lib/CodeGen/AsmPrinter/EHStreamer.h

   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