1 //===-- MipsTargetObjectFile.cpp - Mips Object Files ----------------------===//
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 "MipsTargetObjectFile.h"
11 #include "MipsSubtarget.h"
12 #include "llvm/IR/DataLayout.h"
13 #include "llvm/IR/DerivedTypes.h"
14 #include "llvm/IR/GlobalVariable.h"
15 #include "llvm/MC/MCContext.h"
16 #include "llvm/MC/MCSectionELF.h"
17 #include "llvm/Support/CommandLine.h"
18 #include "llvm/Support/ELF.h"
19 #include "llvm/Target/TargetMachine.h"
20 using namespace llvm;
21
22 static cl::opt<unsigned>
23 SSThreshold("mips-ssection-threshold", cl::Hidden,
24 cl::desc("Small data and bss section threshold size (default=8)"),
25 cl::init(8));
26
27 static cl::opt<bool>
28 LocalSData("mlocal-sdata", cl::Hidden,
29 cl::desc("MIPS: Use gp_rel for object-local data."),
30 cl::init(true));
31
32 static cl::opt<bool>
33 ExternSData("mextern-sdata", cl::Hidden,
34 cl::desc("MIPS: Use gp_rel for data that is not defined by the "
35 "current object."),
36 cl::init(true));
37
Initialize(MCContext & Ctx,const TargetMachine & TM)38 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
39 TargetLoweringObjectFileELF::Initialize(Ctx, TM);
40 InitializeELF(TM.Options.UseInitArray);
41
42 SmallDataSection =
43 getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
44 ELF::SHF_WRITE |ELF::SHF_ALLOC,
45 SectionKind::getDataRel());
46
47 SmallBSSSection =
48 getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
49 ELF::SHF_WRITE |ELF::SHF_ALLOC,
50 SectionKind::getBSS());
51 this->TM = &TM;
52 }
53
54 // A address must be loaded from a small section if its size is less than the
55 // small section size threshold. Data in this section must be addressed using
56 // gp_rel operator.
IsInSmallSection(uint64_t Size)57 static bool IsInSmallSection(uint64_t Size) {
58 // gcc has traditionally not treated zero-sized objects as small data, so this
59 // is effectively part of the ABI.
60 return Size > 0 && Size <= SSThreshold;
61 }
62
63 /// Return true if this global address should be placed into small data/bss
64 /// section.
65 bool MipsTargetObjectFile::
IsGlobalInSmallSection(const GlobalValue * GV,const TargetMachine & TM) const66 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM) const {
67 // We first check the case where global is a declaration, because finding
68 // section kind using getKindForGlobal() is only allowed for global
69 // definitions.
70 if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
71 return IsGlobalInSmallSectionImpl(GV, TM);
72
73 return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
74 }
75
76 /// Return true if this global address should be placed into small data/bss
77 /// section.
78 bool MipsTargetObjectFile::
IsGlobalInSmallSection(const GlobalValue * GV,const TargetMachine & TM,SectionKind Kind) const79 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
80 SectionKind Kind) const {
81 return (IsGlobalInSmallSectionImpl(GV, TM) &&
82 (Kind.isDataRel() || Kind.isBSS() || Kind.isCommon()));
83 }
84
85 /// Return true if this global address should be placed into small data/bss
86 /// section. This method does all the work, except for checking the section
87 /// kind.
88 bool MipsTargetObjectFile::
IsGlobalInSmallSectionImpl(const GlobalValue * GV,const TargetMachine & TM) const89 IsGlobalInSmallSectionImpl(const GlobalValue *GV,
90 const TargetMachine &TM) const {
91 const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
92
93 // Return if small section is not available.
94 if (!Subtarget.useSmallSection())
95 return false;
96
97 // Only global variables, not functions.
98 const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
99 if (!GVA)
100 return false;
101
102 // Enforce -mlocal-sdata.
103 if (!LocalSData && GV->hasLocalLinkage())
104 return false;
105
106 // Enforce -mextern-sdata.
107 if (!ExternSData && ((GV->hasExternalLinkage() && GV->isDeclaration()) ||
108 GV->hasCommonLinkage()))
109 return false;
110
111 Type *Ty = GV->getType()->getElementType();
112 return IsInSmallSection(
113 TM.getSubtargetImpl()->getDataLayout()->getTypeAllocSize(Ty));
114 }
115
116 const MCSection *MipsTargetObjectFile::
SelectSectionForGlobal(const GlobalValue * GV,SectionKind Kind,Mangler & Mang,const TargetMachine & TM) const117 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
118 Mangler &Mang, const TargetMachine &TM) const {
119 // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
120 // sections?
121
122 // Handle Small Section classification here.
123 if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
124 return SmallBSSSection;
125 if (Kind.isDataRel() && IsGlobalInSmallSection(GV, TM, Kind))
126 return SmallDataSection;
127
128 // Otherwise, we work the same as ELF.
129 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
130 }
131
132 /// Return true if this constant should be placed into small data section.
133 bool MipsTargetObjectFile::
IsConstantInSmallSection(const Constant * CN,const TargetMachine & TM) const134 IsConstantInSmallSection(const Constant *CN, const TargetMachine &TM) const {
135 return (TM.getSubtarget<MipsSubtarget>().useSmallSection() &&
136 LocalSData &&
137 IsInSmallSection(TM.getSubtargetImpl()->getDataLayout()
138 ->getTypeAllocSize(CN->getType())));
139 }
140
141 const MCSection *MipsTargetObjectFile::
getSectionForConstant(SectionKind Kind,const Constant * C) const142 getSectionForConstant(SectionKind Kind, const Constant *C) const {
143 if (IsConstantInSmallSection(C, *TM))
144 return SmallDataSection;
145
146 // Otherwise, we work the same as ELF.
147 return TargetLoweringObjectFileELF::getSectionForConstant(Kind, C);
148 }
149