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