1 //===-- MipsTargetObjectFile.cpp - Mips object files ----------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "MipsTargetObjectFile.h"
11 #include "llvm/DerivedTypes.h"
12 #include "llvm/GlobalVariable.h"
13 #include "llvm/MC/MCSectionELF.h"
14 #include "llvm/Target/TargetData.h"
15 #include "llvm/Target/TargetMachine.h"
16 #include "llvm/Support/CommandLine.h"
17 using namespace llvm;
18 
19 static cl::opt<unsigned>
20 SSThreshold("mips-ssection-threshold", cl::Hidden,
21             cl::desc("Small data and bss section threshold size (default=8)"),
22             cl::init(8));
23 
24 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
25   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
26 
27   SmallDataSection =
28     getELFSection(".sdata", MCSectionELF::SHT_PROGBITS,
29                   MCSectionELF::SHF_WRITE | MCSectionELF::SHF_ALLOC,
30                   SectionKind::getDataRel());
31 
32   SmallBSSSection =
33     getELFSection(".sbss", MCSectionELF::SHT_NOBITS,
34                   MCSectionELF::SHF_WRITE | MCSectionELF::SHF_ALLOC,
35                   SectionKind::getBSS());
36 
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.
42 static bool IsInSmallSection(uint64_t Size) {
43   return Size > 0 && Size <= SSThreshold;
44 }
45 
46 bool MipsTargetObjectFile::IsGlobalInSmallSection(const GlobalValue *GV,
47                                                 const TargetMachine &TM) const {
48   if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
49     return false;
50 
51   return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
52 }
53 
54 /// IsGlobalInSmallSection - Return true if this global address should be
55 /// placed into small data/bss section.
56 bool MipsTargetObjectFile::
57 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
58                        SectionKind Kind) const {
59   // Only global variables, not functions.
60   const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
61   if (!GVA)
62     return false;
63 
64   // We can only do this for datarel or BSS objects for now.
65   if (!Kind.isBSS() && !Kind.isDataRel())
66     return false;
67 
68   // If this is a internal constant string, there is a special
69   // section for it, but not in small data/bss.
70   if (Kind.isMergeable1ByteCString())
71     return false;
72 
73   const Type *Ty = GV->getType()->getElementType();
74   return IsInSmallSection(TM.getTargetData()->getTypeAllocSize(Ty));
75 }
76 
77 
78 
79 const MCSection *MipsTargetObjectFile::
80 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
81                        Mangler *Mang, const TargetMachine &TM) const {
82   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
83   // sections?
84 
85   // Handle Small Section classification here.
86   if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
87     return SmallBSSSection;
88   if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
89     return SmallDataSection;
90 
91   // Otherwise, we work the same as ELF.
92   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
93 }
94