X86TargetObjectFile.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338 
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#include "llvm/Target/TargetLowering.h"
18
19using namespace llvm;
20using namespace dwarf;
21
22const MCExpr *X86_64MachoTargetObjectFile::getTTypeGlobalReference(
23    const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
24    const TargetMachine &TM, MachineModuleInfo *MMI,
25    MCStreamer &Streamer) const {
26
27  // On Darwin/X86-64, we can reference dwarf symbols with foo@GOTPCREL+4, which
28  // is an indirect pc-relative reference.
29  if (Encoding & (DW_EH_PE_indirect | DW_EH_PE_pcrel)) {
30    const MCSymbol *Sym = TM.getSymbol(GV, Mang);
31    const MCExpr *Res =
32      MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_GOTPCREL, getContext());
33    const MCExpr *Four = MCConstantExpr::Create(4, getContext());
34    return MCBinaryExpr::CreateAdd(Res, Four, getContext());
35  }
36
37  return TargetLoweringObjectFileMachO::getTTypeGlobalReference(
38      GV, Encoding, Mang, TM, MMI, Streamer);
39}
40
41MCSymbol *X86_64MachoTargetObjectFile::getCFIPersonalitySymbol(
42    const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
43    MachineModuleInfo *MMI) const {
44  return TM.getSymbol(GV, Mang);
45}
46
47void
48X86LinuxTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM) {
49  TargetLoweringObjectFileELF::Initialize(Ctx, TM);
50  InitializeELF(TM.Options.UseInitArray);
51}
52
53const MCExpr *
54X86LinuxTargetObjectFile::getDebugThreadLocalSymbol(
55    const MCSymbol *Sym) const {
56  return MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_DTPOFF, getContext());
57}
58
59const MCExpr *X86WindowsTargetObjectFile::getExecutableRelativeSymbol(
60    const ConstantExpr *CE, Mangler &Mang, const TargetMachine &TM) const {
61  // We are looking for the difference of two symbols, need a subtraction
62  // operation.
63  const SubOperator *Sub = dyn_cast<SubOperator>(CE);
64  if (!Sub)
65    return 0;
66
67  // Symbols must first be numbers before we can subtract them, we need to see a
68  // ptrtoint on both subtraction operands.
69  const PtrToIntOperator *SubLHS =
70      dyn_cast<PtrToIntOperator>(Sub->getOperand(0));
71  const PtrToIntOperator *SubRHS =
72      dyn_cast<PtrToIntOperator>(Sub->getOperand(1));
73  if (!SubLHS || !SubRHS)
74    return 0;
75
76  // Our symbols should exist in address space zero, cowardly no-op if
77  // otherwise.
78  if (SubLHS->getPointerAddressSpace() != 0 ||
79      SubRHS->getPointerAddressSpace() != 0)
80    return 0;
81
82  // Both ptrtoint instructions must wrap global variables:
83  // - Only global variables are eligible for image relative relocations.
84  // - The subtrahend refers to the special symbol __ImageBase, a global.
85  const GlobalVariable *GVLHS =
86      dyn_cast<GlobalVariable>(SubLHS->getPointerOperand());
87  const GlobalVariable *GVRHS =
88      dyn_cast<GlobalVariable>(SubRHS->getPointerOperand());
89  if (!GVLHS || !GVRHS)
90    return 0;
91
92  // We expect __ImageBase to be a global variable without a section, externally
93  // defined.
94  //
95  // It should look something like this: @__ImageBase = external constant i8
96  if (GVRHS->isThreadLocal() || GVRHS->getName() != "__ImageBase" ||
97      !GVRHS->hasExternalLinkage() || GVRHS->hasInitializer() ||
98      GVRHS->hasSection())
99    return 0;
100
101  // An image-relative, thread-local, symbol makes no sense.
102  if (GVLHS->isThreadLocal())
103    return 0;
104
105  return MCSymbolRefExpr::Create(TM.getSymbol(GVLHS, Mang),
106                                 MCSymbolRefExpr::VK_COFF_IMGREL32,
107                                 getContext());
108}
109