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  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.
42static 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.
50bool 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.
65bool 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.
74bool 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
102MCSection *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.
115bool LanaiTargetObjectFile::isConstantInSmallSection(const DataLayout &DL,
116                                                     const Constant *CN) const {
117  return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
118}
119
120MCSection *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