llvm/lib/Target/RISCV/RISCVTargetObjectFile.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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "RISCVTargetObjectFile.h"
  10 #include "MCTargetDesc/RISCVMCObjectFileInfo.h"
  11 #include "RISCVTargetMachine.h"
  12 #include "llvm/BinaryFormat/ELF.h"
  13 #include "llvm/MC/MCContext.h"
  14 #include "llvm/MC/MCSectionELF.h"
  15
  16 using namespace llvm;
  17
  18 unsigned RISCVELFTargetObjectFile::getTextSectionAlignment() const {
  19   return RISCVMCObjectFileInfo::getTextSectionAlignment(
  20       *getContext().getSubtargetInfo());
  21 }
  22
  23 void RISCVELFTargetObjectFile::Initialize(MCContext &Ctx,
  24                                           const TargetMachine &TM) {
  25   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
  26
  27   PLTRelativeVariantKind = MCSymbolRefExpr::VK_PLT;
  28
  29   SmallDataSection = getContext().getELFSection(
  30       ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
  31   SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
  32                                                ELF::SHF_WRITE | ELF::SHF_ALLOC);
  33 }
  34
  35 // A address must be loaded from a small section if its size is less than the
  36 // small section size threshold. Data in this section could be addressed by
  37 // using gp_rel operator.
  38 bool RISCVELFTargetObjectFile::isInSmallSection(uint64_t Size) const {
  39   // gcc has traditionally not treated zero-sized objects as small data, so this
  40   // is effectively part of the ABI.
  41   return Size > 0 && Size <= SSThreshold;
  42 }
  43
  44 // Return true if this global address should be placed into small data/bss
  45 // section.
  46 bool RISCVELFTargetObjectFile::isGlobalInSmallSection(
  47     const GlobalObject *GO, const TargetMachine &TM) const {
  48   // Only global variables, not functions.
  49   const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GO);
  50   if (!GVA)
  51     return false;
  52
  53   // If the variable has an explicit section, it is placed in that section.
  54   if (GVA->hasSection()) {
  55     StringRef Section = GVA->getSection();
  56
  57     // Explicitly placing any variable in the small data section overrides
  58     // the global -G value.
  59     if (Section == ".sdata" || Section == ".sbss")
  60       return true;
  61
  62     // Otherwise reject putting the variable to small section if it has an
  63     // explicit section name.
  64     return false;
  65   }
  66
  67   if (((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||
  68        GVA->hasCommonLinkage()))
  69     return false;
  70
  71   Type *Ty = GVA->getValueType();
  72   // It is possible that the type of the global is unsized, i.e. a declaration
  73   // of a extern struct. In this case don't presume it is in the small data
  74   // section. This happens e.g. when building the FreeBSD kernel.
  75   if (!Ty->isSized())
  76     return false;
  77
  78   return isInSmallSection(
  79       GVA->getParent()->getDataLayout().getTypeAllocSize(Ty));
  80 }
  81
  82 MCSection *RISCVELFTargetObjectFile::SelectSectionForGlobal(
  83     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
  84   // Handle Small Section classification here.
  85   if (Kind.isBSS() && isGlobalInSmallSection(GO, TM))
  86     return SmallBSSSection;
  87   if (Kind.isData() && isGlobalInSmallSection(GO, TM))
  88     return SmallDataSection;
  89
  90   // Otherwise, we work the same as ELF.
  91   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
  92 }
  93
  94 void RISCVELFTargetObjectFile::getModuleMetadata(Module &M) {
  95   TargetLoweringObjectFileELF::getModuleMetadata(M);
  96   SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags;
  97   M.getModuleFlagsMetadata(ModuleFlags);
  98
  99   for (const auto &MFE : ModuleFlags) {
 100     StringRef Key = MFE.Key->getString();
 101     if (Key == "SmallDataLimit") {
 102       SSThreshold = mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue();
 103       break;
 104     }
 105   }
 106 }
 107
 108 /// Return true if this constant should be placed into small data section.
 109 bool RISCVELFTargetObjectFile::isConstantInSmallSection(
 110     const DataLayout &DL, const Constant *CN) const {
 111   return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
 112 }
 113
 114 MCSection *RISCVELFTargetObjectFile::getSectionForConstant(
 115     const DataLayout &DL, SectionKind Kind, const Constant *C,
 116     Align &Alignment) const {
 117   if (isConstantInSmallSection(DL, C))
 118     return SmallDataSection;
 119
 120   // Otherwise, we work the same as ELF.
 121   return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C,
 122                                                             Alignment);
 123 }