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 "MipsSubtarget.h"
12 #include "llvm/DerivedTypes.h"
13 #include "llvm/GlobalVariable.h"
14 #include "llvm/MC/MCContext.h"
15 #include "llvm/MC/MCSectionELF.h"
16 #include "llvm/Target/TargetData.h"
17 #include "llvm/Target/TargetMachine.h"
18 #include "llvm/Support/CommandLine.h"
19 using namespace llvm;
20 
21 static cl::opt<unsigned>
22 SSThreshold("mips-ssection-threshold", cl::Hidden,
23             cl::desc("Small data and bss section threshold size (default=8)"),
24             cl::init(8));
25 
26 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
27   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
28 
29   SmallDataSection =
30     getContext().getELFSection(".sdata", MCSectionELF::SHT_PROGBITS,
31                                MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
32                                SectionKind::getDataRel());
33 
34   SmallBSSSection =
35     getContext().getELFSection(".sbss", MCSectionELF::SHT_NOBITS,
36                                MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
37                                SectionKind::getBSS());
38 
39 }
40 
41 // A address must be loaded from a small section if its size is less than the
42 // small section size threshold. Data in this section must be addressed using
43 // gp_rel operator.
44 static bool IsInSmallSection(uint64_t Size) {
45   return Size > 0 && Size <= SSThreshold;
46 }
47 
48 bool MipsTargetObjectFile::IsGlobalInSmallSection(const GlobalValue *GV,
49                                                 const TargetMachine &TM) const {
50   if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
51     return false;
52 
53   return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
54 }
55 
56 /// IsGlobalInSmallSection - Return true if this global address should be
57 /// placed into small data/bss section.
58 bool MipsTargetObjectFile::
59 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
60                        SectionKind Kind) const {
61 
62   // Only use small section for non linux targets.
63   const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
64   if (Subtarget.isLinux())
65     return false;
66 
67   // Only global variables, not functions.
68   const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
69   if (!GVA)
70     return false;
71 
72   // We can only do this for datarel or BSS objects for now.
73   if (!Kind.isBSS() && !Kind.isDataRel())
74     return false;
75 
76   // If this is a internal constant string, there is a special
77   // section for it, but not in small data/bss.
78   if (Kind.isMergeable1ByteCString())
79     return false;
80 
81   const Type *Ty = GV->getType()->getElementType();
82   return IsInSmallSection(TM.getTargetData()->getTypeAllocSize(Ty));
83 }
84 
85 
86 
87 const MCSection *MipsTargetObjectFile::
88 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
89                        Mangler *Mang, const TargetMachine &TM) const {
90   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
91   // sections?
92 
93   // Handle Small Section classification here.
94   if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
95     return SmallBSSSection;
96   if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
97     return SmallDataSection;
98 
99   // Otherwise, we work the same as ELF.
100   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
101 }
102