1 //===-- llvm/Target/ARMTargetObjectFile.cpp - ARM Object Info Impl --------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "ARMTargetObjectFile.h"
11 #include "ARMSubtarget.h"
12 #include "ARMTargetMachine.h"
13 #include "llvm/BinaryFormat/Dwarf.h"
14 #include "llvm/BinaryFormat/ELF.h"
15 #include "llvm/MC/MCAsmInfo.h"
16 #include "llvm/MC/MCContext.h"
17 #include "llvm/MC/MCExpr.h"
18 #include "llvm/MC/MCSectionELF.h"
19 #include "llvm/MC/MCTargetOptions.h"
20 #include "llvm/MC/SectionKind.h"
21 #include "llvm/Target/TargetMachine.h"
22 #include <cassert>
23 
24 using namespace llvm;
25 using namespace dwarf;
26 
27 //===----------------------------------------------------------------------===//
28 //                               ELF Target
29 //===----------------------------------------------------------------------===//
30 
31 void ARMElfTargetObjectFile::Initialize(MCContext &Ctx,
32                                         const TargetMachine &TM) {
33   const ARMBaseTargetMachine &ARM_TM = static_cast<const ARMBaseTargetMachine &>(TM);
34   bool isAAPCS_ABI = ARM_TM.TargetABI == ARMBaseTargetMachine::ARMABI::ARM_ABI_AAPCS;
35   bool genExecuteOnly =
36       ARM_TM.getMCSubtargetInfo()->hasFeature(ARM::FeatureExecuteOnly);
37 
38   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
39   InitializeELF(isAAPCS_ABI);
40 
41   if (isAAPCS_ABI) {
42     LSDASection = nullptr;
43   }
44 
45   // Make code section unreadable when in execute-only mode
46   if (genExecuteOnly) {
47     unsigned Type = ELF::SHT_PROGBITS;
48     unsigned Flags =
49         ELF::SHF_EXECINSTR | ELF::SHF_ALLOC | ELF::SHF_ARM_PURECODE;
50     // Since we cannot modify flags for an existing section, we create a new
51     // section with the right flags, and use 0 as the unique ID for
52     // execute-only text
53     TextSection = Ctx.getELFSection(".text", Type, Flags, 0, "", 0U);
54   }
55 }
56 
57 const MCExpr *ARMElfTargetObjectFile::getTTypeGlobalReference(
58     const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
59     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
60   if (TM.getMCAsmInfo()->getExceptionHandlingType() != ExceptionHandling::ARM)
61     return TargetLoweringObjectFileELF::getTTypeGlobalReference(
62         GV, Encoding, TM, MMI, Streamer);
63 
64   assert(Encoding == DW_EH_PE_absptr && "Can handle absptr encoding only");
65 
66   return MCSymbolRefExpr::create(TM.getSymbol(GV),
67                                  MCSymbolRefExpr::VK_ARM_TARGET2, getContext());
68 }
69 
70 const MCExpr *ARMElfTargetObjectFile::
71 getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
72   return MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_ARM_TLSLDO,
73                                  getContext());
74 }
75 
76 static bool isExecuteOnlyFunction(const GlobalObject *GO, SectionKind SK,
77                                   const TargetMachine &TM) {
78   if (const Function *F = dyn_cast<Function>(GO))
79     if (TM.getSubtarget<ARMSubtarget>(*F).genExecuteOnly() && SK.isText())
80       return true;
81   return false;
82 }
83 
84 MCSection *ARMElfTargetObjectFile::getExplicitSectionGlobal(
85     const GlobalObject *GO, SectionKind SK, const TargetMachine &TM) const {
86   // Set execute-only access for the explicit section
87   if (isExecuteOnlyFunction(GO, SK, TM))
88     SK = SectionKind::getExecuteOnly();
89 
90   return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, SK, TM);
91 }
92 
93 MCSection *ARMElfTargetObjectFile::SelectSectionForGlobal(
94     const GlobalObject *GO, SectionKind SK, const TargetMachine &TM) const {
95   // Place the global in the execute-only text section
96   if (isExecuteOnlyFunction(GO, SK, TM))
97     SK = SectionKind::getExecuteOnly();
98 
99   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, SK, TM);
100 }
101