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/ADT/Twine.h"
15 #include "llvm/BinaryFormat/Dwarf.h"
16 #include "llvm/CodeGen/AsmPrinter.h"
17 #include "llvm/CodeGen/MachineFunction.h"
18 #include "llvm/CodeGen/MachineModuleInfo.h"
19 #include "llvm/IR/DataLayout.h"
20 #include "llvm/IR/Mangler.h"
21 #include "llvm/IR/Module.h"
22 #include "llvm/MC/MCAsmInfo.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCExpr.h"
25 #include "llvm/MC/MCSection.h"
26 #include "llvm/MC/MCStreamer.h"
27 #include "llvm/MC/MCSymbol.h"
28 #include "llvm/MC/MachineLocation.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/FormattedStream.h"
31 #include "llvm/Target/TargetLoweringObjectFile.h"
32 #include "llvm/Target/TargetMachine.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 && !Asm->MF->hasBBSections())
51     Asm->OutStreamer->emitCFIEndProc();
52 }
53 
54 DwarfCFIException::DwarfCFIException(AsmPrinter *A)
55     : DwarfCFIExceptionBase(A), shouldEmitPersonality(false),
56       forceEmitPersonality(false), shouldEmitLSDA(false) {}
57 
58 DwarfCFIException::~DwarfCFIException() {}
59 
60 /// endModule - Emit all exception information that should come after the
61 /// content.
62 void DwarfCFIException::endModule() {
63   // SjLj uses this pass and it doesn't need this info.
64   if (!Asm->MAI->usesCFIForEH())
65     return;
66 
67   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
68 
69   unsigned PerEncoding = TLOF.getPersonalityEncoding();
70 
71   if ((PerEncoding & 0x80) != dwarf::DW_EH_PE_indirect)
72     return;
73 
74   // Emit references to all used personality functions
75   for (const Function *Personality : MMI->getPersonalities()) {
76     if (!Personality)
77       continue;
78     MCSymbol *Sym = Asm->getSymbol(Personality);
79     TLOF.emitPersonalityValue(*Asm->OutStreamer, Asm->getDataLayout(), Sym);
80   }
81 }
82 
83 static MCSymbol *getExceptionSym(AsmPrinter *Asm,
84                                  const MachineBasicBlock *MBB) {
85   return Asm->getMBBExceptionSym(*MBB);
86 }
87 
88 void DwarfCFIException::beginFunction(const MachineFunction *MF) {
89   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   bool shouldEmitMoves =
97       Asm->getFunctionCFISectionType(*MF) != AsmPrinter::CFISection::None;
98 
99   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
100   unsigned PerEncoding = TLOF.getPersonalityEncoding();
101   const Function *Per = nullptr;
102   if (F.hasPersonalityFn())
103     Per = dyn_cast<Function>(F.getPersonalityFn()->stripPointerCasts());
104 
105   // Emit a personality function even when there are no landing pads
106   forceEmitPersonality =
107       // ...if a personality function is explicitly specified
108       F.hasPersonalityFn() &&
109       // ... and it's not known to be a noop in the absence of invokes
110       !isNoOpWithoutInvoke(classifyEHPersonality(Per)) &&
111       // ... and we're not explicitly asked not to emit it
112       F.needsUnwindTableEntry();
113 
114   shouldEmitPersonality =
115       (forceEmitPersonality ||
116        (hasLandingPads && PerEncoding != dwarf::DW_EH_PE_omit)) &&
117       Per;
118 
119   unsigned LSDAEncoding = TLOF.getLSDAEncoding();
120   shouldEmitLSDA = shouldEmitPersonality &&
121     LSDAEncoding != dwarf::DW_EH_PE_omit;
122 
123   shouldEmitCFI = MF->getMMI().getContext().getAsmInfo()->usesCFIForEH() &&
124                   (shouldEmitPersonality || shouldEmitMoves);
125   beginFragment(&*MF->begin(), getExceptionSym);
126 }
127 
128 void DwarfCFIException::beginFragment(const MachineBasicBlock *MBB,
129                                       ExceptionSymbolProvider ESP) {
130   if (!shouldEmitCFI)
131     return;
132 
133   if (!hasEmittedCFISections) {
134     AsmPrinter::CFISection CFISecType = Asm->getModuleCFISectionType();
135     // If we don't say anything it implies `.cfi_sections .eh_frame`, so we
136     // chose not to be verbose in that case. And with `ForceDwarfFrameSection`,
137     // we should always emit .debug_frame.
138     if (CFISecType == AsmPrinter::CFISection::Debug ||
139         Asm->TM.Options.ForceDwarfFrameSection)
140       Asm->OutStreamer->emitCFISections(
141           CFISecType == AsmPrinter::CFISection::EH, 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, MBB), 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 
179 void DwarfCFIException::beginBasicBlock(const MachineBasicBlock &MBB) {
180   beginFragment(&MBB, getExceptionSym);
181 }
182 
183 void DwarfCFIException::endBasicBlock(const MachineBasicBlock &MBB) {
184   if (shouldEmitCFI)
185     Asm->OutStreamer->emitCFIEndProc();
186 }
187