1 //===-- SystemZMCObjectWriter.cpp - SystemZ ELF writer --------------------===//
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 "MCTargetDesc/SystemZMCTargetDesc.h"
11 #include "MCTargetDesc/SystemZMCFixups.h"
12 #include "llvm/MC/MCELFObjectWriter.h"
13 #include "llvm/MC/MCExpr.h"
14 #include "llvm/MC/MCValue.h"
15 
16 using namespace llvm;
17 
18 namespace {
19 class SystemZObjectWriter : public MCELFObjectTargetWriter {
20 public:
21   SystemZObjectWriter(uint8_t OSABI);
22 
23   ~SystemZObjectWriter() override;
24 
25 protected:
26   // Override MCELFObjectTargetWriter.
27   unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
28                         bool IsPCRel) const override;
29   void sortRelocs(const MCAssembler &Asm,
30                   std::vector<ELFRelocationEntry> &Relocs) override;
31 };
32 } // end anonymous namespace
33 
34 SystemZObjectWriter::SystemZObjectWriter(uint8_t OSABI)
35   : MCELFObjectTargetWriter(/*Is64Bit=*/true, OSABI, ELF::EM_S390,
36                             /*HasRelocationAddend=*/ true) {}
37 
38 SystemZObjectWriter::~SystemZObjectWriter() {
39 }
40 
41 // Return the relocation type for an absolute value of MCFixupKind Kind.
42 static unsigned getAbsoluteReloc(unsigned Kind) {
43   switch (Kind) {
44   case FK_Data_1: return ELF::R_390_8;
45   case FK_Data_2: return ELF::R_390_16;
46   case FK_Data_4: return ELF::R_390_32;
47   case FK_Data_8: return ELF::R_390_64;
48   }
49   llvm_unreachable("Unsupported absolute address");
50 }
51 
52 // Return the relocation type for a PC-relative value of MCFixupKind Kind.
53 static unsigned getPCRelReloc(unsigned Kind) {
54   switch (Kind) {
55   case FK_Data_2:                return ELF::R_390_PC16;
56   case FK_Data_4:                return ELF::R_390_PC32;
57   case FK_Data_8:                return ELF::R_390_PC64;
58   case SystemZ::FK_390_PC16DBL:  return ELF::R_390_PC16DBL;
59   case SystemZ::FK_390_PC32DBL:  return ELF::R_390_PC32DBL;
60   }
61   llvm_unreachable("Unsupported PC-relative address");
62 }
63 
64 // Return the R_390_TLS_LE* relocation type for MCFixupKind Kind.
65 static unsigned getTLSLEReloc(unsigned Kind) {
66   switch (Kind) {
67   case FK_Data_4: return ELF::R_390_TLS_LE32;
68   case FK_Data_8: return ELF::R_390_TLS_LE64;
69   }
70   llvm_unreachable("Unsupported absolute address");
71 }
72 
73 // Return the R_390_TLS_LDO* relocation type for MCFixupKind Kind.
74 static unsigned getTLSLDOReloc(unsigned Kind) {
75   switch (Kind) {
76   case FK_Data_4: return ELF::R_390_TLS_LDO32;
77   case FK_Data_8: return ELF::R_390_TLS_LDO64;
78   }
79   llvm_unreachable("Unsupported absolute address");
80 }
81 
82 // Return the R_390_TLS_LDM* relocation type for MCFixupKind Kind.
83 static unsigned getTLSLDMReloc(unsigned Kind) {
84   switch (Kind) {
85   case FK_Data_4: return ELF::R_390_TLS_LDM32;
86   case FK_Data_8: return ELF::R_390_TLS_LDM64;
87   case SystemZ::FK_390_TLS_CALL: return ELF::R_390_TLS_LDCALL;
88   }
89   llvm_unreachable("Unsupported absolute address");
90 }
91 
92 // Return the R_390_TLS_GD* relocation type for MCFixupKind Kind.
93 static unsigned getTLSGDReloc(unsigned Kind) {
94   switch (Kind) {
95   case FK_Data_4: return ELF::R_390_TLS_GD32;
96   case FK_Data_8: return ELF::R_390_TLS_GD64;
97   case SystemZ::FK_390_TLS_CALL: return ELF::R_390_TLS_GDCALL;
98   }
99   llvm_unreachable("Unsupported absolute address");
100 }
101 
102 // Return the PLT relocation counterpart of MCFixupKind Kind.
103 static unsigned getPLTReloc(unsigned Kind) {
104   switch (Kind) {
105   case SystemZ::FK_390_PC16DBL: return ELF::R_390_PLT16DBL;
106   case SystemZ::FK_390_PC32DBL: return ELF::R_390_PLT32DBL;
107   }
108   llvm_unreachable("Unsupported absolute address");
109 }
110 
111 unsigned SystemZObjectWriter::GetRelocType(const MCValue &Target,
112                                            const MCFixup &Fixup,
113                                            bool IsPCRel) const {
114   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
115   unsigned Kind = Fixup.getKind();
116   switch (Modifier) {
117   case MCSymbolRefExpr::VK_None:
118     if (IsPCRel)
119       return getPCRelReloc(Kind);
120     return getAbsoluteReloc(Kind);
121 
122   case MCSymbolRefExpr::VK_NTPOFF:
123     assert(!IsPCRel && "NTPOFF shouldn't be PC-relative");
124     return getTLSLEReloc(Kind);
125 
126   case MCSymbolRefExpr::VK_INDNTPOFF:
127     if (IsPCRel && Kind == SystemZ::FK_390_PC32DBL)
128       return ELF::R_390_TLS_IEENT;
129     llvm_unreachable("Only PC-relative INDNTPOFF accesses are supported for now");
130 
131   case MCSymbolRefExpr::VK_DTPOFF:
132     assert(!IsPCRel && "DTPOFF shouldn't be PC-relative");
133     return getTLSLDOReloc(Kind);
134 
135   case MCSymbolRefExpr::VK_TLSLDM:
136     assert(!IsPCRel && "TLSLDM shouldn't be PC-relative");
137     return getTLSLDMReloc(Kind);
138 
139   case MCSymbolRefExpr::VK_TLSGD:
140     assert(!IsPCRel && "TLSGD shouldn't be PC-relative");
141     return getTLSGDReloc(Kind);
142 
143   case MCSymbolRefExpr::VK_GOT:
144     if (IsPCRel && Kind == SystemZ::FK_390_PC32DBL)
145       return ELF::R_390_GOTENT;
146     llvm_unreachable("Only PC-relative GOT accesses are supported for now");
147 
148   case MCSymbolRefExpr::VK_PLT:
149     assert(IsPCRel && "@PLT shouldt be PC-relative");
150     return getPLTReloc(Kind);
151 
152   default:
153     llvm_unreachable("Modifier not supported");
154   }
155 }
156 
157 void SystemZObjectWriter::sortRelocs(const MCAssembler &Asm,
158                                      std::vector<ELFRelocationEntry> &Relocs) {
159   // The default function sorts entries by Offset in descending order.
160   MCELFObjectTargetWriter::sortRelocs(Asm, Relocs);
161 
162   // This is OK for SystemZ, except for R_390_TLS_GDCALL/LDCALL relocs.
163   // There is typically another reloc, a R_390_PLT32DBL, on the same
164   // instruction.  This other reloc must come *before* the GDCALL reloc,
165   // or else the TLS linker optimization may generate incorrect code.
166   for (unsigned i = 0, e = Relocs.size(); i + 1 < e; ++i) {
167     if ((Relocs[i + 1].Type == ELF::R_390_TLS_GDCALL ||
168          Relocs[i + 1].Type == ELF::R_390_TLS_LDCALL) &&
169         Relocs[i].Offset == Relocs[i + 1].Offset + 2)
170       std::swap(Relocs[i], Relocs[i + 1]);
171   }
172 }
173 
174 MCObjectWriter *llvm::createSystemZObjectWriter(raw_pwrite_stream &OS,
175                                                 uint8_t OSABI) {
176   MCELFObjectTargetWriter *MOTW = new SystemZObjectWriter(OSABI);
177   return createELFObjectWriter(MOTW, OS, /*IsLittleEndian=*/false);
178 }
179