1 //===-- lib/CodeGen/ELFCodeEmitter.cpp ------------------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9
10 #define DEBUG_TYPE "elfce"
11
12 #include "ELF.h"
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/MachineFunction.h"
21 #include "llvm/CodeGen/MachineJumpTableInfo.h"
22 #include "llvm/CodeGen/MachineRelocation.h"
23 #include "llvm/Target/TargetData.h"
24 #include "llvm/Target/TargetELFWriterInfo.h"
25 #include "llvm/Target/TargetMachine.h"
26 #include "llvm/MC/MCAsmInfo.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Support/raw_ostream.h"
30
31 //===----------------------------------------------------------------------===//
32 // ELFCodeEmitter Implementation
33 //===----------------------------------------------------------------------===//
34
35 namespace llvm {
36
37 /// startFunction - This callback is invoked when a new machine function is
38 /// about to be emitted.
startFunction(MachineFunction & MF)39 void ELFCodeEmitter::startFunction(MachineFunction &MF) {
40 DEBUG(dbgs() << "processing function: "
41 << MF.getFunction()->getName() << "\n");
42
43 // Get the ELF Section that this function belongs in.
44 ES = &EW.getTextSection(MF.getFunction());
45
46 // Set the desired binary object to be used by the code emitters
47 setBinaryObject(ES);
48
49 // Get the function alignment in bytes
50 unsigned Align = (1 << MF.getAlignment());
51
52 // The function must start on its required alignment
53 ES->emitAlignment(Align);
54
55 // Update the section alignment if needed.
56 ES->Align = std::max(ES->Align, Align);
57
58 // Record the function start offset
59 FnStartOff = ES->getCurrentPCOffset();
60
61 // Emit constant pool and jump tables to their appropriate sections.
62 // They need to be emitted before the function because in some targets
63 // the later may reference JT or CP entry address.
64 emitConstantPool(MF.getConstantPool());
65 if (MF.getJumpTableInfo())
66 emitJumpTables(MF.getJumpTableInfo());
67 }
68
69 /// finishFunction - This callback is invoked after the function is completely
70 /// finished.
finishFunction(MachineFunction & MF)71 bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
72 // Add a symbol to represent the function.
73 const Function *F = MF.getFunction();
74 ELFSym *FnSym = ELFSym::getGV(F, EW.getGlobalELFBinding(F), ELF::STT_FUNC,
75 EW.getGlobalELFVisibility(F));
76 FnSym->SectionIdx = ES->SectionIdx;
77 FnSym->Size = ES->getCurrentPCOffset()-FnStartOff;
78 EW.AddPendingGlobalSymbol(F, true);
79
80 // Offset from start of Section
81 FnSym->Value = FnStartOff;
82
83 if (!F->hasPrivateLinkage())
84 EW.SymbolList.push_back(FnSym);
85
86 // Patch up Jump Table Section relocations to use the real MBBs offsets
87 // now that the MBB label offsets inside the function are known.
88 if (MF.getJumpTableInfo()) {
89 ELFSection &JTSection = EW.getJumpTableSection();
90 for (std::vector<MachineRelocation>::iterator MRI = JTRelocations.begin(),
91 MRE = JTRelocations.end(); MRI != MRE; ++MRI) {
92 MachineRelocation &MR = *MRI;
93 uintptr_t MBBOffset = getMachineBasicBlockAddress(MR.getBasicBlock());
94 MR.setResultPointer((void*)MBBOffset);
95 MR.setConstantVal(ES->SectionIdx);
96 JTSection.addRelocation(MR);
97 }
98 }
99
100 // If we have emitted any relocations to function-specific objects such as
101 // basic blocks, constant pools entries, or jump tables, record their
102 // addresses now so that we can rewrite them with the correct addresses later
103 for (unsigned i = 0, e = Relocations.size(); i != e; ++i) {
104 MachineRelocation &MR = Relocations[i];
105 intptr_t Addr;
106 if (MR.isGlobalValue()) {
107 EW.AddPendingGlobalSymbol(MR.getGlobalValue());
108 } else if (MR.isExternalSymbol()) {
109 EW.AddPendingExternalSymbol(MR.getExternalSymbol());
110 } else if (MR.isBasicBlock()) {
111 Addr = getMachineBasicBlockAddress(MR.getBasicBlock());
112 MR.setConstantVal(ES->SectionIdx);
113 MR.setResultPointer((void*)Addr);
114 } else if (MR.isConstantPoolIndex()) {
115 Addr = getConstantPoolEntryAddress(MR.getConstantPoolIndex());
116 MR.setConstantVal(CPSections[MR.getConstantPoolIndex()]);
117 MR.setResultPointer((void*)Addr);
118 } else if (MR.isJumpTableIndex()) {
119 ELFSection &JTSection = EW.getJumpTableSection();
120 Addr = getJumpTableEntryAddress(MR.getJumpTableIndex());
121 MR.setConstantVal(JTSection.SectionIdx);
122 MR.setResultPointer((void*)Addr);
123 } else {
124 llvm_unreachable("Unhandled relocation type");
125 }
126 ES->addRelocation(MR);
127 }
128
129 // Clear per-function data structures.
130 JTRelocations.clear();
131 Relocations.clear();
132 CPLocations.clear();
133 CPSections.clear();
134 JTLocations.clear();
135 MBBLocations.clear();
136 return false;
137 }
138
139 /// emitConstantPool - For each constant pool entry, figure out which section
140 /// the constant should live in and emit the constant
emitConstantPool(MachineConstantPool * MCP)141 void ELFCodeEmitter::emitConstantPool(MachineConstantPool *MCP) {
142 const std::vector<MachineConstantPoolEntry> &CP = MCP->getConstants();
143 if (CP.empty()) return;
144
145 // TODO: handle PIC codegen
146 assert(TM.getRelocationModel() != Reloc::PIC_ &&
147 "PIC codegen not yet handled for elf constant pools!");
148
149 for (unsigned i = 0, e = CP.size(); i != e; ++i) {
150 MachineConstantPoolEntry CPE = CP[i];
151
152 // Record the constant pool location and the section index
153 ELFSection &CstPool = EW.getConstantPoolSection(CPE);
154 CPLocations.push_back(CstPool.size());
155 CPSections.push_back(CstPool.SectionIdx);
156
157 if (CPE.isMachineConstantPoolEntry())
158 assert(0 && "CPE.isMachineConstantPoolEntry not supported yet");
159
160 // Emit the constant to constant pool section
161 EW.EmitGlobalConstant(CPE.Val.ConstVal, CstPool);
162 }
163 }
164
165 /// emitJumpTables - Emit all the jump tables for a given jump table info
166 /// record to the appropriate section.
emitJumpTables(MachineJumpTableInfo * MJTI)167 void ELFCodeEmitter::emitJumpTables(MachineJumpTableInfo *MJTI) {
168 const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
169 if (JT.empty()) return;
170
171 // FIXME: handle PIC codegen
172 assert(TM.getRelocationModel() != Reloc::PIC_ &&
173 "PIC codegen not yet handled for elf jump tables!");
174
175 const TargetELFWriterInfo *TEW = TM.getELFWriterInfo();
176 unsigned EntrySize = 4; //MJTI->getEntrySize();
177
178 // Get the ELF Section to emit the jump table
179 ELFSection &JTSection = EW.getJumpTableSection();
180
181 // For each JT, record its offset from the start of the section
182 for (unsigned i = 0, e = JT.size(); i != e; ++i) {
183 const std::vector<MachineBasicBlock*> &MBBs = JT[i].MBBs;
184
185 // Record JT 'i' offset in the JT section
186 JTLocations.push_back(JTSection.size());
187
188 // Each MBB entry in the Jump table section has a relocation entry
189 // against the current text section.
190 for (unsigned mi = 0, me = MBBs.size(); mi != me; ++mi) {
191 unsigned MachineRelTy = TEW->getAbsoluteLabelMachineRelTy();
192 MachineRelocation MR =
193 MachineRelocation::getBB(JTSection.size(), MachineRelTy, MBBs[mi]);
194
195 // Add the relocation to the Jump Table section
196 JTRelocations.push_back(MR);
197
198 // Output placeholder for MBB in the JT section
199 for (unsigned s=0; s < EntrySize; ++s)
200 JTSection.emitByte(0);
201 }
202 }
203 }
204
205 } // end namespace llvm
206