1 //===-- lib/CodeGen/ELFCodeEmitter.cpp ------------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #define DEBUG_TYPE "elfce"
13 #include "ELFWriter.h"
14 #include "ELFCodeEmitter.h"
15 #include "llvm/Constants.h"
16 #include "llvm/DerivedTypes.h"
17 #include "llvm/Function.h"
18 #include "llvm/CodeGen/BinaryObject.h"
19 #include "llvm/CodeGen/MachineConstantPool.h"
20 #include "llvm/CodeGen/MachineJumpTableInfo.h"
21 #include "llvm/CodeGen/MachineRelocation.h"
22 #include "llvm/Target/TargetData.h"
23 #include "llvm/Target/TargetMachine.h"
24 #include "llvm/Target/TargetAsmInfo.h"
25 #include "llvm/Support/Debug.h"
27 //===----------------------------------------------------------------------===//
28 // ELFCodeEmitter Implementation
29 //===----------------------------------------------------------------------===//
33 /// startFunction - This callback is invoked when a new machine function is
34 /// about to be emitted.
35 void ELFCodeEmitter::startFunction(MachineFunction &MF) {
36 // Get the ELF Section that this function belongs in.
37 ES = &EW.getTextSection();
39 DOUT << "processing function: " << MF.getFunction()->getName() << "\n";
41 // FIXME: better memory management, this will be replaced by BinaryObjects
42 BinaryData &BD = ES->getData();
45 BufferEnd = BufferBegin + BD.capacity();
47 // Get the function alignment in bytes
48 unsigned Align = (1 << MF.getAlignment());
50 // Align the section size with the function alignment, so the function can
51 // start in a aligned offset, also update the section alignment if needed.
52 if (ES->Align < Align) ES->Align = Align;
53 ES->Size = (ES->Size + (Align-1)) & (-Align);
55 // Snaity check on allocated space for text section
56 assert( ES->Size < 4096 && "no more space in TextSection" );
58 // FIXME: Using ES->Size directly here instead of calculating it from the
59 // output buffer size (impossible because the code emitter deals only in raw
60 // bytes) forces us to manually synchronize size and write padding zero bytes
61 // to the output buffer for all non-text sections. For text sections, we do
62 // not synchonize the output buffer, and we just blow up if anyone tries to
63 // write non-code to it. An assert should probably be added to
64 // AddSymbolToSection to prevent calling it on the text section.
65 CurBufferPtr = BufferBegin + ES->Size;
67 // Record function start address relative to BufferBegin
68 FnStartPtr = CurBufferPtr;
71 /// finishFunction - This callback is invoked after the function is completely
73 bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
74 // Update Section Size
75 ES->Size = CurBufferPtr - BufferBegin;
77 // Add a symbol to represent the function.
78 const Function *F = MF.getFunction();
80 FnSym.setType(ELFSym::STT_FUNC);
81 FnSym.setBind(EW.getGlobalELFLinkage(F));
82 FnSym.setVisibility(EW.getGlobalELFVisibility(F));
83 FnSym.SectionIdx = ES->SectionIdx;
84 FnSym.Size = CurBufferPtr-FnStartPtr;
86 // Offset from start of Section
87 FnSym.Value = FnStartPtr-BufferBegin;
89 // Locals should go on the symbol list front
90 if (!F->hasPrivateLinkage()) {
91 if (FnSym.getBind() == ELFSym::STB_LOCAL)
92 EW.SymbolList.push_front(FnSym);
94 EW.SymbolList.push_back(FnSym);
97 // Emit constant pool to appropriate section(s)
98 emitConstantPool(MF.getConstantPool());
100 // Emit jump tables to appropriate section
101 emitJumpTables(MF.getJumpTableInfo());
105 // If we have emitted any relocations to function-specific objects such as
106 // basic blocks, constant pools entries, or jump tables, record their
107 // addresses now so that we can rewrite them with the correct addresses
109 for (unsigned i = 0, e = Relocations.size(); i != e; ++i) {
110 MachineRelocation &MR = Relocations[i];
112 if (MR.isGlobalValue()) {
113 EW.PendingGlobals.insert(MR.getGlobalValue());
114 } else if (MR.isBasicBlock()) {
115 Addr = getMachineBasicBlockAddress(MR.getBasicBlock());
116 MR.setConstantVal(ES->SectionIdx);
117 MR.setResultPointer((void*)Addr);
118 } else if (MR.isConstantPoolIndex()) {
119 Addr = getConstantPoolEntryAddress(MR.getConstantPoolIndex());
120 MR.setConstantVal(CPSections[MR.getConstantPoolIndex()]);
121 MR.setResultPointer((void*)Addr);
122 } else if (MR.isJumpTableIndex()) {
123 Addr = getJumpTableEntryAddress(MR.getJumpTableIndex());
124 MR.setResultPointer((void*)Addr);
125 MR.setConstantVal(JumpTableSectionIdx);
127 assert(0 && "Unhandled relocation type");
129 ES->addRelocation(MR);
132 // Clear per-function data structures.
137 MBBLocations.clear();
141 /// emitConstantPool - For each constant pool entry, figure out which section
142 /// the constant should live in and emit the constant
143 void ELFCodeEmitter::emitConstantPool(MachineConstantPool *MCP) {
144 const std::vector<MachineConstantPoolEntry> &CP = MCP->getConstants();
145 if (CP.empty()) return;
147 // TODO: handle PIC codegen
148 assert(TM.getRelocationModel() != Reloc::PIC_ &&
149 "PIC codegen not yet handled for elf constant pools!");
151 const TargetAsmInfo *TAI = TM.getTargetAsmInfo();
152 for (unsigned i = 0, e = CP.size(); i != e; ++i) {
153 MachineConstantPoolEntry CPE = CP[i];
155 // Get the right ELF Section for this constant pool entry
156 std::string CstPoolName =
157 TAI->SelectSectionForMachineConst(CPE.getType())->getName();
158 ELFSection &CstPoolSection =
159 EW.getConstantPoolSection(CstPoolName, CPE.getAlignment());
161 // Record the constant pool location and the section index
162 CPLocations.push_back(CstPoolSection.size());
163 CPSections.push_back(CstPoolSection.SectionIdx);
165 if (CPE.isMachineConstantPoolEntry())
166 assert("CPE.isMachineConstantPoolEntry not supported yet");
168 // Emit the constant to constant pool section
169 EW.EmitGlobalConstant(CPE.Val.ConstVal, CstPoolSection);
173 /// emitJumpTables - Emit all the jump tables for a given jump table info
174 /// record to the appropriate section.
175 void ELFCodeEmitter::emitJumpTables(MachineJumpTableInfo *MJTI) {
176 const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
177 if (JT.empty()) return;
179 // FIXME: handle PIC codegen
180 assert(TM.getRelocationModel() != Reloc::PIC_ &&
181 "PIC codegen not yet handled for elf jump tables!");
183 const TargetAsmInfo *TAI = TM.getTargetAsmInfo();
185 // Get the ELF Section to emit the jump table
186 unsigned Align = TM.getTargetData()->getPointerABIAlignment();
187 std::string JTName(TAI->getJumpTableDataSection());
188 ELFSection &JTSection = EW.getJumpTableSection(JTName, Align);
189 JumpTableSectionIdx = JTSection.SectionIdx;
191 // Entries in the JT Section are relocated against the text section
192 ELFSection &TextSection = EW.getTextSection();
194 // For each JT, record its offset from the start of the section
195 for (unsigned i = 0, e = JT.size(); i != e; ++i) {
196 const std::vector<MachineBasicBlock*> &MBBs = JT[i].MBBs;
198 DOUT << "JTSection.size(): " << JTSection.size() << "\n";
199 DOUT << "JTLocations.size: " << JTLocations.size() << "\n";
201 // Record JT 'i' offset in the JT section
202 JTLocations.push_back(JTSection.size());
204 // Each MBB entry in the Jump table section has a relocation entry
205 // against the current text section.
206 for (unsigned mi = 0, me = MBBs.size(); mi != me; ++mi) {
207 MachineRelocation MR =
208 MachineRelocation::getBB(JTSection.size(),
209 MachineRelocation::VANILLA,
212 // Offset of JT 'i' in JT section
213 MR.setResultPointer((void*)getMachineBasicBlockAddress(MBBs[mi]));
214 MR.setConstantVal(TextSection.SectionIdx);
216 // Add the relocation to the Jump Table section
217 JTSection.addRelocation(MR);
219 // Output placeholder for MBB in the JT section
220 JTSection.emitWord(0);
225 } // end namespace llvm