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