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/BinaryFormat/ELF.h"
14 #include "llvm/IR/DataLayout.h"
15 #include "llvm/IR/DerivedTypes.h"
16 #include "llvm/IR/GlobalVariable.h"
17 #include "llvm/MC/MCContext.h"
18 #include "llvm/MC/MCSectionELF.h"
19 #include "llvm/Support/CommandLine.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 
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.
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.
51 bool LanaiTargetObjectFile::isGlobalInSmallSection(
52     const GlobalObject *GO, const TargetMachine &TM) const {
53   if (GO == nullptr)
54     return false;
55 
56   // We first check the case where global is a declaration, because finding
57   // section kind using getKindForGlobal() is only allowed for global
58   // definitions.
59   if (GO->isDeclaration() || GO->hasAvailableExternallyLinkage())
60     return isGlobalInSmallSectionImpl(GO, TM);
61 
62   return isGlobalInSmallSection(GO, TM, getKindForGlobal(GO, TM));
63 }
64 
65 // Return true if this global address should be placed into small data/bss
66 // section.
67 bool LanaiTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
68                                                    const TargetMachine &TM,
69                                                    SectionKind Kind) const {
70   return (isGlobalInSmallSectionImpl(GO, TM) &&
71           (Kind.isData() || Kind.isBSS() || Kind.isCommon()));
72 }
73 
74 // Return true if this global address should be placed into small data/bss
75 // section. This method does all the work, except for checking the section
76 // kind.
77 bool LanaiTargetObjectFile::isGlobalInSmallSectionImpl(
78     const GlobalObject *GO, const TargetMachine &TM) const {
79   // Only global variables, not functions.
80   const auto *GVA = dyn_cast<GlobalVariable>(GO);
81   if (!GVA)
82     return false;
83 
84   // Global values placed in sections starting with .ldata do not fit in
85   // 21-bits, so always use large memory access for them. FIXME: This is a
86   // workaround for a tool limitation.
87   if (GVA->getSection().startswith(".ldata"))
88     return false;
89 
90   if (TM.getCodeModel() == CodeModel::Small)
91     return true;
92 
93   if (GVA->hasLocalLinkage())
94     return false;
95 
96   if (((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||
97        GVA->hasCommonLinkage()))
98     return false;
99 
100   Type *Ty = GVA->getValueType();
101   return isInSmallSection(
102       GVA->getParent()->getDataLayout().getTypeAllocSize(Ty));
103 }
104 
105 MCSection *LanaiTargetObjectFile::SelectSectionForGlobal(
106     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
107   // Handle Small Section classification here.
108   if (Kind.isBSS() && isGlobalInSmallSection(GO, TM, Kind))
109     return SmallBSSSection;
110   if (Kind.isData() && isGlobalInSmallSection(GO, TM, Kind))
111     return SmallDataSection;
112 
113   // Otherwise, we work the same as ELF.
114   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
115 }
116 
117 /// Return true if this constant should be placed into small data section.
118 bool LanaiTargetObjectFile::isConstantInSmallSection(const DataLayout &DL,
119                                                      const Constant *CN) const {
120   return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
121 }
122 
123 MCSection *LanaiTargetObjectFile::getSectionForConstant(const DataLayout &DL,
124                                                         SectionKind Kind,
125                                                         const Constant *C,
126                                                         unsigned &Align) const {
127   if (isConstantInSmallSection(DL, C))
128     return SmallDataSection;
129 
130   // Otherwise, we work the same as ELF.
131   return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align);
132 }
133