1 //
2 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
3 // See https://llvm.org/LICENSE.txt for license information.
4 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
5 //
6 //===----------------------------------------------------------------------===//
7
8 #include "LanaiTargetObjectFile.h"
9
10 #include "LanaiSubtarget.h"
11 #include "LanaiTargetMachine.h"
12 #include "llvm/BinaryFormat/ELF.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/Target/TargetMachine.h"
20
21 using namespace llvm;
22
23 static cl::opt<unsigned> SSThreshold(
24 "lanai-ssection-threshold", cl::Hidden,
25 cl::desc("Small data and bss section threshold size (default=0)"),
26 cl::init(0));
27
Initialize(MCContext & Ctx,const TargetMachine & TM)28 void LanaiTargetObjectFile::Initialize(MCContext &Ctx,
29 const TargetMachine &TM) {
30 TargetLoweringObjectFileELF::Initialize(Ctx, TM);
31
32 SmallDataSection = getContext().getELFSection(
33 ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
34 SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
35 ELF::SHF_WRITE | ELF::SHF_ALLOC);
36 }
37
38 // A address must be loaded from a small section if its size is less than the
39 // small section size threshold. Data in this section must be addressed using
40 // gp_rel operator.
isInSmallSection(uint64_t Size)41 static bool isInSmallSection(uint64_t Size) {
42 // gcc has traditionally not treated zero-sized objects as small data, so this
43 // is effectively part of the ABI.
44 return Size > 0 && Size <= SSThreshold;
45 }
46
47 // Return true if this global address should be placed into small data/bss
48 // section.
isGlobalInSmallSection(const GlobalObject * GO,const TargetMachine & TM) const49 bool LanaiTargetObjectFile::isGlobalInSmallSection(
50 const GlobalObject *GO, const TargetMachine &TM) const {
51 if (GO == nullptr) return TM.getCodeModel() == CodeModel::Small;
52
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 (GO->isDeclaration() || GO->hasAvailableExternallyLinkage())
57 return isGlobalInSmallSectionImpl(GO, TM);
58
59 return isGlobalInSmallSection(GO, TM, getKindForGlobal(GO, TM));
60 }
61
62 // Return true if this global address should be placed into small data/bss
63 // section.
isGlobalInSmallSection(const GlobalObject * GO,const TargetMachine & TM,SectionKind Kind) const64 bool LanaiTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
65 const TargetMachine &TM,
66 SectionKind Kind) const {
67 return isGlobalInSmallSectionImpl(GO, TM);
68 }
69
70 // Return true if this global address should be placed into small data/bss
71 // section. This method does all the work, except for checking the section
72 // kind.
isGlobalInSmallSectionImpl(const GlobalObject * GO,const TargetMachine & TM) const73 bool LanaiTargetObjectFile::isGlobalInSmallSectionImpl(
74 const GlobalObject *GO, const TargetMachine &TM) const {
75 const auto *GVA = dyn_cast<GlobalVariable>(GO);
76
77 // If not a GlobalVariable, only consider the code model.
78 if (!GVA) return TM.getCodeModel() == CodeModel::Small;
79
80 // Global values placed in sections starting with .ldata do not fit in
81 // 21-bits, so always use large memory access for them. FIXME: This is a
82 // workaround for a tool limitation.
83 if (GVA->getSection().starts_with(".ldata"))
84 return false;
85
86 if (TM.getCodeModel() == CodeModel::Small)
87 return true;
88
89 if (GVA->hasLocalLinkage())
90 return false;
91
92 if (((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||
93 GVA->hasCommonLinkage()))
94 return false;
95
96 Type *Ty = GVA->getValueType();
97 return isInSmallSection(
98 GVA->getDataLayout().getTypeAllocSize(Ty));
99 }
100
SelectSectionForGlobal(const GlobalObject * GO,SectionKind Kind,const TargetMachine & TM) const101 MCSection *LanaiTargetObjectFile::SelectSectionForGlobal(
102 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
103 // Handle Small Section classification here.
104 if (Kind.isBSS() && isGlobalInSmallSection(GO, TM, Kind))
105 return SmallBSSSection;
106 if (Kind.isData() && isGlobalInSmallSection(GO, TM, Kind))
107 return SmallDataSection;
108
109 // Otherwise, we work the same as ELF.
110 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
111 }
112
113 /// Return true if this constant should be placed into small data section.
isConstantInSmallSection(const DataLayout & DL,const Constant * CN) const114 bool LanaiTargetObjectFile::isConstantInSmallSection(const DataLayout &DL,
115 const Constant *CN) const {
116 return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
117 }
118
getSectionForConstant(const DataLayout & DL,SectionKind Kind,const Constant * C,Align & Alignment) const119 MCSection *LanaiTargetObjectFile::getSectionForConstant(
120 const DataLayout &DL, SectionKind Kind, const Constant *C,
121 Align &Alignment) const {
122 if (isConstantInSmallSection(DL, C))
123 return SmallDataSection;
124
125 // Otherwise, we work the same as ELF.
126 return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C,
127 Alignment);
128 }
129