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 "llvm/BinaryFormat/ELF.h"
11#include "llvm/IR/DataLayout.h"
12#include "llvm/IR/GlobalVariable.h"
13#include "llvm/MC/MCContext.h"
14#include "llvm/MC/MCSectionELF.h"
15#include "llvm/Support/CommandLine.h"
16#include "llvm/Target/TargetMachine.h"
17
18using namespace llvm;
19
20static cl::opt<unsigned> SSThreshold(
21 "lanai-ssection-threshold", cl::Hidden,
22 cl::desc("Small data and bss section threshold size (default=0)"),
23 cl::init(Val: 0));
24
25void LanaiTargetObjectFile::Initialize(MCContext &Ctx,
26 const TargetMachine &TM) {
27 TargetLoweringObjectFileELF::Initialize(Ctx, TM);
28
29 SmallDataSection = getContext().getELFSection(
30 Section: ".sdata", Type: ELF::SHT_PROGBITS, Flags: ELF::SHF_WRITE | ELF::SHF_ALLOC);
31 SmallBSSSection = getContext().getELFSection(Section: ".sbss", Type: ELF::SHT_NOBITS,
32 Flags: ELF::SHF_WRITE | ELF::SHF_ALLOC);
33}
34
35// A address must be loaded from a small section if its size is less than the
36// small section size threshold. Data in this section must be addressed using
37// gp_rel operator.
38static bool isInSmallSection(uint64_t Size) {
39 // gcc has traditionally not treated zero-sized objects as small data, so this
40 // is effectively part of the ABI.
41 return Size > 0 && Size <= SSThreshold;
42}
43
44// Return true if this global address should be placed into small data/bss
45// section.
46bool LanaiTargetObjectFile::isGlobalInSmallSection(
47 const GlobalObject *GO, const TargetMachine &TM) const {
48 if (GO == nullptr) return TM.getCodeModel() == CodeModel::Small;
49
50 // We first check the case where global is a declaration, because finding
51 // section kind using getKindForGlobal() is only allowed for global
52 // definitions.
53 if (GO->isDeclaration() || GO->hasAvailableExternallyLinkage())
54 return isGlobalInSmallSectionImpl(GO, TM);
55
56 return isGlobalInSmallSection(GO, TM, Kind: getKindForGlobal(GO, TM));
57}
58
59// Return true if this global address should be placed into small data/bss
60// section.
61bool LanaiTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
62 const TargetMachine &TM,
63 SectionKind Kind) const {
64 return isGlobalInSmallSectionImpl(GO, TM);
65}
66
67// Return true if this global address should be placed into small data/bss
68// section. This method does all the work, except for checking the section
69// kind.
70bool LanaiTargetObjectFile::isGlobalInSmallSectionImpl(
71 const GlobalObject *GO, const TargetMachine &TM) const {
72 const auto *GVA = dyn_cast<GlobalVariable>(Val: GO);
73
74 // If not a GlobalVariable, only consider the code model.
75 if (!GVA) return TM.getCodeModel() == CodeModel::Small;
76
77 // Global values placed in sections starting with .ldata do not fit in
78 // 21-bits, so always use large memory access for them. FIXME: This is a
79 // workaround for a tool limitation.
80 if (GVA->getSection().starts_with(Prefix: ".ldata"))
81 return false;
82
83 if (TM.getCodeModel() == CodeModel::Small)
84 return true;
85
86 if (GVA->hasLocalLinkage())
87 return false;
88
89 if (((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||
90 GVA->hasCommonLinkage()))
91 return false;
92
93 Type *Ty = GVA->getValueType();
94 return isInSmallSection(
95 Size: GVA->getDataLayout().getTypeAllocSize(Ty));
96}
97
98MCSection *LanaiTargetObjectFile::SelectSectionForGlobal(
99 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
100 // Handle Small Section classification here.
101 if (Kind.isBSS() && isGlobalInSmallSection(GO, TM, Kind))
102 return SmallBSSSection;
103 if (Kind.isData() && isGlobalInSmallSection(GO, TM, Kind))
104 return SmallDataSection;
105
106 // Otherwise, we work the same as ELF.
107 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
108}
109
110/// Return true if this constant should be placed into small data section.
111bool LanaiTargetObjectFile::isConstantInSmallSection(const DataLayout &DL,
112 const Constant *CN) const {
113 return isInSmallSection(Size: DL.getTypeAllocSize(Ty: CN->getType()));
114}
115
116MCSection *LanaiTargetObjectFile::getSectionForConstant(
117 const DataLayout &DL, SectionKind Kind, const Constant *C,
118 Align &Alignment) const {
119 if (isConstantInSmallSection(DL, CN: C))
120 return SmallDataSection;
121
122 // Otherwise, we work the same as ELF.
123 return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C,
124 Alignment);
125}
126