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   // 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       .Default(VK_RISCV_Invalid);
124 }
125 
126 StringRef RISCVMCExpr::getVariantKindName(VariantKind Kind) {
127   switch (Kind) {
128   case VK_RISCV_Invalid:
129   case VK_RISCV_None:
130     llvm_unreachable("Invalid ELF symbol kind");
131   case VK_RISCV_LO:
132     return "lo";
133   case VK_RISCV_HI:
134     return "hi";
135   case VK_RISCV_PCREL_LO:
136     return "pcrel_lo";
137   case VK_RISCV_PCREL_HI:
138     return "pcrel_hi";
139   case VK_RISCV_GOT_HI:
140     return "got_pcrel_hi";
141   case VK_RISCV_TPREL_LO:
142     return "tprel_lo";
143   case VK_RISCV_TPREL_HI:
144     return "tprel_hi";
145   case VK_RISCV_TPREL_ADD:
146     return "tprel_add";
147   case VK_RISCV_TLS_GOT_HI:
148     return "tls_ie_pcrel_hi";
149   case VK_RISCV_TLS_GD_HI:
150     return "tls_gd_pcrel_hi";
151   case VK_RISCV_CALL:
152     return "call";
153   case VK_RISCV_CALL_PLT:
154     return "call_plt";
155   case VK_RISCV_32_PCREL:
156     return "32_pcrel";
157   }
158   llvm_unreachable("Invalid ELF symbol kind");
159 }
160 
161 static void fixELFSymbolsInTLSFixupsImpl(const MCExpr *Expr, MCAssembler &Asm) {
162   switch (Expr->getKind()) {
163   case MCExpr::Target:
164     llvm_unreachable("Can't handle nested target expression");
165     break;
166   case MCExpr::Constant:
167     break;
168 
169   case MCExpr::Binary: {
170     const MCBinaryExpr *BE = cast<MCBinaryExpr>(Expr);
171     fixELFSymbolsInTLSFixupsImpl(BE->getLHS(), Asm);
172     fixELFSymbolsInTLSFixupsImpl(BE->getRHS(), Asm);
173     break;
174   }
175 
176   case MCExpr::SymbolRef: {
177     // We're known to be under a TLS fixup, so any symbol should be
178     // modified. There should be only one.
179     const MCSymbolRefExpr &SymRef = *cast<MCSymbolRefExpr>(Expr);
180     cast<MCSymbolELF>(SymRef.getSymbol()).setType(ELF::STT_TLS);
181     break;
182   }
183 
184   case MCExpr::Unary:
185     fixELFSymbolsInTLSFixupsImpl(cast<MCUnaryExpr>(Expr)->getSubExpr(), Asm);
186     break;
187   }
188 }
189 
190 void RISCVMCExpr::fixELFSymbolsInTLSFixups(MCAssembler &Asm) const {
191   switch (getKind()) {
192   default:
193     return;
194   case VK_RISCV_TPREL_HI:
195   case VK_RISCV_TLS_GOT_HI:
196   case VK_RISCV_TLS_GD_HI:
197     break;
198   }
199 
200   fixELFSymbolsInTLSFixupsImpl(getSubExpr(), Asm);
201 }
202 
203 bool RISCVMCExpr::evaluateAsConstant(int64_t &Res) const {
204   MCValue Value;
205 
206   if (Kind == VK_RISCV_PCREL_HI || Kind == VK_RISCV_PCREL_LO ||
207       Kind == VK_RISCV_GOT_HI || Kind == VK_RISCV_TPREL_HI ||
208       Kind == VK_RISCV_TPREL_LO || Kind == VK_RISCV_TPREL_ADD ||
209       Kind == VK_RISCV_TLS_GOT_HI || Kind == VK_RISCV_TLS_GD_HI ||
210       Kind == VK_RISCV_CALL || Kind == VK_RISCV_CALL_PLT)
211     return false;
212 
213   if (!getSubExpr()->evaluateAsRelocatable(Value, nullptr, nullptr))
214     return false;
215 
216   if (!Value.isAbsolute())
217     return false;
218 
219   Res = evaluateAsInt64(Value.getConstant());
220   return true;
221 }
222 
223 int64_t RISCVMCExpr::evaluateAsInt64(int64_t Value) const {
224   switch (Kind) {
225   default:
226     llvm_unreachable("Invalid kind");
227   case VK_RISCV_LO:
228     return SignExtend64<12>(Value);
229   case VK_RISCV_HI:
230     // Add 1 if bit 11 is 1, to compensate for low 12 bits being negative.
231     return ((Value + 0x800) >> 12) & 0xfffff;
232   }
233 }
234