1 //===-- RISCVTargetObjectFile.cpp - RISCV Object Info -----------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "RISCVTargetObjectFile.h"
10 #include "RISCVTargetMachine.h"
11 #include "llvm/BinaryFormat/ELF.h"
12 #include "llvm/MC/MCContext.h"
13 #include "llvm/MC/MCSectionELF.h"
14
15 using namespace llvm;
16
Initialize(MCContext & Ctx,const TargetMachine & TM)17 void RISCVELFTargetObjectFile::Initialize(MCContext &Ctx,
18 const TargetMachine &TM) {
19 TargetLoweringObjectFileELF::Initialize(Ctx, TM);
20
21 SmallDataSection = getContext().getELFSection(
22 ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
23 SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
24 ELF::SHF_WRITE | ELF::SHF_ALLOC);
25 }
26
27 // A address must be loaded from a small section if its size is less than the
28 // small section size threshold. Data in this section could be addressed by
29 // using gp_rel operator.
isInSmallSection(uint64_t Size) const30 bool RISCVELFTargetObjectFile::isInSmallSection(uint64_t Size) const {
31 // gcc has traditionally not treated zero-sized objects as small data, so this
32 // is effectively part of the ABI.
33 return Size > 0 && Size <= SSThreshold;
34 }
35
36 // Return true if this global address should be placed into small data/bss
37 // section.
isGlobalInSmallSection(const GlobalObject * GO,const TargetMachine & TM) const38 bool RISCVELFTargetObjectFile::isGlobalInSmallSection(
39 const GlobalObject *GO, const TargetMachine &TM) const {
40 // Only global variables, not functions.
41 const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GO);
42 if (!GVA)
43 return false;
44
45 // If the variable has an explicit section, it is placed in that section.
46 if (GVA->hasSection()) {
47 StringRef Section = GVA->getSection();
48
49 // Explicitly placing any variable in the small data section overrides
50 // the global -G value.
51 if (Section == ".sdata" || Section == ".sbss")
52 return true;
53
54 // Otherwise reject putting the variable to small section if it has an
55 // explicit section name.
56 return false;
57 }
58
59 if (((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||
60 GVA->hasCommonLinkage()))
61 return false;
62
63 Type *Ty = GVA->getValueType();
64 // It is possible that the type of the global is unsized, i.e. a declaration
65 // of a extern struct. In this case don't presume it is in the small data
66 // section. This happens e.g. when building the FreeBSD kernel.
67 if (!Ty->isSized())
68 return false;
69
70 return isInSmallSection(
71 GVA->getParent()->getDataLayout().getTypeAllocSize(Ty));
72 }
73
SelectSectionForGlobal(const GlobalObject * GO,SectionKind Kind,const TargetMachine & TM) const74 MCSection *RISCVELFTargetObjectFile::SelectSectionForGlobal(
75 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
76 // Handle Small Section classification here.
77 if (Kind.isBSS() && isGlobalInSmallSection(GO, TM))
78 return SmallBSSSection;
79 if (Kind.isData() && isGlobalInSmallSection(GO, TM))
80 return SmallDataSection;
81
82 // Otherwise, we work the same as ELF.
83 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
84 }
85
getModuleMetadata(Module & M)86 void RISCVELFTargetObjectFile::getModuleMetadata(Module &M) {
87 TargetLoweringObjectFileELF::getModuleMetadata(M);
88 SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags;
89 M.getModuleFlagsMetadata(ModuleFlags);
90
91 for (const auto &MFE : ModuleFlags) {
92 StringRef Key = MFE.Key->getString();
93 if (Key == "SmallDataLimit") {
94 SSThreshold = mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue();
95 break;
96 }
97 }
98 }
99
100 /// Return true if this constant should be placed into small data section.
isConstantInSmallSection(const DataLayout & DL,const Constant * CN) const101 bool RISCVELFTargetObjectFile::isConstantInSmallSection(
102 const DataLayout &DL, const Constant *CN) const {
103 return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
104 }
105
getSectionForConstant(const DataLayout & DL,SectionKind Kind,const Constant * C,Align & Alignment) const106 MCSection *RISCVELFTargetObjectFile::getSectionForConstant(
107 const DataLayout &DL, SectionKind Kind, const Constant *C,
108 Align &Alignment) const {
109 if (isConstantInSmallSection(DL, C))
110 return SmallDataSection;
111
112 // Otherwise, we work the same as ELF.
113 return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C,
114 Alignment);
115 }
116