forked from OSchip/llvm-project
196 lines
7.4 KiB
C++
196 lines
7.4 KiB
C++
//===-- MipsTargetObjectFile.cpp - Mips Object Files ----------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "MipsTargetObjectFile.h"
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#include "MipsSubtarget.h"
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#include "MipsTargetMachine.h"
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#include "MCTargetDesc/MipsMCExpr.h"
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#include "llvm/BinaryFormat/ELF.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCSectionELF.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Target/TargetMachine.h"
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using namespace llvm;
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static cl::opt<unsigned>
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SSThreshold("mips-ssection-threshold", cl::Hidden,
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cl::desc("Small data and bss section threshold size (default=8)"),
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cl::init(8));
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static cl::opt<bool>
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LocalSData("mlocal-sdata", cl::Hidden,
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cl::desc("MIPS: Use gp_rel for object-local data."),
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cl::init(true));
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static cl::opt<bool>
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ExternSData("mextern-sdata", cl::Hidden,
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cl::desc("MIPS: Use gp_rel for data that is not defined by the "
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"current object."),
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cl::init(true));
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static cl::opt<bool>
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EmbeddedData("membedded-data", cl::Hidden,
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cl::desc("MIPS: Try to allocate variables in the following"
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" sections if possible: .rodata, .sdata, .data ."),
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cl::init(false));
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void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
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TargetLoweringObjectFileELF::Initialize(Ctx, TM);
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InitializeELF(TM.Options.UseInitArray);
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SmallDataSection = getContext().getELFSection(
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".sdata", ELF::SHT_PROGBITS,
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ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_MIPS_GPREL);
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SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
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ELF::SHF_WRITE | ELF::SHF_ALLOC |
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ELF::SHF_MIPS_GPREL);
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this->TM = &static_cast<const MipsTargetMachine &>(TM);
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}
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// A address must be loaded from a small section if its size is less than the
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// small section size threshold. Data in this section must be addressed using
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// gp_rel operator.
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static bool IsInSmallSection(uint64_t Size) {
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// gcc has traditionally not treated zero-sized objects as small data, so this
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// is effectively part of the ABI.
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return Size > 0 && Size <= SSThreshold;
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}
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/// Return true if this global address should be placed into small data/bss
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/// section.
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bool MipsTargetObjectFile::IsGlobalInSmallSection(
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const GlobalObject *GO, const TargetMachine &TM) const {
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// We first check the case where global is a declaration, because finding
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// section kind using getKindForGlobal() is only allowed for global
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// definitions.
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if (GO->isDeclaration() || GO->hasAvailableExternallyLinkage())
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return IsGlobalInSmallSectionImpl(GO, TM);
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return IsGlobalInSmallSection(GO, TM, getKindForGlobal(GO, TM));
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}
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/// Return true if this global address should be placed into small data/bss
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/// section.
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bool MipsTargetObjectFile::
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IsGlobalInSmallSection(const GlobalObject *GO, const TargetMachine &TM,
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SectionKind Kind) const {
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return IsGlobalInSmallSectionImpl(GO, TM) &&
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(Kind.isData() || Kind.isBSS() || Kind.isCommon() ||
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Kind.isReadOnly());
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}
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/// Return true if this global address should be placed into small data/bss
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/// section. This method does all the work, except for checking the section
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/// kind.
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bool MipsTargetObjectFile::
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IsGlobalInSmallSectionImpl(const GlobalObject *GO,
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const TargetMachine &TM) const {
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const MipsSubtarget &Subtarget =
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*static_cast<const MipsTargetMachine &>(TM).getSubtargetImpl();
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// Return if small section is not available.
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if (!Subtarget.useSmallSection())
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return false;
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// Only global variables, not functions.
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const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GO);
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if (!GVA)
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return false;
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// If the variable has an explicit section, it is placed in that section but
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// it's addressing mode may change.
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if (GVA->hasSection()) {
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StringRef Section = GVA->getSection();
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// Explicitly placing any variable in the small data section overrides
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// the global -G value.
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if (Section == ".sdata" || Section == ".sbss")
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return true;
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// Otherwise reject accessing it through the gp pointer. There are some
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// historic cases which GCC doesn't appear to respect any more. These
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// are .lit4, .lit8 and .srdata. For the moment reject these as well.
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return false;
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}
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// Enforce -mlocal-sdata.
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if (!LocalSData && GVA->hasLocalLinkage())
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return false;
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// Enforce -mextern-sdata.
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if (!ExternSData && ((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||
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GVA->hasCommonLinkage()))
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return false;
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// Enforce -membedded-data.
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if (EmbeddedData && GVA->isConstant())
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return false;
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Type *Ty = GVA->getValueType();
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// It is possible that the type of the global is unsized, i.e. a declaration
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// of a extern struct. In this case don't presume it is in the small data
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// section. This happens e.g. when building the FreeBSD kernel.
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if (!Ty->isSized())
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return false;
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return IsInSmallSection(
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GVA->getParent()->getDataLayout().getTypeAllocSize(Ty));
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}
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MCSection *MipsTargetObjectFile::SelectSectionForGlobal(
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const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
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// TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
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// sections?
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// Handle Small Section classification here.
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if (Kind.isBSS() && IsGlobalInSmallSection(GO, TM, Kind))
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return SmallBSSSection;
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if (Kind.isData() && IsGlobalInSmallSection(GO, TM, Kind))
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return SmallDataSection;
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if (Kind.isReadOnly() && IsGlobalInSmallSection(GO, TM, Kind))
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return SmallDataSection;
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// Otherwise, we work the same as ELF.
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return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
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}
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/// Return true if this constant should be placed into small data section.
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bool MipsTargetObjectFile::IsConstantInSmallSection(
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const DataLayout &DL, const Constant *CN, const TargetMachine &TM) const {
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return (static_cast<const MipsTargetMachine &>(TM)
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.getSubtargetImpl()
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->useSmallSection() &&
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LocalSData && IsInSmallSection(DL.getTypeAllocSize(CN->getType())));
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}
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/// Return true if this constant should be placed into small data section.
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MCSection *MipsTargetObjectFile::getSectionForConstant(const DataLayout &DL,
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SectionKind Kind,
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const Constant *C,
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unsigned &Align) const {
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if (IsConstantInSmallSection(DL, C, *TM))
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return SmallDataSection;
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// Otherwise, we work the same as ELF.
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return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align);
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}
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const MCExpr *
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MipsTargetObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
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const MCExpr *Expr =
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MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_None, getContext());
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Expr = MCBinaryExpr::createAdd(
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Expr, MCConstantExpr::create(0x8000, getContext()), getContext());
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return MipsMCExpr::create(MipsMCExpr::MEK_DTPREL, Expr, getContext());
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}
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