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/IR/Function.h"
19#include "llvm/MC/MCAsmInfo.h"
20#include "llvm/MC/MCContext.h"
21#include "llvm/MC/MCStreamer.h"
22#include "llvm/Target/TargetLoweringObjectFile.h"
23#include "llvm/Target/TargetMachine.h"
24#include "llvm/Target/TargetOptions.h"
25using namespace llvm;
26
27DwarfCFIException::DwarfCFIException(AsmPrinter *A) : EHStreamer(A) {}
28
29DwarfCFIException::~DwarfCFIException() = default;
30
31void DwarfCFIException::addPersonality(const GlobalValue *Personality) {
32 if (!llvm::is_contained(Range&: Personalities, Element: Personality))
33 Personalities.push_back(x: Personality);
34}
35
36/// endModule - Emit all exception information that should come after the
37/// content.
38void DwarfCFIException::endModule() {
39 // SjLj uses this pass and it doesn't need this info.
40 if (!Asm->MAI->usesCFIForEH())
41 return;
42
43 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
44
45 unsigned PerEncoding = TLOF.getPersonalityEncoding();
46
47 if ((PerEncoding & 0x80) != dwarf::DW_EH_PE_indirect)
48 return;
49
50 // Emit indirect reference table for all used personality functions
51 for (const GlobalValue *Personality : Personalities) {
52 MCSymbol *Sym = Asm->getSymbol(GV: Personality);
53 TLOF.emitPersonalityValue(Streamer&: *Asm->OutStreamer, TM: Asm->getDataLayout(), Sym,
54 MMI: Asm->MMI);
55 }
56 Personalities.clear();
57}
58
59void DwarfCFIException::beginFunction(const MachineFunction *MF) {
60 shouldEmitPersonality = shouldEmitLSDA = false;
61 const Function &F = MF->getFunction();
62
63 // If any landing pads survive, we need an EH table.
64 bool hasLandingPads = !MF->getLandingPads().empty();
65
66 // See if we need frame move info.
67 bool shouldEmitMoves =
68 Asm->getFunctionCFISectionType(MF: *MF) != AsmPrinter::CFISection::None;
69
70 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
71 unsigned PerEncoding = TLOF.getPersonalityEncoding();
72 const GlobalValue *Per = nullptr;
73 if (F.hasPersonalityFn())
74 Per = dyn_cast<GlobalValue>(Val: F.getPersonalityFn()->stripPointerCasts());
75
76 // Emit a personality function even when there are no landing pads
77 forceEmitPersonality =
78 // ...if a personality function is explicitly specified
79 F.hasPersonalityFn() &&
80 // ... and it's not known to be a noop in the absence of invokes
81 !isNoOpWithoutInvoke(Pers: classifyEHPersonality(Pers: Per)) &&
82 // ... and we're not explicitly asked not to emit it
83 F.needsUnwindTableEntry();
84
85 shouldEmitPersonality =
86 (forceEmitPersonality ||
87 (hasLandingPads && PerEncoding != dwarf::DW_EH_PE_omit)) &&
88 Per;
89
90 unsigned LSDAEncoding = TLOF.getLSDAEncoding();
91 shouldEmitLSDA = shouldEmitPersonality &&
92 LSDAEncoding != dwarf::DW_EH_PE_omit;
93
94 const MCAsmInfo &MAI = *MF->getContext().getAsmInfo();
95 if (MAI.getExceptionHandlingType() != ExceptionHandling::None)
96 shouldEmitCFI =
97 MAI.usesCFIForEH() && (shouldEmitPersonality || shouldEmitMoves);
98 else
99 shouldEmitCFI = Asm->usesCFIWithoutEH() && shouldEmitMoves;
100}
101
102void DwarfCFIException::beginBasicBlockSection(const MachineBasicBlock &MBB) {
103 if (!shouldEmitCFI)
104 return;
105
106 if (!hasEmittedCFISections) {
107 AsmPrinter::CFISection CFISecType = Asm->getModuleCFISectionType();
108 // If we don't say anything it implies `.cfi_sections .eh_frame`, so we
109 // chose not to be verbose in that case. And with `ForceDwarfFrameSection`,
110 // we should always emit .debug_frame.
111 if (CFISecType == AsmPrinter::CFISection::Debug ||
112 Asm->TM.Options.ForceDwarfFrameSection)
113 Asm->OutStreamer->emitCFISections(
114 EH: CFISecType == AsmPrinter::CFISection::EH, Debug: true);
115 hasEmittedCFISections = true;
116 }
117
118 Asm->OutStreamer->emitCFIStartProc(/*IsSimple=*/false);
119
120 // Indicate personality routine, if any.
121 if (!shouldEmitPersonality)
122 return;
123
124 auto &F = MBB.getParent()->getFunction();
125 auto *P = dyn_cast<GlobalValue>(Val: F.getPersonalityFn()->stripPointerCasts());
126 assert(P && "Expected personality function");
127 // Record the personality function.
128 addPersonality(Personality: P);
129
130 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
131 unsigned PerEncoding = TLOF.getPersonalityEncoding();
132 const MCSymbol *Sym = TLOF.getCFIPersonalitySymbol(GV: P, TM: Asm->TM, MMI);
133 Asm->OutStreamer->emitCFIPersonality(Sym, Encoding: PerEncoding);
134
135 // Provide LSDA information.
136 if (shouldEmitLSDA)
137 Asm->OutStreamer->emitCFILsda(Sym: Asm->getMBBExceptionSym(MBB),
138 Encoding: TLOF.getLSDAEncoding());
139}
140
141void DwarfCFIException::endBasicBlockSection(const MachineBasicBlock &MBB) {
142 if (shouldEmitCFI)
143 Asm->OutStreamer->emitCFIEndProc();
144}
145
146/// endFunction - Gather and emit post-function exception information.
147///
148void DwarfCFIException::endFunction(const MachineFunction *MF) {
149 if (!shouldEmitPersonality)
150 return;
151
152 emitExceptionTable();
153}
154