1 //
2 //                     The LLVM Compiler Infrastructure
3 //
4 // This file is distributed under the University of Illinois Open Source
5 // License. See LICENSE.TXT for details.
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "LanaiTargetObjectFile.h"
10 
11 #include "LanaiSubtarget.h"
12 #include "LanaiTargetMachine.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/Support/ELF.h"
20 #include "llvm/Target/TargetMachine.h"
21 
22 using namespace llvm;
23 
24 static cl::opt<unsigned> SSThreshold(
25     "lanai-ssection-threshold", cl::Hidden,
26     cl::desc("Small data and bss section threshold size (default=0)"),
27     cl::init(0));
28 
29 void LanaiTargetObjectFile::Initialize(MCContext &Ctx,
30                                        const TargetMachine &TM) {
31   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
32   InitializeELF(TM.Options.UseInitArray);
33 
34   SmallDataSection = getContext().getELFSection(
35       ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
36   SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
37                                                ELF::SHF_WRITE | ELF::SHF_ALLOC);
38 }
39 
40 // A address must be loaded from a small section if its size is less than the
41 // small section size threshold. Data in this section must be addressed using
42 // gp_rel operator.
43 static bool isInSmallSection(uint64_t Size) {
44   // gcc has traditionally not treated zero-sized objects as small data, so this
45   // is effectively part of the ABI.
46   return Size > 0 && Size <= SSThreshold;
47 }
48 
49 // Return true if this global address should be placed into small data/bss
50 // section.
51 bool LanaiTargetObjectFile::isGlobalInSmallSection(
52     const GlobalValue *GV, const TargetMachine &TM) const {
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 (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
57     return isGlobalInSmallSectionImpl(GV, TM);
58 
59   return isGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
60 }
61 
62 // Return true if this global address should be placed into small data/bss
63 // section.
64 bool LanaiTargetObjectFile::isGlobalInSmallSection(const GlobalValue *GV,
65                                                    const TargetMachine &TM,
66                                                    SectionKind Kind) const {
67   return (isGlobalInSmallSectionImpl(GV, TM) &&
68           (Kind.isData() || Kind.isBSS() || Kind.isCommon()));
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 GlobalValue *GV, const TargetMachine & /*TM*/) const {
76   // Only global variables, not functions.
77   const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
78   if (!GVA)
79     return false;
80 
81   if (GV->hasLocalLinkage())
82     return false;
83 
84   if (((GV->hasExternalLinkage() && GV->isDeclaration()) ||
85        GV->hasCommonLinkage()))
86     return false;
87 
88   Type *Ty = GV->getType()->getElementType();
89   return isInSmallSection(
90       GV->getParent()->getDataLayout().getTypeAllocSize(Ty));
91 }
92 
93 MCSection *LanaiTargetObjectFile::SelectSectionForGlobal(
94     const GlobalValue *GV, SectionKind Kind, const TargetMachine &TM) const {
95   // Handle Small Section classification here.
96   if (Kind.isBSS() && isGlobalInSmallSection(GV, TM, Kind))
97     return SmallBSSSection;
98   if (Kind.isData() && isGlobalInSmallSection(GV, TM, Kind))
99     return SmallDataSection;
100 
101   // Otherwise, we work the same as ELF.
102   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, TM);
103 }
104 
105 /// Return true if this constant should be placed into small data section.
106 bool LanaiTargetObjectFile::isConstantInSmallSection(const DataLayout &DL,
107                                                      const Constant *CN) const {
108   return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
109 }
110 
111 MCSection *LanaiTargetObjectFile::getSectionForConstant(const DataLayout &DL,
112                                                         SectionKind Kind,
113                                                         const Constant *C,
114                                                         unsigned &Align) const {
115   if (isConstantInSmallSection(DL, C))
116     return SmallDataSection;
117 
118   // Otherwise, we work the same as ELF.
119   return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align);
120 }
121