1 //===-- RISCVMCExpr.cpp - RISCV specific MC expression classes ------------===//
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 // This file contains the implementation of the assembly expression modifiers
10 // accepted by the RISCV architecture (e.g. ":lo12:", ":gottprel_g1:", ...).
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "RISCVMCExpr.h"
15 #include "MCTargetDesc/RISCVAsmBackend.h"
16 #include "RISCVFixupKinds.h"
17 #include "llvm/BinaryFormat/ELF.h"
18 #include "llvm/MC/MCAsmLayout.h"
19 #include "llvm/MC/MCAssembler.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCStreamer.h"
22 #include "llvm/MC/MCSymbolELF.h"
23 #include "llvm/MC/MCValue.h"
24 #include "llvm/Support/ErrorHandling.h"
25 
26 using namespace llvm;
27 
28 #define DEBUG_TYPE "riscvmcexpr"
29 
30 const RISCVMCExpr *RISCVMCExpr::create(const MCExpr *Expr, VariantKind Kind,
31                                        MCContext &Ctx) {
32   return new (Ctx) RISCVMCExpr(Expr, Kind);
33 }
34 
35 void RISCVMCExpr::printImpl(raw_ostream &OS, const MCAsmInfo *MAI) const {
36   VariantKind Kind = getKind();
37   bool HasVariant = ((Kind != VK_RISCV_None) && (Kind != VK_RISCV_CALL) &&
38                      (Kind != VK_RISCV_CALL_PLT));
39 
40   if (HasVariant)
41     OS << '%' << getVariantKindName(getKind()) << '(';
42   Expr->print(OS, MAI);
43   if (Kind == VK_RISCV_CALL_PLT)
44     OS << "@plt";
45   if (HasVariant)
46     OS << ')';
47 }
48 
49 const MCFixup *RISCVMCExpr::getPCRelHiFixup(const MCFragment **DFOut) const {
50   MCValue AUIPCLoc;
51   if (!getSubExpr()->evaluateAsRelocatable(AUIPCLoc, nullptr, nullptr))
52     return nullptr;
53 
54   const MCSymbolRefExpr *AUIPCSRE = AUIPCLoc.getSymA();
55   if (!AUIPCSRE)
56     return nullptr;
57 
58   const MCSymbol *AUIPCSymbol = &AUIPCSRE->getSymbol();
59   const auto *DF = dyn_cast_or_null<MCDataFragment>(AUIPCSymbol->getFragment());
60 
61   if (!DF)
62     return nullptr;
63 
64   uint64_t Offset = AUIPCSymbol->getOffset();
65   if (DF->getContents().size() == Offset) {
66     DF = dyn_cast_or_null<MCDataFragment>(DF->getNextNode());
67     if (!DF)
68       return nullptr;
69     Offset = 0;
70   }
71 
72   for (const MCFixup &F : DF->getFixups()) {
73     if (F.getOffset() != Offset)
74       continue;
75 
76     switch ((unsigned)F.getKind()) {
77     default:
78       continue;
79     case RISCV::fixup_riscv_got_hi20:
80     case RISCV::fixup_riscv_tls_got_hi20:
81     case RISCV::fixup_riscv_tls_gd_hi20:
82     case RISCV::fixup_riscv_pcrel_hi20:
83       if (DFOut)
84         *DFOut = DF;
85       return &F;
86     }
87   }
88 
89   return nullptr;
90 }
91 
92 bool RISCVMCExpr::evaluateAsRelocatableImpl(MCValue &Res,
93                                             const MCAsmLayout *Layout,
94                                             const MCFixup *Fixup) const {
95   bool IsSymbolicDifference = false;
96   if (const auto *MBE = dyn_cast<MCBinaryExpr>(getSubExpr())) {
97     if (isa<MCBinaryExpr>(MBE->getLHS()) && isa<MCConstantExpr>(MBE->getRHS()))
98       MBE = cast<MCBinaryExpr>(MBE->getLHS());
99     IsSymbolicDifference = isa<MCSymbolRefExpr>(MBE->getLHS()) &&
100                            isa<MCSymbolRefExpr>(MBE->getRHS());
101   }
102 
103   // Some custom fixup types are not valid with symbol difference expressions
104   if (IsSymbolicDifference) {
105     switch (getKind()) {
106     default:
107       break;
108     case VK_RISCV_LO:
109     case VK_RISCV_HI:
110     case VK_RISCV_PCREL_LO:
111     case VK_RISCV_PCREL_HI:
112     case VK_RISCV_GOT_HI:
113     case VK_RISCV_TPREL_LO:
114     case VK_RISCV_TPREL_HI:
115     case VK_RISCV_TPREL_ADD:
116     case VK_RISCV_TLS_GOT_HI:
117     case VK_RISCV_TLS_GD_HI:
118       return false;
119     }
120   }
121   return getSubExpr()->evaluateAsRelocatable(Res, Layout, Fixup);
122 }
123 
124 void RISCVMCExpr::visitUsedExpr(MCStreamer &Streamer) const {
125   Streamer.visitUsedExpr(*getSubExpr());
126 }
127 
128 RISCVMCExpr::VariantKind RISCVMCExpr::getVariantKindForName(StringRef name) {
129   return StringSwitch<RISCVMCExpr::VariantKind>(name)
130       .Case("lo", VK_RISCV_LO)
131       .Case("hi", VK_RISCV_HI)
132       .Case("pcrel_lo", VK_RISCV_PCREL_LO)
133       .Case("pcrel_hi", VK_RISCV_PCREL_HI)
134       .Case("got_pcrel_hi", VK_RISCV_GOT_HI)
135       .Case("tprel_lo", VK_RISCV_TPREL_LO)
136       .Case("tprel_hi", VK_RISCV_TPREL_HI)
137       .Case("tprel_add", VK_RISCV_TPREL_ADD)
138       .Case("tls_ie_pcrel_hi", VK_RISCV_TLS_GOT_HI)
139       .Case("tls_gd_pcrel_hi", VK_RISCV_TLS_GD_HI)
140       .Default(VK_RISCV_Invalid);
141 }
142 
143 StringRef RISCVMCExpr::getVariantKindName(VariantKind Kind) {
144   switch (Kind) {
145   case VK_RISCV_Invalid:
146   case VK_RISCV_None:
147     llvm_unreachable("Invalid ELF symbol kind");
148   case VK_RISCV_LO:
149     return "lo";
150   case VK_RISCV_HI:
151     return "hi";
152   case VK_RISCV_PCREL_LO:
153     return "pcrel_lo";
154   case VK_RISCV_PCREL_HI:
155     return "pcrel_hi";
156   case VK_RISCV_GOT_HI:
157     return "got_pcrel_hi";
158   case VK_RISCV_TPREL_LO:
159     return "tprel_lo";
160   case VK_RISCV_TPREL_HI:
161     return "tprel_hi";
162   case VK_RISCV_TPREL_ADD:
163     return "tprel_add";
164   case VK_RISCV_TLS_GOT_HI:
165     return "tls_ie_pcrel_hi";
166   case VK_RISCV_TLS_GD_HI:
167     return "tls_gd_pcrel_hi";
168   case VK_RISCV_CALL:
169     return "call";
170   case VK_RISCV_CALL_PLT:
171     return "call_plt";
172   case VK_RISCV_32_PCREL:
173     return "32_pcrel";
174   }
175   llvm_unreachable("Invalid ELF symbol kind");
176 }
177 
178 static void fixELFSymbolsInTLSFixupsImpl(const MCExpr *Expr, MCAssembler &Asm) {
179   switch (Expr->getKind()) {
180   case MCExpr::Target:
181     llvm_unreachable("Can't handle nested target expression");
182     break;
183   case MCExpr::Constant:
184     break;
185 
186   case MCExpr::Binary: {
187     const MCBinaryExpr *BE = cast<MCBinaryExpr>(Expr);
188     fixELFSymbolsInTLSFixupsImpl(BE->getLHS(), Asm);
189     fixELFSymbolsInTLSFixupsImpl(BE->getRHS(), Asm);
190     break;
191   }
192 
193   case MCExpr::SymbolRef: {
194     // We're known to be under a TLS fixup, so any symbol should be
195     // modified. There should be only one.
196     const MCSymbolRefExpr &SymRef = *cast<MCSymbolRefExpr>(Expr);
197     cast<MCSymbolELF>(SymRef.getSymbol()).setType(ELF::STT_TLS);
198     break;
199   }
200 
201   case MCExpr::Unary:
202     fixELFSymbolsInTLSFixupsImpl(cast<MCUnaryExpr>(Expr)->getSubExpr(), Asm);
203     break;
204   }
205 }
206 
207 void RISCVMCExpr::fixELFSymbolsInTLSFixups(MCAssembler &Asm) const {
208   switch (getKind()) {
209   default:
210     return;
211   case VK_RISCV_TPREL_HI:
212   case VK_RISCV_TLS_GOT_HI:
213   case VK_RISCV_TLS_GD_HI:
214     break;
215   }
216 
217   fixELFSymbolsInTLSFixupsImpl(getSubExpr(), Asm);
218 }
219 
220 bool RISCVMCExpr::evaluateAsConstant(int64_t &Res) const {
221   MCValue Value;
222 
223   if (Kind == VK_RISCV_PCREL_HI || Kind == VK_RISCV_PCREL_LO ||
224       Kind == VK_RISCV_GOT_HI || Kind == VK_RISCV_TPREL_HI ||
225       Kind == VK_RISCV_TPREL_LO || Kind == VK_RISCV_TPREL_ADD ||
226       Kind == VK_RISCV_TLS_GOT_HI || Kind == VK_RISCV_TLS_GD_HI ||
227       Kind == VK_RISCV_CALL || Kind == VK_RISCV_CALL_PLT)
228     return false;
229 
230   if (!getSubExpr()->evaluateAsRelocatable(Value, nullptr, nullptr))
231     return false;
232 
233   if (!Value.isAbsolute())
234     return false;
235 
236   Res = evaluateAsInt64(Value.getConstant());
237   return true;
238 }
239 
240 int64_t RISCVMCExpr::evaluateAsInt64(int64_t Value) const {
241   switch (Kind) {
242   default:
243     llvm_unreachable("Invalid kind");
244   case VK_RISCV_LO:
245     return SignExtend64<12>(Value);
246   case VK_RISCV_HI:
247     // Add 1 if bit 11 is 1, to compensate for low 12 bits being negative.
248     return ((Value + 0x800) >> 12) & 0xfffff;
249   }
250 }
251