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+//===-- ELFWriter.cpp - Target-independent ELF Writer code ----------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the target-independent ELF writer. This file writes out
+// the ELF file in the following order:
+//
+// #1. ELF Header
+// #2. '.text' section
+// #3. '.data' section
+// #4. '.bss' section (conceptual position in file)
+// ...
+// #X. '.shstrtab' section
+// #Y. Section Table
+//
+// The entries in the section table are laid out as:
+// #0. Null entry [required]
+// #1. ".text" entry - the program code
+// #2. ".data" entry - global variables with initializers. [ if needed ]
+// #3. ".bss" entry - global variables without initializers. [ if needed ]
+// ...
+// #N. ".shstrtab" entry - String table for the section names.
+//
+// NOTE: This code should eventually be extended to support 64-bit ELF (this
+// won't be hard), but we haven't done so yet!
+//
+//===----------------------------------------------------------------------===//
+
+#include "ELFWriter.h"
+#include "llvm/Module.h"
+#include "llvm/PassManager.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/CodeGen/FileWriters.h"
+#include "llvm/CodeGen/MachineCodeEmitter.h"
+#include "llvm/CodeGen/MachineConstantPool.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Target/TargetELFWriterInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Support/Mangler.h"
+#include "llvm/Support/OutputBuffer.h"
+#include "llvm/Support/Streams.h"
+#include "llvm/Support/raw_ostream.h"
+#include <list>
+using namespace llvm;
+
+char ELFWriter::ID = 0;
+/// AddELFWriter - Concrete function to add the ELF writer to the function pass
+/// manager.
+MachineCodeEmitter *llvm::AddELFWriter(PassManagerBase &PM,
+ raw_ostream &O,
+ TargetMachine &TM) {
+ ELFWriter *EW = new ELFWriter(O, TM);
+ PM.add(EW);
+ return &EW->getMachineCodeEmitter();
+}
+
+//===----------------------------------------------------------------------===//
+// ELFCodeEmitter Implementation
+//===----------------------------------------------------------------------===//
+
+namespace llvm {
+ /// ELFCodeEmitter - This class is used by the ELFWriter to emit the code for
+ /// functions to the ELF file.
+ class ELFCodeEmitter : public MachineCodeEmitter {
+ ELFWriter &EW;
+ TargetMachine &TM;
+ ELFWriter::ELFSection *ES; // Section to write to.
+ std::vector<unsigned char> *OutBuffer;
+ size_t FnStart;
+ public:
+ explicit ELFCodeEmitter(ELFWriter &ew) : EW(ew), TM(EW.TM), OutBuffer(0) {}
+
+ void startFunction(MachineFunction &F);
+ bool finishFunction(MachineFunction &F);
+
+ void addRelocation(const MachineRelocation &MR) {
+ assert(0 && "relo not handled yet!");
+ }
+
+ virtual void StartMachineBasicBlock(MachineBasicBlock *MBB) {
+ }
+
+ virtual uintptr_t getConstantPoolEntryAddress(unsigned Index) const {
+ assert(0 && "CP not implementated yet!");
+ return 0;
+ }
+ virtual uintptr_t getJumpTableEntryAddress(unsigned Index) const {
+ assert(0 && "JT not implementated yet!");
+ return 0;
+ }
+
+ virtual uintptr_t getMachineBasicBlockAddress(MachineBasicBlock *MBB) const {
+ assert(0 && "JT not implementated yet!");
+ return 0;
+ }
+
+ virtual uintptr_t getLabelAddress(uint64_t Label) const {
+ assert(0 && "Label address not implementated yet!");
+ abort();
+ return 0;
+ }
+
+ virtual void emitLabel(uint64_t LabelID) {
+ assert(0 && "emit Label not implementated yet!");
+ abort();
+ }
+
+
+ virtual void setModuleInfo(llvm::MachineModuleInfo* MMI) { }
+
+
+ /// JIT SPECIFIC FUNCTIONS - DO NOT IMPLEMENT THESE HERE!
+ void startGVStub(const GlobalValue* F, unsigned StubSize,
+ unsigned Alignment = 1) {
+ assert(0 && "JIT specific function called!");
+ abort();
+ }
+ void startGVStub(const GlobalValue* F, void *Buffer, unsigned StubSize) {
+ assert(0 && "JIT specific function called!");
+ abort();
+ }
+ void *finishGVStub(const GlobalValue *F) {
+ assert(0 && "JIT specific function called!");
+ abort();
+ return 0;
+ }
+ };
+}
+
+/// startFunction - This callback is invoked when a new machine function is
+/// about to be emitted.
+void ELFCodeEmitter::startFunction(MachineFunction &F) {
+ // Align the output buffer to the appropriate alignment.
+ unsigned Align = 16; // FIXME: GENERICIZE!!
+ // Get the ELF Section that this function belongs in.
+ ES = &EW.getSection(".text", ELFWriter::ELFSection::SHT_PROGBITS,
+ ELFWriter::ELFSection::SHF_EXECINSTR |
+ ELFWriter::ELFSection::SHF_ALLOC);
+ OutBuffer = &ES->SectionData;
+ cerr << "FIXME: This code needs to be updated for changes in the "
+ << "CodeEmitter interfaces. In particular, this should set "
+ << "BufferBegin/BufferEnd/CurBufferPtr, not deal with OutBuffer!";
+ abort();
+
+ // Upgrade the section alignment if required.
+ if (ES->Align < Align) ES->Align = Align;
+
+ // Add padding zeros to the end of the buffer to make sure that the
+ // function will start on the correct byte alignment within the section.
+ OutputBuffer OB(*OutBuffer,
+ TM.getTargetData()->getPointerSizeInBits() == 64,
+ TM.getTargetData()->isLittleEndian());
+ OB.align(Align);
+ FnStart = OutBuffer->size();
+}
+
+/// finishFunction - This callback is invoked after the function is completely
+/// finished.
+bool ELFCodeEmitter::finishFunction(MachineFunction &F) {
+ // We now know the size of the function, add a symbol to represent it.
+ ELFWriter::ELFSym FnSym(F.getFunction());
+
+ // Figure out the binding (linkage) of the symbol.
+ switch (F.getFunction()->getLinkage()) {
+ default:
+ // appending linkage is illegal for functions.
+ assert(0 && "Unknown linkage type!");
+ case GlobalValue::ExternalLinkage:
+ FnSym.SetBind(ELFWriter::ELFSym::STB_GLOBAL);
+ break;
+ case GlobalValue::LinkOnceAnyLinkage:
+ case GlobalValue::LinkOnceODRLinkage:
+ case GlobalValue::WeakAnyLinkage:
+ case GlobalValue::WeakODRLinkage:
+ FnSym.SetBind(ELFWriter::ELFSym::STB_WEAK);
+ break;
+ case GlobalValue::PrivateLinkage:
+ assert (0 && "PrivateLinkage should not be in the symbol table.");
+ case GlobalValue::InternalLinkage:
+ FnSym.SetBind(ELFWriter::ELFSym::STB_LOCAL);
+ break;
+ }
+
+ ES->Size = OutBuffer->size();
+
+ FnSym.SetType(ELFWriter::ELFSym::STT_FUNC);
+ FnSym.SectionIdx = ES->SectionIdx;
+ FnSym.Value = FnStart; // Value = Offset from start of Section.
+ FnSym.Size = OutBuffer->size()-FnStart;
+
+ // Finally, add it to the symtab.
+ EW.SymbolTable.push_back(FnSym);
+ return false;
+}
+
+//===----------------------------------------------------------------------===//
+// ELFWriter Implementation
+//===----------------------------------------------------------------------===//
+
+ELFWriter::ELFWriter(raw_ostream &o, TargetMachine &tm)
+ : MachineFunctionPass(&ID), O(o), TM(tm) {
+ e_flags = 0; // e_flags defaults to 0, no flags.
+
+ is64Bit = TM.getTargetData()->getPointerSizeInBits() == 64;
+ isLittleEndian = TM.getTargetData()->isLittleEndian();
+
+ // Create the machine code emitter object for this target.
+ MCE = new ELFCodeEmitter(*this);
+ NumSections = 0;
+}
+
+ELFWriter::~ELFWriter() {
+ delete MCE;
+}
+
+// doInitialization - Emit the file header and all of the global variables for
+// the module to the ELF file.
+bool ELFWriter::doInitialization(Module &M) {
+ Mang = new Mangler(M);
+
+ // Local alias to shortenify coming code.
+ std::vector<unsigned char> &FH = FileHeader;
+ OutputBuffer FHOut(FH, is64Bit, isLittleEndian);
+
+ FHOut.outbyte(0x7F); // EI_MAG0
+ FHOut.outbyte('E'); // EI_MAG1
+ FHOut.outbyte('L'); // EI_MAG2
+ FHOut.outbyte('F'); // EI_MAG3
+ FHOut.outbyte(is64Bit ? 2 : 1); // EI_CLASS
+ FHOut.outbyte(isLittleEndian ? 1 : 2); // EI_DATA
+ FHOut.outbyte(1); // EI_VERSION
+ FH.resize(16); // EI_PAD up to 16 bytes.
+
+ // This should change for shared objects.
+ FHOut.outhalf(1); // e_type = ET_REL
+ FHOut.outhalf(TM.getELFWriterInfo()->getEMachine()); // target-defined
+ FHOut.outword(1); // e_version = 1
+ FHOut.outaddr(0); // e_entry = 0 -> no entry point in .o file
+ FHOut.outaddr(0); // e_phoff = 0 -> no program header for .o
+
+ ELFHeader_e_shoff_Offset = FH.size();
+ FHOut.outaddr(0); // e_shoff
+ FHOut.outword(e_flags); // e_flags = whatever the target wants
+
+ FHOut.outhalf(is64Bit ? 64 : 52); // e_ehsize = ELF header size
+ FHOut.outhalf(0); // e_phentsize = prog header entry size
+ FHOut.outhalf(0); // e_phnum = # prog header entries = 0
+ FHOut.outhalf(is64Bit ? 64 : 40); // e_shentsize = sect hdr entry size
+
+
+ ELFHeader_e_shnum_Offset = FH.size();
+ FHOut.outhalf(0); // e_shnum = # of section header ents
+ ELFHeader_e_shstrndx_Offset = FH.size();
+ FHOut.outhalf(0); // e_shstrndx = Section # of '.shstrtab'
+
+ // Add the null section, which is required to be first in the file.
+ getSection("", 0, 0);
+
+ // Start up the symbol table. The first entry in the symtab is the null
+ // entry.
+ SymbolTable.push_back(ELFSym(0));
+
+ return false;
+}
+
+void ELFWriter::EmitGlobal(GlobalVariable *GV) {
+ // If this is an external global, emit it now. TODO: Note that it would be
+ // better to ignore the symbol here and only add it to the symbol table if
+ // referenced.
+ if (!GV->hasInitializer()) {
+ ELFSym ExternalSym(GV);
+ ExternalSym.SetBind(ELFSym::STB_GLOBAL);
+ ExternalSym.SetType(ELFSym::STT_NOTYPE);
+ ExternalSym.SectionIdx = ELFSection::SHN_UNDEF;
+ SymbolTable.push_back(ExternalSym);
+ return;
+ }
+
+ unsigned Align = TM.getTargetData()->getPreferredAlignment(GV);
+ unsigned Size =
+ TM.getTargetData()->getTypeAllocSize(GV->getType()->getElementType());
+
+ // If this global has a zero initializer, it is part of the .bss or common
+ // section.
+ if (GV->getInitializer()->isNullValue()) {
+ // If this global is part of the common block, add it now. Variables are
+ // part of the common block if they are zero initialized and allowed to be
+ // merged with other symbols.
+ if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage() ||
+ GV->hasCommonLinkage()) {
+ ELFSym CommonSym(GV);
+ // Value for common symbols is the alignment required.
+ CommonSym.Value = Align;
+ CommonSym.Size = Size;
+ CommonSym.SetBind(ELFSym::STB_GLOBAL);
+ CommonSym.SetType(ELFSym::STT_OBJECT);
+ // TODO SOMEDAY: add ELF visibility.
+ CommonSym.SectionIdx = ELFSection::SHN_COMMON;
+ SymbolTable.push_back(CommonSym);
+ return;
+ }
+
+ // Otherwise, this symbol is part of the .bss section. Emit it now.
+
+ // Handle alignment. Ensure section is aligned at least as much as required
+ // by this symbol.
+ ELFSection &BSSSection = getBSSSection();
+ BSSSection.Align = std::max(BSSSection.Align, Align);
+
+ // Within the section, emit enough virtual padding to get us to an alignment
+ // boundary.
+ if (Align)
+ BSSSection.Size = (BSSSection.Size + Align - 1) & ~(Align-1);
+
+ ELFSym BSSSym(GV);
+ BSSSym.Value = BSSSection.Size;
+ BSSSym.Size = Size;
+ BSSSym.SetType(ELFSym::STT_OBJECT);
+
+ switch (GV->getLinkage()) {
+ default: // weak/linkonce/common handled above
+ assert(0 && "Unexpected linkage type!");
+ case GlobalValue::AppendingLinkage: // FIXME: This should be improved!
+ case GlobalValue::ExternalLinkage:
+ BSSSym.SetBind(ELFSym::STB_GLOBAL);
+ break;
+ case GlobalValue::InternalLinkage:
+ BSSSym.SetBind(ELFSym::STB_LOCAL);
+ break;
+ }
+
+ // Set the idx of the .bss section
+ BSSSym.SectionIdx = BSSSection.SectionIdx;
+ if (!GV->hasPrivateLinkage())
+ SymbolTable.push_back(BSSSym);
+
+ // Reserve space in the .bss section for this symbol.
+ BSSSection.Size += Size;
+ return;
+ }
+
+ // FIXME: handle .rodata
+ //assert(!GV->isConstant() && "unimp");
+
+ // FIXME: handle .data
+ //assert(0 && "unimp");
+}
+
+
+bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
+ // Nothing to do here, this is all done through the MCE object above.
+ return false;
+}
+
+/// doFinalization - Now that the module has been completely processed, emit
+/// the ELF file to 'O'.
+bool ELFWriter::doFinalization(Module &M) {
+ // Okay, the ELF header and .text sections have been completed, build the
+ // .data, .bss, and "common" sections next.
+ for (Module::global_iterator I = M.global_begin(), E = M.global_end();
+ I != E; ++I)
+ EmitGlobal(I);
+
+ // Emit the symbol table now, if non-empty.
+ EmitSymbolTable();
+
+ // FIXME: Emit the relocations now.
+
+ // Emit the string table for the sections in the ELF file we have.
+ EmitSectionTableStringTable();
+
+ // Emit the sections to the .o file, and emit the section table for the file.
+ OutputSectionsAndSectionTable();
+
+ // We are done with the abstract symbols.
+ SectionList.clear();
+ NumSections = 0;
+
+ // Release the name mangler object.
+ delete Mang; Mang = 0;
+ return false;
+}
+
+/// EmitSymbolTable - If the current symbol table is non-empty, emit the string
+/// table for it and then the symbol table itself.
+void ELFWriter::EmitSymbolTable() {
+ if (SymbolTable.size() == 1) return; // Only the null entry.
+
+ // FIXME: compact all local symbols to the start of the symtab.
+ unsigned FirstNonLocalSymbol = 1;
+
+ ELFSection &StrTab = getSection(".strtab", ELFSection::SHT_STRTAB, 0);
+ StrTab.Align = 1;
+
+ DataBuffer &StrTabBuf = StrTab.SectionData;
+ OutputBuffer StrTabOut(StrTabBuf, is64Bit, isLittleEndian);
+
+ // Set the zero'th symbol to a null byte, as required.
+ StrTabOut.outbyte(0);
+ SymbolTable[0].NameIdx = 0;
+ unsigned Index = 1;
+ for (unsigned i = 1, e = SymbolTable.size(); i != e; ++i) {
+ // Use the name mangler to uniquify the LLVM symbol.
+ std::string Name = Mang->getValueName(SymbolTable[i].GV);
+
+ if (Name.empty()) {
+ SymbolTable[i].NameIdx = 0;
+ } else {
+ SymbolTable[i].NameIdx = Index;
+
+ // Add the name to the output buffer, including the null terminator.
+ StrTabBuf.insert(StrTabBuf.end(), Name.begin(), Name.end());
+
+ // Add a null terminator.
+ StrTabBuf.push_back(0);
+
+ // Keep track of the number of bytes emitted to this section.
+ Index += Name.size()+1;
+ }
+ }
+ assert(Index == StrTabBuf.size());
+ StrTab.Size = Index;
+
+ // Now that we have emitted the string table and know the offset into the
+ // string table of each symbol, emit the symbol table itself.
+ ELFSection &SymTab = getSection(".symtab", ELFSection::SHT_SYMTAB, 0);
+ SymTab.Align = is64Bit ? 8 : 4;
+ SymTab.Link = SymTab.SectionIdx; // Section Index of .strtab.
+ SymTab.Info = FirstNonLocalSymbol; // First non-STB_LOCAL symbol.
+ SymTab.EntSize = 16; // Size of each symtab entry. FIXME: wrong for ELF64
+ DataBuffer &SymTabBuf = SymTab.SectionData;
+ OutputBuffer SymTabOut(SymTabBuf, is64Bit, isLittleEndian);
+
+ if (!is64Bit) { // 32-bit and 64-bit formats are shuffled a bit.
+ for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
+ ELFSym &Sym = SymbolTable[i];
+ SymTabOut.outword(Sym.NameIdx);
+ SymTabOut.outaddr32(Sym.Value);
+ SymTabOut.outword(Sym.Size);
+ SymTabOut.outbyte(Sym.Info);
+ SymTabOut.outbyte(Sym.Other);
+ SymTabOut.outhalf(Sym.SectionIdx);
+ }
+ } else {
+ for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
+ ELFSym &Sym = SymbolTable[i];
+ SymTabOut.outword(Sym.NameIdx);
+ SymTabOut.outbyte(Sym.Info);
+ SymTabOut.outbyte(Sym.Other);
+ SymTabOut.outhalf(Sym.SectionIdx);
+ SymTabOut.outaddr64(Sym.Value);
+ SymTabOut.outxword(Sym.Size);
+ }
+ }
+
+ SymTab.Size = SymTabBuf.size();
+}
+
+/// EmitSectionTableStringTable - This method adds and emits a section for the
+/// ELF Section Table string table: the string table that holds all of the
+/// section names.
+void ELFWriter::EmitSectionTableStringTable() {
+ // First step: add the section for the string table to the list of sections:
+ ELFSection &SHStrTab = getSection(".shstrtab", ELFSection::SHT_STRTAB, 0);
+
+ // Now that we know which section number is the .shstrtab section, update the
+ // e_shstrndx entry in the ELF header.
+ OutputBuffer FHOut(FileHeader, is64Bit, isLittleEndian);
+ FHOut.fixhalf(SHStrTab.SectionIdx, ELFHeader_e_shstrndx_Offset);
+
+ // Set the NameIdx of each section in the string table and emit the bytes for
+ // the string table.
+ unsigned Index = 0;
+ DataBuffer &Buf = SHStrTab.SectionData;
+
+ for (std::list<ELFSection>::iterator I = SectionList.begin(),
+ E = SectionList.end(); I != E; ++I) {
+ // Set the index into the table. Note if we have lots of entries with
+ // common suffixes, we could memoize them here if we cared.
+ I->NameIdx = Index;
+
+ // Add the name to the output buffer, including the null terminator.
+ Buf.insert(Buf.end(), I->Name.begin(), I->Name.end());
+
+ // Add a null terminator.
+ Buf.push_back(0);
+
+ // Keep track of the number of bytes emitted to this section.
+ Index += I->Name.size()+1;
+ }
+
+ // Set the size of .shstrtab now that we know what it is.
+ assert(Index == Buf.size());
+ SHStrTab.Size = Index;
+}
+
+/// OutputSectionsAndSectionTable - Now that we have constructed the file header
+/// and all of the sections, emit these to the ostream destination and emit the
+/// SectionTable.
+void ELFWriter::OutputSectionsAndSectionTable() {
+ // Pass #1: Compute the file offset for each section.
+ size_t FileOff = FileHeader.size(); // File header first.
+
+ // Emit all of the section data in order.
+ for (std::list<ELFSection>::iterator I = SectionList.begin(),
+ E = SectionList.end(); I != E; ++I) {
+ // Align FileOff to whatever the alignment restrictions of the section are.
+ if (I->Align)
+ FileOff = (FileOff+I->Align-1) & ~(I->Align-1);
+ I->Offset = FileOff;
+ FileOff += I->SectionData.size();
+ }
+
+ // Align Section Header.
+ unsigned TableAlign = is64Bit ? 8 : 4;
+ FileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
+
+ // Now that we know where all of the sections will be emitted, set the e_shnum
+ // entry in the ELF header.
+ OutputBuffer FHOut(FileHeader, is64Bit, isLittleEndian);
+ FHOut.fixhalf(NumSections, ELFHeader_e_shnum_Offset);
+
+ // Now that we know the offset in the file of the section table, update the
+ // e_shoff address in the ELF header.
+ FHOut.fixaddr(FileOff, ELFHeader_e_shoff_Offset);
+
+ // Now that we know all of the data in the file header, emit it and all of the
+ // sections!
+ O.write((char*)&FileHeader[0], FileHeader.size());
+ FileOff = FileHeader.size();
+ DataBuffer().swap(FileHeader);
+
+ DataBuffer Table;
+ OutputBuffer TableOut(Table, is64Bit, isLittleEndian);
+
+ // Emit all of the section data and build the section table itself.
+ while (!SectionList.empty()) {
+ const ELFSection &S = *SectionList.begin();
+
+ // Align FileOff to whatever the alignment restrictions of the section are.
+ if (S.Align)
+ for (size_t NewFileOff = (FileOff+S.Align-1) & ~(S.Align-1);
+ FileOff != NewFileOff; ++FileOff)
+ O << (char)0xAB;
+ O.write((char*)&S.SectionData[0], S.SectionData.size());
+ FileOff += S.SectionData.size();
+
+ TableOut.outword(S.NameIdx); // sh_name - Symbol table name idx
+ TableOut.outword(S.Type); // sh_type - Section contents & semantics
+ TableOut.outword(S.Flags); // sh_flags - Section flags.
+ TableOut.outaddr(S.Addr); // sh_addr - The mem addr this section is in.
+ TableOut.outaddr(S.Offset); // sh_offset - Offset from the file start.
+ TableOut.outword(S.Size); // sh_size - The section size.
+ TableOut.outword(S.Link); // sh_link - Section header table index link.
+ TableOut.outword(S.Info); // sh_info - Auxillary information.
+ TableOut.outword(S.Align); // sh_addralign - Alignment of section.
+ TableOut.outword(S.EntSize); // sh_entsize - Size of entries in the section
+
+ SectionList.pop_front();
+ }
+
+ // Align output for the section table.
+ for (size_t NewFileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
+ FileOff != NewFileOff; ++FileOff)
+ O << (char)0xAB;
+
+ // Emit the section table itself.
+ O.write((char*)&Table[0], Table.size());
+}
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