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 /// Structure describing a contiguous range of call-sites which reside 73 /// in the same procedure fragment. With -fbasic-block-sections, there will 74 /// be one call site range per basic block section. Otherwise, we will have 75 /// one call site range containing all the call sites in the function. 76 struct CallSiteRange { 77 // Symbol marking the beginning of the precedure fragment. 78 MCSymbol *FragmentBeginLabel = nullptr; 79 // Symbol marking the end of the procedure fragment. 80 MCSymbol *FragmentEndLabel = nullptr; 81 // LSDA symbol for this call-site range. 82 MCSymbol *ExceptionLabel = nullptr; 83 // Index of the first call-site entry in the call-site table which 84 // belongs to this range. 85 size_t CallSiteBeginIdx = 0; 86 // Index just after the last call-site entry in the call-site table which 87 // belongs to this range. 88 size_t CallSiteEndIdx = 0; 89 // Whether this is the call-site range containing all the landing pads. 90 bool IsLPRange = false; 91 }; 92 93 /// Compute the actions table and gather the first action index for each 94 /// landing pad site. 95 void computeActionsTable( 96 const SmallVectorImpl<const LandingPadInfo *> &LandingPads, 97 SmallVectorImpl<ActionEntry> &Actions, 98 SmallVectorImpl<unsigned> &FirstActions); 99 100 void computePadMap(const SmallVectorImpl<const LandingPadInfo *> &LandingPads, 101 RangeMapType &PadMap); 102 103 /// Compute the call-site table and the call-site ranges. The entry for an 104 /// invoke has a try-range containing the call, a non-zero landing pad and an 105 /// appropriate action. The entry for an ordinary call has a try-range 106 /// containing the call and zero for the landing pad and the action. Calls 107 /// marked 'nounwind' have no entry and must not be contained in the try-range 108 /// of any entry - they form gaps in the table. Entries must be ordered by 109 /// try-range address. CallSiteRanges vector is only populated for Itanium 110 /// exception handling. 111 virtual void computeCallSiteTable( 112 SmallVectorImpl<CallSiteEntry> &CallSites, 113 SmallVectorImpl<CallSiteRange> &CallSiteRanges, 114 const SmallVectorImpl<const LandingPadInfo *> &LandingPads, 115 const SmallVectorImpl<unsigned> &FirstActions); 116 117 /// Emit landing pads and actions. 118 /// 119 /// The general organization of the table is complex, but the basic concepts 120 /// are easy. First there is a header which describes the location and 121 /// organization of the three components that follow. 122 /// 1. The landing pad site information describes the range of code covered 123 /// by the try. In our case it's an accumulation of the ranges covered 124 /// by the invokes in the try. There is also a reference to the landing 125 /// pad that handles the exception once processed. Finally an index into 126 /// the actions table. 127 /// 2. The action table, in our case, is composed of pairs of type ids 128 /// and next action offset. Starting with the action index from the 129 /// landing pad site, each type Id is checked for a match to the current 130 /// exception. If it matches then the exception and type id are passed 131 /// on to the landing pad. Otherwise the next action is looked up. This 132 /// chain is terminated with a next action of zero. If no type id is 133 /// found the frame is unwound and handling continues. 134 /// 3. Type id table contains references to all the C++ typeinfo for all 135 /// catches in the function. This tables is reversed indexed base 1. 136 /// 137 /// Returns the starting symbol of an exception table. 138 MCSymbol *emitExceptionTable(); 139 140 virtual void emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel); 141 142 // Helpers for identifying what kind of clause an EH typeid or selector 143 // corresponds to. Negative selectors are for filter clauses, the zero 144 // selector is for cleanups, and positive selectors are for catch clauses. isFilterEHSelector(int Selector)145 static bool isFilterEHSelector(int Selector) { return Selector < 0; } isCleanupEHSelector(int Selector)146 static bool isCleanupEHSelector(int Selector) { return Selector == 0; } isCatchEHSelector(int Selector)147 static bool isCatchEHSelector(int Selector) { return Selector > 0; } 148 149 public: 150 EHStreamer(AsmPrinter *A); 151 ~EHStreamer() override; 152 153 // Unused. setSymbolSize(const MCSymbol * Sym,uint64_t Size)154 void setSymbolSize(const MCSymbol *Sym, uint64_t Size) override {} beginInstruction(const MachineInstr * MI)155 void beginInstruction(const MachineInstr *MI) override {} endInstruction()156 void endInstruction() override {} 157 158 /// Return `true' if this is a call to a function marked `nounwind'. Return 159 /// `false' otherwise. 160 static bool callToNoUnwindFunction(const MachineInstr *MI); 161 }; 162 163 } // end namespace llvm 164 165 #endif // LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H 166