 00000023 {{[0-9a-f]*}} DATA
# SEC-MULTI: 3 .bss 00000002 {{[0-9a-f]*}} BSS
# SEC-MULTI: 4 .shstrtab 00000002 {{[0-9a-f]*}}
# SEC-MULTI: 5 .symtab 00000030 {{[0-9a-f]*}}
# SEC-MULTI: 6 .shstrtab 0000002c {{[0-9a-f]*}}
# SEC-MULTI: 7 .strtab 00000008 {{[0-9a-f]*}}
.globl _start;
_start:
mov $60, %rax
mov $42, %rdi
.section .data,"aw"
.quad 10, 10, 20, 20
.section other,"aw"
.short 10
.byte 20
.section .shstrtab,""
.short 20
.section .bss,"",@nobits
.short 0