lib/Target/ARM/ARMTargetObjectFile.cpp

   1 //===-- llvm/Target/ARMTargetObjectFile.cpp - ARM Object Info Impl --------===//
   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 "ARMTargetObjectFile.h"
  10 #include "ARMSubtarget.h"
  11 #include "ARMTargetMachine.h"
  12 #include "llvm/BinaryFormat/Dwarf.h"
  13 #include "llvm/BinaryFormat/ELF.h"
  14 #include "llvm/MC/MCAsmInfo.h"
  15 #include "llvm/MC/MCContext.h"
  16 #include "llvm/MC/MCExpr.h"
  17 #include "llvm/MC/MCSectionELF.h"
  18 #include "llvm/MC/MCTargetOptions.h"
  19 #include "llvm/MC/SectionKind.h"
  20 #include "llvm/Target/TargetMachine.h"
  21 #include <cassert>
  22
  23 using namespace llvm;
  24 using namespace dwarf;
  25
  26 //===----------------------------------------------------------------------===//
  27 //                               ELF Target
  28 //===----------------------------------------------------------------------===//
  29
  30 void ARMElfTargetObjectFile::Initialize(MCContext &Ctx,
  31                                         const TargetMachine &TM) {
  32   const ARMBaseTargetMachine &ARM_TM = static_cast<const ARMBaseTargetMachine &>(TM);
  33   bool isAAPCS_ABI = ARM_TM.TargetABI == ARMBaseTargetMachine::ARMABI::ARM_ABI_AAPCS;
  34   bool genExecuteOnly =
  35       ARM_TM.getMCSubtargetInfo()->hasFeature(ARM::FeatureExecuteOnly);
  36
  37   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
  38   InitializeELF(isAAPCS_ABI);
  39
  40   if (isAAPCS_ABI) {
  41     LSDASection = nullptr;
  42   }
  43
  44   // Make code section unreadable when in execute-only mode
  45   if (genExecuteOnly) {
  46     unsigned Type = ELF::SHT_PROGBITS;
  47     unsigned Flags =
  48         ELF::SHF_EXECINSTR | ELF::SHF_ALLOC | ELF::SHF_ARM_PURECODE;
  49     // Since we cannot modify flags for an existing section, we create a new
  50     // section with the right flags, and use 0 as the unique ID for
  51     // execute-only text
  52     TextSection = Ctx.getELFSection(".text", Type, Flags, 0, "", 0U);
  53   }
  54 }
  55
  56 const MCExpr *ARMElfTargetObjectFile::getTTypeGlobalReference(
  57     const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
  58     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
  59   if (TM.getMCAsmInfo()->getExceptionHandlingType() != ExceptionHandling::ARM)
  60     return TargetLoweringObjectFileELF::getTTypeGlobalReference(
  61         GV, Encoding, TM, MMI, Streamer);
  62
  63   assert(Encoding == DW_EH_PE_absptr && "Can handle absptr encoding only");
  64
  65   return MCSymbolRefExpr::create(TM.getSymbol(GV),
  66                                  MCSymbolRefExpr::VK_ARM_TARGET2, getContext());
  67 }
  68
  69 const MCExpr *ARMElfTargetObjectFile::
  70 getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
  71   return MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_ARM_TLSLDO,
  72                                  getContext());
  73 }
  74
  75 static bool isExecuteOnlyFunction(const GlobalObject *GO, SectionKind SK,
  76                                   const TargetMachine &TM) {
  77   if (const Function *F = dyn_cast<Function>(GO))
  78     if (TM.getSubtarget<ARMSubtarget>(*F).genExecuteOnly() && SK.isText())
  79       return true;
  80   return false;
  81 }
  82
  83 MCSection *ARMElfTargetObjectFile::getExplicitSectionGlobal(
  84     const GlobalObject *GO, SectionKind SK, const TargetMachine &TM) const {
  85   // Set execute-only access for the explicit section
  86   if (isExecuteOnlyFunction(GO, SK, TM))
  87     SK = SectionKind::getExecuteOnly();
  88
  89   return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, SK, TM);
  90 }
  91
  92 MCSection *ARMElfTargetObjectFile::SelectSectionForGlobal(
  93     const GlobalObject *GO, SectionKind SK, const TargetMachine &TM) const {
  94   // Place the global in the execute-only text section
  95   if (isExecuteOnlyFunction(GO, SK, TM))
  96     SK = SectionKind::getExecuteOnly();
  97
  98   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, SK, TM);
  99 }