MipsTargetObjectFile.cpp revision d04a8d4b33ff316ca4cf961e06c9e312eff8e64f 
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/DataLayout.h"
13#include "llvm/DerivedTypes.h"
14#include "llvm/GlobalVariable.h"
15#include "llvm/MC/MCContext.h"
16#include "llvm/MC/MCSectionELF.h"
17#include "llvm/Support/CommandLine.h"
18#include "llvm/Support/ELF.h"
19#include "llvm/Target/TargetMachine.h"
20using namespace llvm;
21
22static cl::opt<unsigned>
23SSThreshold("mips-ssection-threshold", cl::Hidden,
24            cl::desc("Small data and bss section threshold size (default=8)"),
25            cl::init(8));
26
27void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
28  TargetLoweringObjectFileELF::Initialize(Ctx, TM);
29  InitializeELF(TM.Options.UseInitArray);
30
31  SmallDataSection =
32    getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
33                               ELF::SHF_WRITE |ELF::SHF_ALLOC,
34                               SectionKind::getDataRel());
35
36  SmallBSSSection =
37    getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
38                               ELF::SHF_WRITE |ELF::SHF_ALLOC,
39                               SectionKind::getBSS());
40
41}
42
43// A address must be loaded from a small section if its size is less than the
44// small section size threshold. Data in this section must be addressed using
45// gp_rel operator.
46static bool IsInSmallSection(uint64_t Size) {
47  return Size > 0 && Size <= SSThreshold;
48}
49
50bool MipsTargetObjectFile::IsGlobalInSmallSection(const GlobalValue *GV,
51                                                const TargetMachine &TM) const {
52  if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
53    return false;
54
55  return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
56}
57
58/// IsGlobalInSmallSection - Return true if this global address should be
59/// placed into small data/bss section.
60bool MipsTargetObjectFile::
61IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
62                       SectionKind Kind) const {
63
64  const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
65
66  // Return if small section is not available.
67  if (!Subtarget.useSmallSection())
68    return false;
69
70  // Only global variables, not functions.
71  const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
72  if (!GVA)
73    return false;
74
75  // We can only do this for datarel or BSS objects for now.
76  if (!Kind.isBSS() && !Kind.isDataRel())
77    return false;
78
79  // If this is a internal constant string, there is a special
80  // section for it, but not in small data/bss.
81  if (Kind.isMergeable1ByteCString())
82    return false;
83
84  Type *Ty = GV->getType()->getElementType();
85  return IsInSmallSection(TM.getDataLayout()->getTypeAllocSize(Ty));
86}
87
88
89
90const MCSection *MipsTargetObjectFile::
91SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
92                       Mangler *Mang, const TargetMachine &TM) const {
93  // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
94  // sections?
95
96  // Handle Small Section classification here.
97  if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
98    return SmallBSSSection;
99  if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
100    return SmallDataSection;
101
102  // Otherwise, we work the same as ELF.
103  return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
104}
105