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/BinaryFormat/Dwarf.h"
18 #include "llvm/CodeGen/AsmPrinter.h"
19 #include "llvm/CodeGen/MachineFrameInfo.h"
20 #include "llvm/CodeGen/MachineFunction.h"
21 #include "llvm/CodeGen/MachineModuleInfo.h"
22 #include "llvm/IR/DataLayout.h"
23 #include "llvm/IR/Mangler.h"
24 #include "llvm/IR/Module.h"
25 #include "llvm/MC/MCAsmInfo.h"
26 #include "llvm/MC/MCContext.h"
27 #include "llvm/MC/MCExpr.h"
28 #include "llvm/MC/MCSection.h"
29 #include "llvm/MC/MCStreamer.h"
30 #include "llvm/MC/MCSymbol.h"
31 #include "llvm/MC/MachineLocation.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), hasEmittedCFISections(false) {}
43 
44 void DwarfCFIExceptionBase::markFunctionEnd() {
45   endFragment();
46 
47   // Map all labels and get rid of any dead landing pads.
48   if (!Asm->MF->getLandingPads().empty()) {
49     MachineFunction *NonConstMF = const_cast<MachineFunction*>(Asm->MF);
50     NonConstMF->tidyLandingPads();
51   }
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) {}
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   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
74 
75   unsigned PerEncoding = TLOF.getPersonalityEncoding();
76 
77   if ((PerEncoding & 0x80) != dwarf::DW_EH_PE_indirect)
78     return;
79 
80   // Emit references to all used personality functions
81   for (const Function *Personality : MMI->getPersonalities()) {
82     if (!Personality)
83       continue;
84     MCSymbol *Sym = Asm->getSymbol(Personality);
85     TLOF.emitPersonalityValue(*Asm->OutStreamer, Asm->getDataLayout(), Sym);
86   }
87 }
88 
89 static MCSymbol *getExceptionSym(AsmPrinter *Asm) {
90   return Asm->getCurExceptionSym();
91 }
92 
93 void DwarfCFIException::beginFunction(const MachineFunction *MF) {
94   shouldEmitMoves = shouldEmitPersonality = shouldEmitLSDA = false;
95   const Function *F = MF->getFunction();
96 
97   // If any landing pads survive, we need an EH table.
98   bool hasLandingPads = !MF->getLandingPads().empty();
99 
100   // See if we need frame move info.
101   AsmPrinter::CFIMoveType MoveType = Asm->needsCFIMoves();
102 
103   shouldEmitMoves = MoveType != AsmPrinter::CFI_M_None;
104 
105   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
106   unsigned PerEncoding = TLOF.getPersonalityEncoding();
107   const Function *Per = nullptr;
108   if (F->hasPersonalityFn())
109     Per = dyn_cast<Function>(F->getPersonalityFn()->stripPointerCasts());
110 
111   // Emit a personality function even when there are no landing pads
112   forceEmitPersonality =
113       // ...if a personality function is explicitly specified
114       F->hasPersonalityFn() &&
115       // ... and it's not known to be a noop in the absence of invokes
116       !isNoOpWithoutInvoke(classifyEHPersonality(Per)) &&
117       // ... and we're not explicitly asked not to emit it
118       F->needsUnwindTableEntry();
119 
120   shouldEmitPersonality =
121       (forceEmitPersonality ||
122        (hasLandingPads && PerEncoding != dwarf::DW_EH_PE_omit)) &&
123       Per;
124 
125   unsigned LSDAEncoding = TLOF.getLSDAEncoding();
126   shouldEmitLSDA = shouldEmitPersonality &&
127     LSDAEncoding != dwarf::DW_EH_PE_omit;
128 
129   shouldEmitCFI = MF->getMMI().getContext().getAsmInfo()->usesCFIForEH() &&
130                   (shouldEmitPersonality || shouldEmitMoves);
131   beginFragment(&*MF->begin(), getExceptionSym);
132 }
133 
134 void DwarfCFIException::beginFragment(const MachineBasicBlock *MBB,
135                                       ExceptionSymbolProvider ESP) {
136   if (!shouldEmitCFI)
137     return;
138 
139   if (!hasEmittedCFISections) {
140     if (Asm->needsOnlyDebugCFIMoves())
141       Asm->OutStreamer->EmitCFISections(false, true);
142     hasEmittedCFISections = true;
143   }
144 
145   Asm->OutStreamer->EmitCFIStartProc(/*IsSimple=*/false);
146 
147   // Indicate personality routine, if any.
148   if (!shouldEmitPersonality)
149     return;
150 
151   auto *F = MBB->getParent()->getFunction();
152   auto *P = dyn_cast<Function>(F->getPersonalityFn()->stripPointerCasts());
153   assert(P && "Expected personality function");
154 
155   // If we are forced to emit this personality, make sure to record
156   // it because it might not appear in any landingpad
157   if (forceEmitPersonality)
158     MMI->addPersonality(P);
159 
160   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
161   unsigned PerEncoding = TLOF.getPersonalityEncoding();
162   const MCSymbol *Sym = TLOF.getCFIPersonalitySymbol(P, Asm->TM, MMI);
163   Asm->OutStreamer->EmitCFIPersonality(Sym, PerEncoding);
164 
165   // Provide LSDA information.
166   if (shouldEmitLSDA)
167     Asm->OutStreamer->EmitCFILsda(ESP(Asm), TLOF.getLSDAEncoding());
168 }
169 
170 /// endFunction - Gather and emit post-function exception information.
171 ///
172 void DwarfCFIException::endFunction(const MachineFunction *MF) {
173   if (!shouldEmitPersonality)
174     return;
175 
176   emitExceptionTable();
177 }
178