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 
28 void LanaiTargetObjectFile::Initialize(MCContext &Ctx,
29                                        const TargetMachine &TM) {
30   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
31   InitializeELF(TM.Options.UseInitArray);
32 
33   SmallDataSection = getContext().getELFSection(
34       ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
35   SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
36                                                ELF::SHF_WRITE | ELF::SHF_ALLOC);
37 }
38 
39 // A address must be loaded from a small section if its size is less than the
40 // small section size threshold. Data in this section must be addressed using
41 // gp_rel operator.
42 static bool isInSmallSection(uint64_t Size) {
43   // gcc has traditionally not treated zero-sized objects as small data, so this
44   // is effectively part of the ABI.
45   return Size > 0 && Size <= SSThreshold;
46 }
47 
48 // Return true if this global address should be placed into small data/bss
49 // section.
50 bool LanaiTargetObjectFile::isGlobalInSmallSection(
51     const GlobalObject *GO, const TargetMachine &TM) const {
52   if (GO == nullptr) return TM.getCodeModel() == CodeModel::Small;
53 
54   // We first check the case where global is a declaration, because finding
55   // section kind using getKindForGlobal() is only allowed for global
56   // definitions.
57   if (GO->isDeclaration() || GO->hasAvailableExternallyLinkage())
58     return isGlobalInSmallSectionImpl(GO, TM);
59 
60   return isGlobalInSmallSection(GO, TM, getKindForGlobal(GO, TM));
61 }
62 
63 // Return true if this global address should be placed into small data/bss
64 // section.
65 bool LanaiTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
66                                                    const TargetMachine &TM,
67                                                    SectionKind Kind) const {
68   return isGlobalInSmallSectionImpl(GO, TM);
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.
74 bool LanaiTargetObjectFile::isGlobalInSmallSectionImpl(
75     const GlobalObject *GO, const TargetMachine &TM) const {
76   const auto *GVA = dyn_cast<GlobalVariable>(GO);
77 
78   // If not a GlobalVariable, only consider the code model.
79   if (!GVA) return TM.getCodeModel() == CodeModel::Small;
80 
81   // Global values placed in sections starting with .ldata do not fit in
82   // 21-bits, so always use large memory access for them. FIXME: This is a
83   // workaround for a tool limitation.
84   if (GVA->getSection().startswith(".ldata"))
85     return false;
86 
87   if (TM.getCodeModel() == CodeModel::Small)
88     return true;
89 
90   if (GVA->hasLocalLinkage())
91     return false;
92 
93   if (((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||
94        GVA->hasCommonLinkage()))
95     return false;
96 
97   Type *Ty = GVA->getValueType();
98   return isInSmallSection(
99       GVA->getParent()->getDataLayout().getTypeAllocSize(Ty));
100 }
101 
102 MCSection *LanaiTargetObjectFile::SelectSectionForGlobal(
103     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
104   // Handle Small Section classification here.
105   if (Kind.isBSS() && isGlobalInSmallSection(GO, TM, Kind))
106     return SmallBSSSection;
107   if (Kind.isData() && isGlobalInSmallSection(GO, TM, Kind))
108     return SmallDataSection;
109 
110   // Otherwise, we work the same as ELF.
111   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
112 }
113 
114 /// Return true if this constant should be placed into small data section.
115 bool LanaiTargetObjectFile::isConstantInSmallSection(const DataLayout &DL,
116                                                      const Constant *CN) const {
117   return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
118 }
119 
120 MCSection *LanaiTargetObjectFile::getSectionForConstant(const DataLayout &DL,
121                                                         SectionKind Kind,
122                                                         const Constant *C,
123                                                         unsigned &Align) const {
124   if (isConstantInSmallSection(DL, C))
125     return SmallDataSection;
126 
127   // Otherwise, we work the same as ELF.
128   return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align);
129 }
130