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 
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.
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.
49 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.
64 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.
73 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().startswith(".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->getParent()->getDataLayout().getTypeAllocSize(Ty));
99 }
100 
101 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.
114 bool LanaiTargetObjectFile::isConstantInSmallSection(const DataLayout &DL,
115                                                      const Constant *CN) const {
116   return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
117 }
118 
119 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