1 //
2 // The LLVM Compiler Infrastructure
3 //
4 // This file is distributed under the University of Illinois Open Source
5 // License. See LICENSE.TXT for details.
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "LanaiTargetObjectFile.h"
10
11 #include "LanaiSubtarget.h"
12 #include "LanaiTargetMachine.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
22 using namespace llvm;
23
24 static cl::opt<unsigned> SSThreshold(
25 "lanai-ssection-threshold", cl::Hidden,
26 cl::desc("Small data and bss section threshold size (default=0)"),
27 cl::init(0));
28
Initialize(MCContext & Ctx,const TargetMachine & TM)29 void LanaiTargetObjectFile::Initialize(MCContext &Ctx,
30 const TargetMachine &TM) {
31 TargetLoweringObjectFileELF::Initialize(Ctx, TM);
32 InitializeELF(TM.Options.UseInitArray);
33
34 SmallDataSection = getContext().getELFSection(
35 ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
36 SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
37 ELF::SHF_WRITE | ELF::SHF_ALLOC);
38 }
39
40 // A address must be loaded from a small section if its size is less than the
41 // small section size threshold. Data in this section must be addressed using
42 // gp_rel operator.
isInSmallSection(uint64_t Size)43 static bool isInSmallSection(uint64_t Size) {
44 // gcc has traditionally not treated zero-sized objects as small data, so this
45 // is effectively part of the ABI.
46 return Size > 0 && Size <= SSThreshold;
47 }
48
49 // Return true if this global address should be placed into small data/bss
50 // section.
isGlobalInSmallSection(const GlobalValue * GV,const TargetMachine & TM) const51 bool LanaiTargetObjectFile::isGlobalInSmallSection(
52 const GlobalValue *GV, const TargetMachine &TM) const {
53 // We first check the case where global is a declaration, because finding
54 // section kind using getKindForGlobal() is only allowed for global
55 // definitions.
56 if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
57 return isGlobalInSmallSectionImpl(GV, TM);
58
59 return isGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
60 }
61
62 // Return true if this global address should be placed into small data/bss
63 // section.
isGlobalInSmallSection(const GlobalValue * GV,const TargetMachine & TM,SectionKind Kind) const64 bool LanaiTargetObjectFile::isGlobalInSmallSection(const GlobalValue *GV,
65 const TargetMachine &TM,
66 SectionKind Kind) const {
67 return (isGlobalInSmallSectionImpl(GV, TM) &&
68 (Kind.isData() || Kind.isBSS() || Kind.isCommon()));
69 }
70
71 // Return true if this global address should be placed into small data/bss
72 // section. This method does all the work, except for checking the section
73 // kind.
isGlobalInSmallSectionImpl(const GlobalValue * GV,const TargetMachine & TM) const74 bool LanaiTargetObjectFile::isGlobalInSmallSectionImpl(
75 const GlobalValue *GV, const TargetMachine &TM) const {
76 // Only global variables, not functions.
77 const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
78 if (!GVA)
79 return false;
80
81 if (GV->hasLocalLinkage())
82 return false;
83
84 if (((GV->hasExternalLinkage() && GV->isDeclaration()) ||
85 GV->hasCommonLinkage()))
86 return false;
87
88 Type *Ty = GV->getType()->getElementType();
89 return isInSmallSection(
90 GV->getParent()->getDataLayout().getTypeAllocSize(Ty));
91 }
92
93 MCSection *
SelectSectionForGlobal(const GlobalValue * GV,SectionKind Kind,Mangler & Mang,const TargetMachine & TM) const94 LanaiTargetObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
95 SectionKind Kind, Mangler &Mang,
96 const TargetMachine &TM) const {
97 // Handle Small Section classification here.
98 if (Kind.isBSS() && isGlobalInSmallSection(GV, TM, Kind))
99 return SmallBSSSection;
100 if (Kind.isData() && isGlobalInSmallSection(GV, TM, Kind))
101 return SmallDataSection;
102
103 // Otherwise, we work the same as ELF.
104 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,
105 TM);
106 }
107
108 /// Return true if this constant should be placed into small data section.
isConstantInSmallSection(const DataLayout & DL,const Constant * CN) const109 bool LanaiTargetObjectFile::isConstantInSmallSection(const DataLayout &DL,
110 const Constant *CN) const {
111 return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
112 }
113
getSectionForConstant(const DataLayout & DL,SectionKind Kind,const Constant * C,unsigned & Align) const114 MCSection *LanaiTargetObjectFile::getSectionForConstant(const DataLayout &DL,
115 SectionKind Kind,
116 const Constant *C,
117 unsigned &Align) const {
118 if (isConstantInSmallSection(DL, C))
119 return SmallDataSection;
120
121 // Otherwise, we work the same as ELF.
122 return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align);
123 }
124