182 lines · cpp
1//===-- RISCVTargetObjectFile.cpp - RISC-V 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-exception6//7//===----------------------------------------------------------------------===//8 9#include "RISCVTargetObjectFile.h"10#include "MCTargetDesc/RISCVMCObjectFileInfo.h"11#include "RISCVTargetMachine.h"12#include "llvm/BinaryFormat/ELF.h"13#include "llvm/IR/Module.h"14#include "llvm/MC/MCContext.h"15#include "llvm/MC/MCSectionELF.h"16#include "llvm/MC/MCValue.h"17 18using namespace llvm;19 20unsigned RISCVELFTargetObjectFile::getTextSectionAlignment() const {21 return RISCVMCObjectFileInfo::getTextSectionAlignment(22 *getContext().getSubtargetInfo());23}24 25void RISCVELFTargetObjectFile::Initialize(MCContext &Ctx,26 const TargetMachine &TM) {27 TargetLoweringObjectFileELF::Initialize(Ctx, TM);28 29 PLTPCRelativeSpecifier = ELF::R_RISCV_PLT32;30 SupportIndirectSymViaGOTPCRel = true;31 32 SmallDataSection = getContext().getELFSection(33 ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);34 SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,35 ELF::SHF_WRITE | ELF::SHF_ALLOC);36 SmallRODataSection =37 getContext().getELFSection(".srodata", ELF::SHT_PROGBITS, ELF::SHF_ALLOC);38 SmallROData4Section = getContext().getELFSection(39 ".srodata.cst4", ELF::SHT_PROGBITS, ELF::SHF_ALLOC | ELF::SHF_MERGE, 4);40 SmallROData8Section = getContext().getELFSection(41 ".srodata.cst8", ELF::SHT_PROGBITS, ELF::SHF_ALLOC | ELF::SHF_MERGE, 8);42 SmallROData16Section = getContext().getELFSection(43 ".srodata.cst16", ELF::SHT_PROGBITS, ELF::SHF_ALLOC | ELF::SHF_MERGE, 16);44 SmallROData32Section = getContext().getELFSection(45 ".srodata.cst32", ELF::SHT_PROGBITS, ELF::SHF_ALLOC | ELF::SHF_MERGE, 32);46}47 48const MCExpr *RISCVELFTargetObjectFile::getIndirectSymViaGOTPCRel(49 const GlobalValue *GV, const MCSymbol *Sym, const MCValue &MV,50 int64_t Offset, MachineModuleInfo *MMI, MCStreamer &Streamer) const {51 auto &Ctx = getContext();52 const MCExpr *Res = MCSymbolRefExpr::create(Sym, Ctx);53 Res = MCBinaryExpr::createAdd(54 Res, MCConstantExpr::create(Offset + MV.getConstant(), Ctx), Ctx);55 return MCSpecifierExpr::create(Res, ELF::R_RISCV_GOT32_PCREL, Ctx);56}57 58// A address must be loaded from a small section if its size is less than the59// small section size threshold. Data in this section could be addressed by60// using gp_rel operator.61bool RISCVELFTargetObjectFile::isInSmallSection(uint64_t Size) const {62 // gcc has traditionally not treated zero-sized objects as small data, so this63 // is effectively part of the ABI.64 return Size > 0 && Size <= SSThreshold;65}66 67// Return true if this global address should be placed into small data/bss68// section.69bool RISCVELFTargetObjectFile::isGlobalInSmallSection(70 const GlobalObject *GO, const TargetMachine &TM) const {71 // Only global variables, not functions.72 const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GO);73 if (!GVA)74 return false;75 76 // If the variable has an explicit section, it is placed in that section.77 if (GVA->hasSection()) {78 StringRef Section = GVA->getSection();79 80 // Explicitly placing any variable in the small data section overrides81 // the global -G value.82 if (Section == ".sdata" || Section == ".sbss")83 return true;84 85 // Otherwise reject putting the variable to small section if it has an86 // explicit section name.87 return false;88 }89 90 if (((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||91 GVA->hasCommonLinkage()))92 return false;93 94 Type *Ty = GVA->getValueType();95 // It is possible that the type of the global is unsized, i.e. a declaration96 // of a extern struct. In this case don't presume it is in the small data97 // section. This happens e.g. when building the FreeBSD kernel.98 if (!Ty->isSized())99 return false;100 101 return isInSmallSection(102 GVA->getDataLayout().getTypeAllocSize(Ty));103}104 105MCSection *RISCVELFTargetObjectFile::SelectSectionForGlobal(106 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {107 // Handle Small Section classification here.108 if (isGlobalInSmallSection(GO, TM)) {109 // Emit to an unique sdata/sbss section when -fdata-section is set.110 // However, if a symbol has an explicit sdata/sbss section, place it in that111 // section.112 bool EmitUniquedSection = TM.getDataSections() && !GO->hasSection();113 114 if (Kind.isBSS()) {115 if (EmitUniquedSection) {116 SmallString<128> Name(".sbss.");117 Name.append(GO->getName());118 return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,119 ELF::SHF_WRITE | ELF::SHF_ALLOC);120 }121 122 return SmallBSSSection;123 }124 125 if (Kind.isData()) {126 if (EmitUniquedSection) {127 SmallString<128> Name(".sdata.");128 Name.append(GO->getName());129 return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,130 ELF::SHF_WRITE | ELF::SHF_ALLOC);131 }132 133 return SmallDataSection;134 }135 }136 137 // Otherwise, we work the same as ELF.138 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);139}140 141void RISCVELFTargetObjectFile::getModuleMetadata(Module &M) {142 TargetLoweringObjectFileELF::getModuleMetadata(M);143 SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags;144 M.getModuleFlagsMetadata(ModuleFlags);145 146 for (const auto &MFE : ModuleFlags) {147 StringRef Key = MFE.Key->getString();148 if (Key == "SmallDataLimit") {149 SSThreshold = mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue();150 break;151 }152 }153}154 155/// Return true if this constant should be placed into small data section.156bool RISCVELFTargetObjectFile::isConstantInSmallSection(157 const DataLayout &DL, const Constant *CN) const {158 return isInSmallSection(DL.getTypeAllocSize(CN->getType()));159}160 161MCSection *RISCVELFTargetObjectFile::getSectionForConstant(162 const DataLayout &DL, SectionKind Kind, const Constant *C,163 Align &Alignment) const {164 if (C && isConstantInSmallSection(DL, C)) {165 if (Kind.isMergeableConst4())166 return SmallROData4Section;167 if (Kind.isMergeableConst8())168 return SmallROData8Section;169 if (Kind.isMergeableConst16())170 return SmallROData16Section;171 if (Kind.isMergeableConst32())172 return SmallROData32Section;173 // LLVM only generate up to .rodata.cst32, and use .rodata section if more174 // than 32 bytes, so just use .srodata here.175 return SmallRODataSection;176 }177 178 // Otherwise, we work the same as ELF.179 return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C,180 Alignment);181}182