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       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                                  const MachineBasicBlock *MBB) {
86   return Asm->getMBBExceptionSym(*MBB);
87 }
88 
89 void DwarfCFIException::beginFunction(const MachineFunction *MF) {
90   shouldEmitMoves = shouldEmitPersonality = shouldEmitLSDA = false;
91   const Function &F = MF->getFunction();
92 
93   // If any landing pads survive, we need an EH table.
94   bool hasLandingPads = !MF->getLandingPads().empty();
95 
96   // See if we need frame move info.
97   AsmPrinter::CFIMoveType MoveType = Asm->needsCFIMoves();
98 
99   shouldEmitMoves = MoveType != AsmPrinter::CFI_M_None;
100 
101   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
102   unsigned PerEncoding = TLOF.getPersonalityEncoding();
103   const Function *Per = nullptr;
104   if (F.hasPersonalityFn())
105     Per = dyn_cast<Function>(F.getPersonalityFn()->stripPointerCasts());
106 
107   // Emit a personality function even when there are no landing pads
108   forceEmitPersonality =
109       // ...if a personality function is explicitly specified
110       F.hasPersonalityFn() &&
111       // ... and it's not known to be a noop in the absence of invokes
112       !isNoOpWithoutInvoke(classifyEHPersonality(Per)) &&
113       // ... and we're not explicitly asked not to emit it
114       F.needsUnwindTableEntry();
115 
116   shouldEmitPersonality =
117       (forceEmitPersonality ||
118        (hasLandingPads && PerEncoding != dwarf::DW_EH_PE_omit)) &&
119       Per;
120 
121   unsigned LSDAEncoding = TLOF.getLSDAEncoding();
122   shouldEmitLSDA = shouldEmitPersonality &&
123     LSDAEncoding != dwarf::DW_EH_PE_omit;
124 
125   shouldEmitCFI = MF->getMMI().getContext().getAsmInfo()->usesCFIForEH() &&
126                   (shouldEmitPersonality || shouldEmitMoves);
127   beginFragment(&*MF->begin(), getExceptionSym);
128 }
129 
130 void DwarfCFIException::beginFragment(const MachineBasicBlock *MBB,
131                                       ExceptionSymbolProvider ESP) {
132   if (!shouldEmitCFI)
133     return;
134 
135   if (!hasEmittedCFISections) {
136     if (Asm->needsOnlyDebugCFIMoves())
137       Asm->OutStreamer->emitCFISections(false, true);
138     else if (Asm->TM.Options.ForceDwarfFrameSection)
139       Asm->OutStreamer->emitCFISections(true, true);
140     hasEmittedCFISections = true;
141   }
142 
143   Asm->OutStreamer->emitCFIStartProc(/*IsSimple=*/false);
144 
145   // Indicate personality routine, if any.
146   if (!shouldEmitPersonality)
147     return;
148 
149   auto &F = MBB->getParent()->getFunction();
150   auto *P = dyn_cast<Function>(F.getPersonalityFn()->stripPointerCasts());
151   assert(P && "Expected personality function");
152 
153   // If we are forced to emit this personality, make sure to record
154   // it because it might not appear in any landingpad
155   if (forceEmitPersonality)
156     MMI->addPersonality(P);
157 
158   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
159   unsigned PerEncoding = TLOF.getPersonalityEncoding();
160   const MCSymbol *Sym = TLOF.getCFIPersonalitySymbol(P, Asm->TM, MMI);
161   Asm->OutStreamer->emitCFIPersonality(Sym, PerEncoding);
162 
163   // Provide LSDA information.
164   if (shouldEmitLSDA)
165     Asm->OutStreamer->emitCFILsda(ESP(Asm, MBB), TLOF.getLSDAEncoding());
166 }
167 
168 /// endFunction - Gather and emit post-function exception information.
169 ///
170 void DwarfCFIException::endFunction(const MachineFunction *MF) {
171   if (!shouldEmitPersonality)
172     return;
173 
174   emitExceptionTable();
175 }
176 
177 void DwarfCFIException::beginBasicBlock(const MachineBasicBlock &MBB) {
178   beginFragment(&MBB, getExceptionSym);
179 }
180 
181 void DwarfCFIException::endBasicBlock(const MachineBasicBlock &MBB) {
182   if (shouldEmitCFI)
183     Asm->OutStreamer->emitCFIEndProc();
184 }
185