MipsTargetObjectFile.cpp revision c85dca66e68c9fa6ffa8471c64113b12d8d94fb1 
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#include "llvm/Support/ELF.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
30  SmallDataSection =
31    getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
32                               MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
33                               SectionKind::getDataRel());
34
35  SmallBSSSection =
36    getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
37                               MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
38                               SectionKind::getBSS());
39
40}
41
42// A address must be loaded from a small section if its size is less than the
43// small section size threshold. Data in this section must be addressed using
44// gp_rel operator.
45static bool IsInSmallSection(uint64_t Size) {
46  return Size > 0 && Size <= SSThreshold;
47}
48
49bool MipsTargetObjectFile::IsGlobalInSmallSection(const GlobalValue *GV,
50                                                const TargetMachine &TM) const {
51  if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
52    return false;
53
54  return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
55}
56
57/// IsGlobalInSmallSection - Return true if this global address should be
58/// placed into small data/bss section.
59bool MipsTargetObjectFile::
60IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
61                       SectionKind Kind) const {
62
63  // Only use small section for non linux targets.
64  const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
65  if (Subtarget.isLinux())
66    return false;
67
68  // Only global variables, not functions.
69  const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
70  if (!GVA)
71    return false;
72
73  // We can only do this for datarel or BSS objects for now.
74  if (!Kind.isBSS() && !Kind.isDataRel())
75    return false;
76
77  // If this is a internal constant string, there is a special
78  // section for it, but not in small data/bss.
79  if (Kind.isMergeable1ByteCString())
80    return false;
81
82  const Type *Ty = GV->getType()->getElementType();
83  return IsInSmallSection(TM.getTargetData()->getTypeAllocSize(Ty));
84}
85
86
87
88const MCSection *MipsTargetObjectFile::
89SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
90                       Mangler *Mang, const TargetMachine &TM) const {
91  // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
92  // sections?
93
94  // Handle Small Section classification here.
95  if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
96    return SmallBSSSection;
97  if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
98    return SmallDataSection;
99
100  // Otherwise, we work the same as ELF.
101  return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
102}
103