1 //===- EHStreamer.h - Exception Handling Directive Streamer -----*- C++ -*-===// 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 exception info into assembly files. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #ifndef LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H 14 #define LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H 15 16 #include "llvm/ADT/DenseMap.h" 17 #include "llvm/CodeGen/AsmPrinterHandler.h" 18 #include "llvm/Support/Compiler.h" 19 20 namespace llvm { 21 22 class AsmPrinter; 23 struct LandingPadInfo; 24 class MachineInstr; 25 class MachineModuleInfo; 26 class MCSymbol; 27 template <typename T> class SmallVectorImpl; 28 29 /// Emits exception handling directives. 30 class LLVM_LIBRARY_VISIBILITY EHStreamer : public AsmPrinterHandler { 31 protected: 32 /// Target of directive emission. 33 AsmPrinter *Asm; 34 35 /// Collected machine module information. 36 MachineModuleInfo *MMI; 37 38 /// How many leading type ids two landing pads have in common. 39 static unsigned sharedTypeIDs(const LandingPadInfo *L, 40 const LandingPadInfo *R); 41 42 /// Structure holding a try-range and the associated landing pad. 43 struct PadRange { 44 // The index of the landing pad. 45 unsigned PadIndex; 46 47 // The index of the begin and end labels in the landing pad's label lists. 48 unsigned RangeIndex; 49 }; 50 51 using RangeMapType = DenseMap<MCSymbol *, PadRange>; 52 53 /// Structure describing an entry in the actions table. 54 struct ActionEntry { 55 int ValueForTypeID; // The value to write - may not be equal to the type id. 56 int NextAction; 57 unsigned Previous; 58 }; 59 60 /// Structure describing an entry in the call-site table. 61 struct CallSiteEntry { 62 // The 'try-range' is BeginLabel .. EndLabel. 63 MCSymbol *BeginLabel; // Null indicates the start of the function. 64 MCSymbol *EndLabel; // Null indicates the end of the function. 65 66 // LPad contains the landing pad start labels. 67 const LandingPadInfo *LPad; // Null indicates that there is no landing pad. 68 69 unsigned Action; 70 }; 71 72 /// Compute the actions table and gather the first action index for each 73 /// landing pad site. 74 void computeActionsTable(const SmallVectorImpl<const LandingPadInfo *> &LandingPads, 75 SmallVectorImpl<ActionEntry> &Actions, 76 SmallVectorImpl<unsigned> &FirstActions); 77 78 void computePadMap(const SmallVectorImpl<const LandingPadInfo *> &LandingPads, 79 RangeMapType &PadMap); 80 81 /// Compute the call-site table. The entry for an invoke has a try-range 82 /// containing the call, a non-zero landing pad and an appropriate action. 83 /// The entry for an ordinary call has a try-range containing the call and 84 /// zero for the landing pad and the action. Calls marked 'nounwind' have 85 /// no entry and must not be contained in the try-range of any entry - they 86 /// form gaps in the table. Entries must be ordered by try-range address. 87 virtual void computeCallSiteTable( 88 SmallVectorImpl<CallSiteEntry> &CallSites, 89 const SmallVectorImpl<const LandingPadInfo *> &LandingPads, 90 const SmallVectorImpl<unsigned> &FirstActions); 91 92 /// Emit landing pads and actions. 93 /// 94 /// The general organization of the table is complex, but the basic concepts 95 /// are easy. First there is a header which describes the location and 96 /// organization of the three components that follow. 97 /// 1. The landing pad site information describes the range of code covered 98 /// by the try. In our case it's an accumulation of the ranges covered 99 /// by the invokes in the try. There is also a reference to the landing 100 /// pad that handles the exception once processed. Finally an index into 101 /// the actions table. 102 /// 2. The action table, in our case, is composed of pairs of type ids 103 /// and next action offset. Starting with the action index from the 104 /// landing pad site, each type Id is checked for a match to the current 105 /// exception. If it matches then the exception and type id are passed 106 /// on to the landing pad. Otherwise the next action is looked up. This 107 /// chain is terminated with a next action of zero. If no type id is 108 /// found the frame is unwound and handling continues. 109 /// 3. Type id table contains references to all the C++ typeinfo for all 110 /// catches in the function. This tables is reversed indexed base 1. 111 /// 112 /// Returns the starting symbol of an exception table. 113 MCSymbol *emitExceptionTable(); 114 115 virtual void emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel); 116 117 // Helpers for identifying what kind of clause an EH typeid or selector 118 // corresponds to. Negative selectors are for filter clauses, the zero 119 // selector is for cleanups, and positive selectors are for catch clauses. 120 static bool isFilterEHSelector(int Selector) { return Selector < 0; } 121 static bool isCleanupEHSelector(int Selector) { return Selector == 0; } 122 static bool isCatchEHSelector(int Selector) { return Selector > 0; } 123 124 public: 125 EHStreamer(AsmPrinter *A); 126 ~EHStreamer() override; 127 128 // Unused. 129 void setSymbolSize(const MCSymbol *Sym, uint64_t Size) override {} 130 void beginInstruction(const MachineInstr *MI) override {} 131 void endInstruction() override {} 132 133 /// Return `true' if this is a call to a function marked `nounwind'. Return 134 /// `false' otherwise. 135 static bool callToNoUnwindFunction(const MachineInstr *MI); 136 }; 137 138 } // end namespace llvm 139 140 #endif // LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H 141