1 //===-- CodeGen/AsmPrinter/DwarfException.cpp - Dwarf Exception 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 // This file contains support for writing DWARF exception info into asm files.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "DwarfException.h"
15 #include "llvm/ADT/StringExtras.h"
16 #include "llvm/ADT/Twine.h"
17 #include "llvm/CodeGen/AsmPrinter.h"
18 #include "llvm/CodeGen/MachineFrameInfo.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/MachineModuleInfo.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/Mangler.h"
23 #include "llvm/IR/Module.h"
24 #include "llvm/MC/MCAsmInfo.h"
25 #include "llvm/MC/MCContext.h"
26 #include "llvm/MC/MCExpr.h"
27 #include "llvm/MC/MCSection.h"
28 #include "llvm/MC/MCStreamer.h"
29 #include "llvm/MC/MCSymbol.h"
30 #include "llvm/MC/MachineLocation.h"
31 #include "llvm/Support/Dwarf.h"
32 #include "llvm/Support/ErrorHandling.h"
33 #include "llvm/Support/FormattedStream.h"
34 #include "llvm/Target/TargetFrameLowering.h"
35 #include "llvm/Target/TargetLoweringObjectFile.h"
36 #include "llvm/Target/TargetMachine.h"
37 #include "llvm/Target/TargetOptions.h"
38 #include "llvm/Target/TargetRegisterInfo.h"
39 using namespace llvm;
40 
41 DwarfCFIExceptionBase::DwarfCFIExceptionBase(AsmPrinter *A)
42     : EHStreamer(A), shouldEmitCFI(false) {}
43 
44 void DwarfCFIExceptionBase::markFunctionEnd() {
45   endFragment();
46 
47   if (MMI->getLandingPads().empty())
48     return;
49 
50   // Map all labels and get rid of any dead landing pads.
51   MMI->TidyLandingPads();
52 }
53 
54 void DwarfCFIExceptionBase::endFragment() {
55   if (shouldEmitCFI)
56     Asm->OutStreamer->EmitCFIEndProc();
57 }
58 
59 DwarfCFIException::DwarfCFIException(AsmPrinter *A)
60     : DwarfCFIExceptionBase(A), shouldEmitPersonality(false),
61       forceEmitPersonality(false), shouldEmitLSDA(false),
62       shouldEmitMoves(false), moveTypeModule(AsmPrinter::CFI_M_None) {}
63 
64 DwarfCFIException::~DwarfCFIException() {}
65 
66 /// endModule - Emit all exception information that should come after the
67 /// content.
68 void DwarfCFIException::endModule() {
69   // SjLj uses this pass and it doesn't need this info.
70   if (!Asm->MAI->usesCFIForEH())
71     return;
72 
73   if (moveTypeModule == AsmPrinter::CFI_M_Debug)
74     Asm->OutStreamer->EmitCFISections(false, true);
75 
76   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
77 
78   unsigned PerEncoding = TLOF.getPersonalityEncoding();
79 
80   if ((PerEncoding & 0x80) != dwarf::DW_EH_PE_indirect)
81     return;
82 
83   // Emit references to all used personality functions
84   for (const Function *Personality : MMI->getPersonalities()) {
85     if (!Personality)
86       continue;
87     MCSymbol *Sym = Asm->getSymbol(Personality);
88     TLOF.emitPersonalityValue(*Asm->OutStreamer, Asm->getDataLayout(), Sym);
89   }
90 }
91 
92 static MCSymbol *getExceptionSym(AsmPrinter *Asm) {
93   return Asm->getCurExceptionSym();
94 }
95 
96 void DwarfCFIException::beginFunction(const MachineFunction *MF) {
97   shouldEmitMoves = shouldEmitPersonality = shouldEmitLSDA = false;
98   const Function *F = MF->getFunction();
99 
100   // If any landing pads survive, we need an EH table.
101   bool hasLandingPads = !MMI->getLandingPads().empty();
102 
103   // See if we need frame move info.
104   AsmPrinter::CFIMoveType MoveType = Asm->needsCFIMoves();
105   if (MoveType == AsmPrinter::CFI_M_EH ||
106       (MoveType == AsmPrinter::CFI_M_Debug &&
107        moveTypeModule == AsmPrinter::CFI_M_None))
108     moveTypeModule = MoveType;
109 
110   shouldEmitMoves = MoveType != AsmPrinter::CFI_M_None;
111 
112   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
113   unsigned PerEncoding = TLOF.getPersonalityEncoding();
114   const Function *Per = nullptr;
115   if (F->hasPersonalityFn())
116     Per = dyn_cast<Function>(F->getPersonalityFn()->stripPointerCasts());
117 
118   // Emit a personality function even when there are no landing pads
119   forceEmitPersonality =
120       // ...if a personality function is explicitly specified
121       F->hasPersonalityFn() &&
122       // ... and it's not known to be a noop in the absence of invokes
123       !isNoOpWithoutInvoke(classifyEHPersonality(Per)) &&
124       // ... and we're not explicitly asked not to emit it
125       F->needsUnwindTableEntry();
126 
127   shouldEmitPersonality =
128       (forceEmitPersonality ||
129        (hasLandingPads && PerEncoding != dwarf::DW_EH_PE_omit)) &&
130       Per;
131 
132   unsigned LSDAEncoding = TLOF.getLSDAEncoding();
133   shouldEmitLSDA = shouldEmitPersonality &&
134     LSDAEncoding != dwarf::DW_EH_PE_omit;
135 
136   shouldEmitCFI = MF->getMMI().getContext().getAsmInfo()->usesCFIForEH() &&
137                   (shouldEmitPersonality || shouldEmitMoves);
138   beginFragment(&*MF->begin(), getExceptionSym);
139 }
140 
141 void DwarfCFIException::beginFragment(const MachineBasicBlock *MBB,
142                                       ExceptionSymbolProvider ESP) {
143   if (!shouldEmitCFI)
144     return;
145 
146   Asm->OutStreamer->EmitCFIStartProc(/*IsSimple=*/false);
147 
148   // Indicate personality routine, if any.
149   if (!shouldEmitPersonality)
150     return;
151 
152   auto *F = MBB->getParent()->getFunction();
153   auto *P = dyn_cast<Function>(F->getPersonalityFn()->stripPointerCasts());
154   assert(P && "Expected personality function");
155 
156   // If we are forced to emit this personality, make sure to record
157   // it because it might not appear in any landingpad
158   if (forceEmitPersonality)
159     MMI->addPersonality(P);
160 
161   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
162   unsigned PerEncoding = TLOF.getPersonalityEncoding();
163   const MCSymbol *Sym = TLOF.getCFIPersonalitySymbol(P, Asm->TM, MMI);
164   Asm->OutStreamer->EmitCFIPersonality(Sym, PerEncoding);
165 
166   // Provide LSDA information.
167   if (shouldEmitLSDA)
168     Asm->OutStreamer->EmitCFILsda(ESP(Asm), TLOF.getLSDAEncoding());
169 }
170 
171 /// endFunction - Gather and emit post-function exception information.
172 ///
173 void DwarfCFIException::endFunction(const MachineFunction *) {
174   if (!shouldEmitPersonality)
175     return;
176 
177   emitExceptionTable();
178 }
179