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
21using namespace llvm;
22
23static 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
28void 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.
41static 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.
49bool 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.
64bool 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.
73bool 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
101MCSection *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.
114bool LanaiTargetObjectFile::isConstantInSmallSection(const DataLayout &DL,
115                                                     const Constant *CN) const {
116  return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
117}
118
119MCSection *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