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 "MipsTargetMachine.h"
13 #include "llvm/IR/DataLayout.h"
14 #include "llvm/IR/DerivedTypes.h"
15 #include "llvm/IR/GlobalVariable.h"
16 #include "llvm/MC/MCContext.h"
17 #include "llvm/MC/MCSectionELF.h"
18 #include "llvm/Support/CommandLine.h"
19 #include "llvm/Support/ELF.h"
20 #include "llvm/Target/TargetMachine.h"
21 using namespace llvm;
22 
23 static cl::opt<unsigned>
24 SSThreshold("mips-ssection-threshold", cl::Hidden,
25             cl::desc("Small data and bss section threshold size (default=8)"),
26             cl::init(8));
27 
28 static cl::opt<bool>
29 LocalSData("mlocal-sdata", cl::Hidden,
30            cl::desc("MIPS: Use gp_rel for object-local data."),
31            cl::init(true));
32 
33 static cl::opt<bool>
34 ExternSData("mextern-sdata", cl::Hidden,
35             cl::desc("MIPS: Use gp_rel for data that is not defined by the "
36                      "current object."),
37             cl::init(true));
38 
Initialize(MCContext & Ctx,const TargetMachine & TM)39 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
40   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
41   InitializeELF(TM.Options.UseInitArray);
42 
43   SmallDataSection = getContext().getELFSection(
44       ".sdata", ELF::SHT_PROGBITS,
45       ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_MIPS_GPREL);
46 
47   SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
48                                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
49                                                    ELF::SHF_MIPS_GPREL);
50   this->TM = &static_cast<const MipsTargetMachine &>(TM);
51 }
52 
53 // A address must be loaded from a small section if its size is less than the
54 // small section size threshold. Data in this section must be addressed using
55 // gp_rel operator.
IsInSmallSection(uint64_t Size)56 static bool IsInSmallSection(uint64_t Size) {
57   // gcc has traditionally not treated zero-sized objects as small data, so this
58   // is effectively part of the ABI.
59   return Size > 0 && Size <= SSThreshold;
60 }
61 
62 /// Return true if this global address should be placed into small data/bss
63 /// section.
64 bool MipsTargetObjectFile::
IsGlobalInSmallSection(const GlobalValue * GV,const TargetMachine & TM) const65 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM) const {
66   // We first check the case where global is a declaration, because finding
67   // section kind using getKindForGlobal() is only allowed for global
68   // definitions.
69   if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
70     return IsGlobalInSmallSectionImpl(GV, TM);
71 
72   return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
73 }
74 
75 /// Return true if this global address should be placed into small data/bss
76 /// section.
77 bool MipsTargetObjectFile::
IsGlobalInSmallSection(const GlobalValue * GV,const TargetMachine & TM,SectionKind Kind) const78 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
79                        SectionKind Kind) const {
80   return (IsGlobalInSmallSectionImpl(GV, TM) &&
81           (Kind.isData() || Kind.isBSS() || Kind.isCommon()));
82 }
83 
84 /// Return true if this global address should be placed into small data/bss
85 /// section. This method does all the work, except for checking the section
86 /// kind.
87 bool MipsTargetObjectFile::
IsGlobalInSmallSectionImpl(const GlobalValue * GV,const TargetMachine & TM) const88 IsGlobalInSmallSectionImpl(const GlobalValue *GV,
89                            const TargetMachine &TM) const {
90   const MipsSubtarget &Subtarget =
91       *static_cast<const MipsTargetMachine &>(TM).getSubtargetImpl();
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->getValueType();
112   return IsInSmallSection(
113       GV->getParent()->getDataLayout().getTypeAllocSize(Ty));
114 }
115 
116 MCSection *
SelectSectionForGlobal(const GlobalValue * GV,SectionKind Kind,Mangler & Mang,const TargetMachine & TM) const117 MipsTargetObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
118                                              SectionKind Kind, Mangler &Mang,
119                                              const TargetMachine &TM) const {
120   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
121   // sections?
122 
123   // Handle Small Section classification here.
124   if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
125     return SmallBSSSection;
126   if (Kind.isData() && IsGlobalInSmallSection(GV, TM, Kind))
127     return SmallDataSection;
128 
129   // Otherwise, we work the same as ELF.
130   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
131 }
132 
133 /// Return true if this constant should be placed into small data section.
IsConstantInSmallSection(const DataLayout & DL,const Constant * CN,const TargetMachine & TM) const134 bool MipsTargetObjectFile::IsConstantInSmallSection(
135     const DataLayout &DL, const Constant *CN, const TargetMachine &TM) const {
136   return (static_cast<const MipsTargetMachine &>(TM)
137               .getSubtargetImpl()
138               ->useSmallSection() &&
139           LocalSData && IsInSmallSection(DL.getTypeAllocSize(CN->getType())));
140 }
141 
142 /// Return true if this constant should be placed into small data section.
getSectionForConstant(const DataLayout & DL,SectionKind Kind,const Constant * C,unsigned & Align) const143 MCSection *MipsTargetObjectFile::getSectionForConstant(const DataLayout &DL,
144                                                        SectionKind Kind,
145                                                        const Constant *C,
146                                                        unsigned &Align) const {
147   if (IsConstantInSmallSection(DL, C, *TM))
148     return SmallDataSection;
149 
150   // Otherwise, we work the same as ELF.
151   return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align);
152 }
153