1 //===-- RISCVMCExpr.cpp - RISC-V 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 RISC-V 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/Casting.h"
25 #include "llvm/Support/ErrorHandling.h"
26 
27 using namespace llvm;
28 
29 #define DEBUG_TYPE "riscvmcexpr"
30 
31 const RISCVMCExpr *RISCVMCExpr::create(const MCExpr *Expr, VariantKind Kind,
32                                        MCContext &Ctx) {
33   return new (Ctx) RISCVMCExpr(Expr, Kind);
34 }
35 
36 void RISCVMCExpr::printImpl(raw_ostream &OS, const MCAsmInfo *MAI) const {
37   VariantKind Kind = getKind();
38   bool HasVariant = ((Kind != VK_RISCV_None) && (Kind != VK_RISCV_CALL) &&
39                      (Kind != VK_RISCV_CALL_PLT));
40 
41   if (HasVariant)
42     OS << '%' << getVariantKindName(getKind()) << '(';
43   Expr->print(OS, MAI);
44   if (HasVariant)
45     OS << ')';
46 }
47 
48 const MCFixup *RISCVMCExpr::getPCRelHiFixup(const MCFragment **DFOut) const {
49   MCValue AUIPCLoc;
50   if (!getSubExpr()->evaluateAsRelocatable(AUIPCLoc, nullptr, nullptr))
51     return nullptr;
52 
53   const MCSymbolRefExpr *AUIPCSRE = AUIPCLoc.getSymA();
54   if (!AUIPCSRE)
55     return nullptr;
56 
57   const MCSymbol *AUIPCSymbol = &AUIPCSRE->getSymbol();
58   const auto *DF = dyn_cast_or_null<MCDataFragment>(AUIPCSymbol->getFragment());
59 
60   if (!DF)
61     return nullptr;
62 
63   uint64_t Offset = AUIPCSymbol->getOffset();
64   if (DF->getContents().size() == Offset) {
65     DF = dyn_cast_or_null<MCDataFragment>(DF->getNextNode());
66     if (!DF)
67       return nullptr;
68     Offset = 0;
69   }
70 
71   for (const MCFixup &F : DF->getFixups()) {
72     if (F.getOffset() != Offset)
73       continue;
74 
75     switch ((unsigned)F.getKind()) {
76     default:
77       continue;
78     case RISCV::fixup_riscv_got_hi20:
79     case RISCV::fixup_riscv_tls_got_hi20:
80     case RISCV::fixup_riscv_tls_gd_hi20:
81     case RISCV::fixup_riscv_pcrel_hi20:
82     case RISCV::fixup_riscv_tlsdesc_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   // Explicitly drop the layout and assembler to prevent any symbolic folding in
96   // the expression handling.  This is required to preserve symbolic difference
97   // expressions to emit the paired relocations.
98   if (!getSubExpr()->evaluateAsRelocatable(Res, nullptr, nullptr))
99     return false;
100 
101   Res =
102       MCValue::get(Res.getSymA(), Res.getSymB(), Res.getConstant(), getKind());
103   // Custom fixup types are not valid with symbol difference expressions.
104   return Res.getSymB() ? getKind() == VK_RISCV_None : true;
105 }
106 
107 void RISCVMCExpr::visitUsedExpr(MCStreamer &Streamer) const {
108   Streamer.visitUsedExpr(*getSubExpr());
109 }
110 
111 RISCVMCExpr::VariantKind RISCVMCExpr::getVariantKindForName(StringRef name) {
112   return StringSwitch<RISCVMCExpr::VariantKind>(name)
113       .Case("lo", VK_RISCV_LO)
114       .Case("hi", VK_RISCV_HI)
115       .Case("pcrel_lo", VK_RISCV_PCREL_LO)
116       .Case("pcrel_hi", VK_RISCV_PCREL_HI)
117       .Case("got_pcrel_hi", VK_RISCV_GOT_HI)
118       .Case("tprel_lo", VK_RISCV_TPREL_LO)
119       .Case("tprel_hi", VK_RISCV_TPREL_HI)
120       .Case("tprel_add", VK_RISCV_TPREL_ADD)
121       .Case("tls_ie_pcrel_hi", VK_RISCV_TLS_GOT_HI)
122       .Case("tls_gd_pcrel_hi", VK_RISCV_TLS_GD_HI)
123       .Case("tlsdesc_hi", VK_RISCV_TLSDESC_HI)
124       .Case("tlsdesc_load_lo", VK_RISCV_TLSDESC_LOAD_LO)
125       .Case("tlsdesc_add_lo", VK_RISCV_TLSDESC_ADD_LO)
126       .Case("tlsdesc_call", VK_RISCV_TLSDESC_CALL)
127       .Default(VK_RISCV_Invalid);
128 }
129 
130 StringRef RISCVMCExpr::getVariantKindName(VariantKind Kind) {
131   switch (Kind) {
132   case VK_RISCV_Invalid:
133   case VK_RISCV_None:
134     llvm_unreachable("Invalid ELF symbol kind");
135   case VK_RISCV_LO:
136     return "lo";
137   case VK_RISCV_HI:
138     return "hi";
139   case VK_RISCV_PCREL_LO:
140     return "pcrel_lo";
141   case VK_RISCV_PCREL_HI:
142     return "pcrel_hi";
143   case VK_RISCV_GOT_HI:
144     return "got_pcrel_hi";
145   case VK_RISCV_TPREL_LO:
146     return "tprel_lo";
147   case VK_RISCV_TPREL_HI:
148     return "tprel_hi";
149   case VK_RISCV_TPREL_ADD:
150     return "tprel_add";
151   case VK_RISCV_TLS_GOT_HI:
152     return "tls_ie_pcrel_hi";
153   case VK_RISCV_TLSDESC_HI:
154     return "tlsdesc_hi";
155   case VK_RISCV_TLSDESC_LOAD_LO:
156     return "tlsdesc_load_lo";
157   case VK_RISCV_TLSDESC_ADD_LO:
158     return "tlsdesc_add_lo";
159   case VK_RISCV_TLSDESC_CALL:
160     return "tlsdesc_call";
161   case VK_RISCV_TLS_GD_HI:
162     return "tls_gd_pcrel_hi";
163   case VK_RISCV_CALL:
164     return "call";
165   case VK_RISCV_CALL_PLT:
166     return "call_plt";
167   case VK_RISCV_32_PCREL:
168     return "32_pcrel";
169   }
170   llvm_unreachable("Invalid ELF symbol kind");
171 }
172 
173 static void fixELFSymbolsInTLSFixupsImpl(const MCExpr *Expr, MCAssembler &Asm) {
174   switch (Expr->getKind()) {
175   case MCExpr::Target:
176     llvm_unreachable("Can't handle nested target expression");
177     break;
178   case MCExpr::Constant:
179     break;
180 
181   case MCExpr::Binary: {
182     const MCBinaryExpr *BE = cast<MCBinaryExpr>(Expr);
183     fixELFSymbolsInTLSFixupsImpl(BE->getLHS(), Asm);
184     fixELFSymbolsInTLSFixupsImpl(BE->getRHS(), Asm);
185     break;
186   }
187 
188   case MCExpr::SymbolRef: {
189     // We're known to be under a TLS fixup, so any symbol should be
190     // modified. There should be only one.
191     const MCSymbolRefExpr &SymRef = *cast<MCSymbolRefExpr>(Expr);
192     cast<MCSymbolELF>(SymRef.getSymbol()).setType(ELF::STT_TLS);
193     break;
194   }
195 
196   case MCExpr::Unary:
197     fixELFSymbolsInTLSFixupsImpl(cast<MCUnaryExpr>(Expr)->getSubExpr(), Asm);
198     break;
199   }
200 }
201 
202 void RISCVMCExpr::fixELFSymbolsInTLSFixups(MCAssembler &Asm) const {
203   switch (getKind()) {
204   default:
205     return;
206   case VK_RISCV_TPREL_HI:
207   case VK_RISCV_TLS_GOT_HI:
208   case VK_RISCV_TLS_GD_HI:
209   case VK_RISCV_TLSDESC_HI:
210   case VK_RISCV_TLSDESC_ADD_LO:
211   case VK_RISCV_TLSDESC_LOAD_LO:
212     break;
213   }
214 
215   fixELFSymbolsInTLSFixupsImpl(getSubExpr(), Asm);
216 }
217 
218 bool RISCVMCExpr::evaluateAsConstant(int64_t &Res) const {
219   MCValue Value;
220 
221   if (Kind == VK_RISCV_PCREL_HI || Kind == VK_RISCV_PCREL_LO ||
222       Kind == VK_RISCV_GOT_HI || Kind == VK_RISCV_TPREL_HI ||
223       Kind == VK_RISCV_TPREL_LO || Kind == VK_RISCV_TPREL_ADD ||
224       Kind == VK_RISCV_TLS_GOT_HI || Kind == VK_RISCV_TLS_GD_HI ||
225       Kind == VK_RISCV_TLSDESC_HI || Kind == VK_RISCV_TLSDESC_LOAD_LO ||
226       Kind == VK_RISCV_TLSDESC_ADD_LO || Kind == VK_RISCV_TLSDESC_CALL ||
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