1 //===-- X86TargetObjectFile.cpp - X86 Object Info -------------------------===//
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 #include "X86TargetObjectFile.h"
11 #include "llvm/IR/Mangler.h"
12 #include "llvm/IR/Operator.h"
13 #include "llvm/MC/MCContext.h"
14 #include "llvm/MC/MCExpr.h"
15 #include "llvm/MC/MCSectionELF.h"
16 #include "llvm/Support/Dwarf.h"
17 
18 using namespace llvm;
19 using namespace dwarf;
20 
21 const MCExpr *X86_64MachoTargetObjectFile::getTTypeGlobalReference(
22     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
23     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
24 
25   // On Darwin/X86-64, we can reference dwarf symbols with foo@GOTPCREL+4, which
26   // is an indirect pc-relative reference.
27   if (Encoding & (DW_EH_PE_indirect | DW_EH_PE_pcrel)) {
28     const MCSymbol *Sym = getSymbol(GV, Mang);
29     const MCExpr *Res =
30       MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_GOTPCREL, getContext());
31     const MCExpr *Four = MCConstantExpr::Create(4, getContext());
32     return MCBinaryExpr::CreateAdd(Res, Four, getContext());
33   }
34 
35   return TargetLoweringObjectFileMachO::getTTypeGlobalReference(
36       GV, Encoding, Mang, MMI, Streamer);
37 }
38 
39 MCSymbol *X86_64MachoTargetObjectFile::
40 getCFIPersonalitySymbol(const GlobalValue *GV, Mangler &Mang,
41                         MachineModuleInfo *MMI) const {
42   return getSymbol(GV, Mang);
43 }
44 
45 void
46 X86LinuxTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM) {
47   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
48   InitializeELF(TM.Options.UseInitArray);
49 }
50 
51 const MCExpr *
52 X86LinuxTargetObjectFile::getDebugThreadLocalSymbol(
53     const MCSymbol *Sym) const {
54   return MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_DTPOFF, getContext());
55 }
56 
57 const MCExpr *
58 X86WindowsTargetObjectFile::getExecutableRelativeSymbol(const ConstantExpr *CE,
59                                                         Mangler &Mang) const {
60   // We are looking for the difference of two symbols, need a subtraction
61   // operation.
62   const SubOperator *Sub = dyn_cast<SubOperator>(CE);
63   if (!Sub)
64     return 0;
65 
66   // Symbols must first be numbers before we can subtract them, we need to see a
67   // ptrtoint on both subtraction operands.
68   const PtrToIntOperator *SubLHS =
69       dyn_cast<PtrToIntOperator>(Sub->getOperand(0));
70   const PtrToIntOperator *SubRHS =
71       dyn_cast<PtrToIntOperator>(Sub->getOperand(1));
72   if (!SubLHS || !SubRHS)
73     return 0;
74 
75   // Our symbols should exist in address space zero, cowardly no-op if
76   // otherwise.
77   if (SubLHS->getPointerAddressSpace() != 0 ||
78       SubRHS->getPointerAddressSpace() != 0)
79     return 0;
80 
81   // Both ptrtoint instructions must wrap global variables:
82   // - Only global variables are eligible for image relative relocations.
83   // - The subtrahend refers to the special symbol __ImageBase, a global.
84   const GlobalVariable *GVLHS =
85       dyn_cast<GlobalVariable>(SubLHS->getPointerOperand());
86   const GlobalVariable *GVRHS =
87       dyn_cast<GlobalVariable>(SubRHS->getPointerOperand());
88   if (!GVLHS || !GVRHS)
89     return 0;
90 
91   // We expect __ImageBase to be a global variable without a section, externally
92   // defined.
93   //
94   // It should look something like this: @__ImageBase = external constant i8
95   if (GVRHS->isThreadLocal() || GVRHS->getName() != "__ImageBase" ||
96       !GVRHS->hasExternalLinkage() || GVRHS->hasInitializer() ||
97       GVRHS->hasSection())
98     return 0;
99 
100   // An image-relative, thread-local, symbol makes no sense.
101   if (GVLHS->isThreadLocal())
102     return 0;
103 
104   return MCSymbolRefExpr::Create(
105       getSymbol(GVLHS, Mang), MCSymbolRefExpr::VK_COFF_IMGREL32, getContext());
106 }
107