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 DwarfCFIException::DwarfCFIException(AsmPrinter *A) : EHStreamer(A) {}
27 
28 DwarfCFIException::~DwarfCFIException() = default;
29 
30 void DwarfCFIException::addPersonality(const GlobalValue *Personality) {
31   if (!llvm::is_contained(Personalities, Personality))
32     Personalities.push_back(Personality);
33 }
34 
35 /// endModule - Emit all exception information that should come after the
36 /// content.
37 void DwarfCFIException::endModule() {
38   // SjLj uses this pass and it doesn't need this info.
39   if (!Asm->MAI->usesCFIForEH())
40     return;
41 
42   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
43 
44   unsigned PerEncoding = TLOF.getPersonalityEncoding();
45 
46   if ((PerEncoding & 0x80) != dwarf::DW_EH_PE_indirect)
47     return;
48 
49   // Emit indirect reference table for all used personality functions
50   for (const GlobalValue *Personality : Personalities) {
51     MCSymbol *Sym = Asm->getSymbol(Personality);
52     TLOF.emitPersonalityValue(*Asm->OutStreamer, Asm->getDataLayout(), Sym);
53   }
54   Personalities.clear();
55 }
56 
57 void DwarfCFIException::beginFunction(const MachineFunction *MF) {
58   shouldEmitPersonality = shouldEmitLSDA = false;
59   const Function &F = MF->getFunction();
60 
61   // If any landing pads survive, we need an EH table.
62   bool hasLandingPads = !MF->getLandingPads().empty();
63 
64   // See if we need frame move info.
65   bool shouldEmitMoves =
66       Asm->getFunctionCFISectionType(*MF) != AsmPrinter::CFISection::None;
67 
68   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
69   unsigned PerEncoding = TLOF.getPersonalityEncoding();
70   const GlobalValue *Per = nullptr;
71   if (F.hasPersonalityFn())
72     Per = dyn_cast<GlobalValue>(F.getPersonalityFn()->stripPointerCasts());
73 
74   // Emit a personality function even when there are no landing pads
75   forceEmitPersonality =
76       // ...if a personality function is explicitly specified
77       F.hasPersonalityFn() &&
78       // ... and it's not known to be a noop in the absence of invokes
79       !isNoOpWithoutInvoke(classifyEHPersonality(Per)) &&
80       // ... and we're not explicitly asked not to emit it
81       F.needsUnwindTableEntry();
82 
83   shouldEmitPersonality =
84       (forceEmitPersonality ||
85        (hasLandingPads && PerEncoding != dwarf::DW_EH_PE_omit)) &&
86       Per;
87 
88   unsigned LSDAEncoding = TLOF.getLSDAEncoding();
89   shouldEmitLSDA = shouldEmitPersonality &&
90     LSDAEncoding != dwarf::DW_EH_PE_omit;
91 
92   const MCAsmInfo &MAI = *MF->getMMI().getContext().getAsmInfo();
93   if (MAI.getExceptionHandlingType() != ExceptionHandling::None)
94     shouldEmitCFI =
95         MAI.usesCFIForEH() && (shouldEmitPersonality || shouldEmitMoves);
96   else
97     shouldEmitCFI = Asm->usesCFIWithoutEH() && shouldEmitMoves;
98 }
99 
100 void DwarfCFIException::beginBasicBlockSection(const MachineBasicBlock &MBB) {
101   if (!shouldEmitCFI)
102     return;
103 
104   if (!hasEmittedCFISections) {
105     AsmPrinter::CFISection CFISecType = Asm->getModuleCFISectionType();
106     // If we don't say anything it implies `.cfi_sections .eh_frame`, so we
107     // chose not to be verbose in that case. And with `ForceDwarfFrameSection`,
108     // we should always emit .debug_frame.
109     if (CFISecType == AsmPrinter::CFISection::Debug ||
110         Asm->TM.Options.ForceDwarfFrameSection)
111       Asm->OutStreamer->emitCFISections(
112           CFISecType == AsmPrinter::CFISection::EH, true);
113     hasEmittedCFISections = true;
114   }
115 
116   Asm->OutStreamer->emitCFIStartProc(/*IsSimple=*/false);
117 
118   // Indicate personality routine, if any.
119   if (!shouldEmitPersonality)
120     return;
121 
122   auto &F = MBB.getParent()->getFunction();
123   auto *P = dyn_cast<GlobalValue>(F.getPersonalityFn()->stripPointerCasts());
124   assert(P && "Expected personality function");
125   // Record the personality function.
126   addPersonality(P);
127 
128   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
129   unsigned PerEncoding = TLOF.getPersonalityEncoding();
130   const MCSymbol *Sym = TLOF.getCFIPersonalitySymbol(P, Asm->TM, MMI);
131   Asm->OutStreamer->emitCFIPersonality(Sym, PerEncoding);
132 
133   // Provide LSDA information.
134   if (shouldEmitLSDA)
135     Asm->OutStreamer->emitCFILsda(Asm->getMBBExceptionSym(MBB),
136                                   TLOF.getLSDAEncoding());
137 }
138 
139 void DwarfCFIException::endBasicBlockSection(const MachineBasicBlock &MBB) {
140   if (shouldEmitCFI)
141     Asm->OutStreamer->emitCFIEndProc();
142 }
143 
144 /// endFunction - Gather and emit post-function exception information.
145 ///
146 void DwarfCFIException::endFunction(const MachineFunction *MF) {
147   if (!shouldEmitPersonality)
148     return;
149 
150   emitExceptionTable();
151 }
152