1 //===-- CodeGen/AsmPrinter/DwarfException.cpp - Dwarf Exception Impl ------===//
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 support for writing DWARF exception info into asm files.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "DwarfException.h"
14 #include "llvm/BinaryFormat/Dwarf.h"
15 #include "llvm/CodeGen/AsmPrinter.h"
16 #include "llvm/CodeGen/MachineFunction.h"
17 #include "llvm/CodeGen/MachineModuleInfo.h"
18 #include "llvm/MC/MCAsmInfo.h"
19 #include "llvm/MC/MCContext.h"
20 #include "llvm/MC/MCStreamer.h"
21 #include "llvm/Target/TargetLoweringObjectFile.h"
22 #include "llvm/Target/TargetMachine.h"
23 #include "llvm/Target/TargetOptions.h"
24 using namespace llvm;
25 
26 DwarfCFIExceptionBase::DwarfCFIExceptionBase(AsmPrinter *A) : EHStreamer(A) {}
27 
28 void DwarfCFIExceptionBase::markFunctionEnd() {
29   endFragment();
30 
31   // Map all labels and get rid of any dead landing pads.
32   if (!Asm->MF->getLandingPads().empty()) {
33     MachineFunction *NonConstMF = const_cast<MachineFunction*>(Asm->MF);
34     NonConstMF->tidyLandingPads();
35   }
36 }
37 
38 void DwarfCFIExceptionBase::endFragment() {
39   if (shouldEmitCFI && !Asm->MF->hasBBSections())
40     Asm->OutStreamer->emitCFIEndProc();
41 }
42 
43 DwarfCFIException::DwarfCFIException(AsmPrinter *A)
44     : DwarfCFIExceptionBase(A) {}
45 
46 DwarfCFIException::~DwarfCFIException() = default;
47 
48 /// endModule - Emit all exception information that should come after the
49 /// content.
50 void DwarfCFIException::endModule() {
51   // SjLj uses this pass and it doesn't need this info.
52   if (!Asm->MAI->usesCFIForEH())
53     return;
54 
55   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
56 
57   unsigned PerEncoding = TLOF.getPersonalityEncoding();
58 
59   if ((PerEncoding & 0x80) != dwarf::DW_EH_PE_indirect)
60     return;
61 
62   // Emit references to all used personality functions
63   for (const Function *Personality : MMI->getPersonalities()) {
64     if (!Personality)
65       continue;
66     MCSymbol *Sym = Asm->getSymbol(Personality);
67     TLOF.emitPersonalityValue(*Asm->OutStreamer, Asm->getDataLayout(), Sym);
68   }
69 }
70 
71 static MCSymbol *getExceptionSym(AsmPrinter *Asm,
72                                  const MachineBasicBlock *MBB) {
73   return Asm->getMBBExceptionSym(*MBB);
74 }
75 
76 void DwarfCFIException::beginFunction(const MachineFunction *MF) {
77   shouldEmitPersonality = shouldEmitLSDA = false;
78   const Function &F = MF->getFunction();
79 
80   // If any landing pads survive, we need an EH table.
81   bool hasLandingPads = !MF->getLandingPads().empty();
82 
83   // See if we need frame move info.
84   bool shouldEmitMoves =
85       Asm->getFunctionCFISectionType(*MF) != AsmPrinter::CFISection::None;
86 
87   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
88   unsigned PerEncoding = TLOF.getPersonalityEncoding();
89   const Function *Per = nullptr;
90   if (F.hasPersonalityFn())
91     Per = dyn_cast<Function>(F.getPersonalityFn()->stripPointerCasts());
92 
93   // Emit a personality function even when there are no landing pads
94   forceEmitPersonality =
95       // ...if a personality function is explicitly specified
96       F.hasPersonalityFn() &&
97       // ... and it's not known to be a noop in the absence of invokes
98       !isNoOpWithoutInvoke(classifyEHPersonality(Per)) &&
99       // ... and we're not explicitly asked not to emit it
100       F.needsUnwindTableEntry();
101 
102   shouldEmitPersonality =
103       (forceEmitPersonality ||
104        (hasLandingPads && PerEncoding != dwarf::DW_EH_PE_omit)) &&
105       Per;
106 
107   unsigned LSDAEncoding = TLOF.getLSDAEncoding();
108   shouldEmitLSDA = shouldEmitPersonality &&
109     LSDAEncoding != dwarf::DW_EH_PE_omit;
110 
111   const MCAsmInfo &MAI = *MF->getMMI().getContext().getAsmInfo();
112   if (MAI.getExceptionHandlingType() != ExceptionHandling::None)
113     shouldEmitCFI =
114         MAI.usesCFIForEH() && (shouldEmitPersonality || shouldEmitMoves);
115   else
116     shouldEmitCFI = Asm->needsCFIForDebug() && shouldEmitMoves;
117 
118   beginFragment(&*MF->begin(), getExceptionSym);
119 }
120 
121 void DwarfCFIException::beginFragment(const MachineBasicBlock *MBB,
122                                       ExceptionSymbolProvider ESP) {
123   if (!shouldEmitCFI)
124     return;
125 
126   if (!hasEmittedCFISections) {
127     AsmPrinter::CFISection CFISecType = Asm->getModuleCFISectionType();
128     // If we don't say anything it implies `.cfi_sections .eh_frame`, so we
129     // chose not to be verbose in that case. And with `ForceDwarfFrameSection`,
130     // we should always emit .debug_frame.
131     if (CFISecType == AsmPrinter::CFISection::Debug ||
132         Asm->TM.Options.ForceDwarfFrameSection)
133       Asm->OutStreamer->emitCFISections(
134           CFISecType == AsmPrinter::CFISection::EH, true);
135     hasEmittedCFISections = true;
136   }
137 
138   Asm->OutStreamer->emitCFIStartProc(/*IsSimple=*/false);
139 
140   // Indicate personality routine, if any.
141   if (!shouldEmitPersonality)
142     return;
143 
144   auto &F = MBB->getParent()->getFunction();
145   auto *P = dyn_cast<Function>(F.getPersonalityFn()->stripPointerCasts());
146   assert(P && "Expected personality function");
147 
148   // If we are forced to emit this personality, make sure to record
149   // it because it might not appear in any landingpad
150   if (forceEmitPersonality)
151     MMI->addPersonality(P);
152 
153   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
154   unsigned PerEncoding = TLOF.getPersonalityEncoding();
155   const MCSymbol *Sym = TLOF.getCFIPersonalitySymbol(P, Asm->TM, MMI);
156   Asm->OutStreamer->emitCFIPersonality(Sym, PerEncoding);
157 
158   // Provide LSDA information.
159   if (shouldEmitLSDA)
160     Asm->OutStreamer->emitCFILsda(ESP(Asm, MBB), TLOF.getLSDAEncoding());
161 }
162 
163 /// endFunction - Gather and emit post-function exception information.
164 ///
165 void DwarfCFIException::endFunction(const MachineFunction *MF) {
166   if (!shouldEmitPersonality)
167     return;
168 
169   emitExceptionTable();
170 }
171 
172 void DwarfCFIException::beginBasicBlock(const MachineBasicBlock &MBB) {
173   beginFragment(&MBB, getExceptionSym);
174 }
175 
176 void DwarfCFIException::endBasicBlock(const MachineBasicBlock &MBB) {
177   if (shouldEmitCFI)
178     Asm->OutStreamer->emitCFIEndProc();
179 }
180