1 //===-- JumpInstrTables.h: Jump-Instruction Tables --------------*- C++ -*-===// 2 // 3 // This file is distributed under the University of Illinois Open Source 4 // License. See LICENSE.TXT for details. 5 // 6 //===----------------------------------------------------------------------===// 7 /// 8 /// \file 9 /// \brief An implementation of tables consisting of jump instructions 10 /// 11 //===----------------------------------------------------------------------===// 12 13 #ifndef LLVM_CODEGEN_JUMPINSTRTABLES_H 14 #define LLVM_CODEGEN_JUMPINSTRTABLES_H 15 16 #include "llvm/ADT/DenseMap.h" 17 #include "llvm/Pass.h" 18 #include "llvm/Target/TargetOptions.h" 19 20 namespace llvm { 21 class Constant; 22 class Function; 23 class FunctionType; 24 class JumpInstrTableInfo; 25 class Module; 26 27 /// A class to manage a set of jump tables indexed on function type. It looks at 28 /// each function in the module to find all the functions that have the 29 /// jumptable attribute set. For each such function, it creates a new 30 /// jump-instruction-table function and stores the mapping in the ImmutablePass 31 /// JumpInstrTableInfo. 32 /// 33 /// These special functions get lowered in AsmPrinter to assembly of the form: 34 /// \verbatim 35 /// .globl f 36 /// .type f,@function 37 /// .align 8,0x90 38 /// f: 39 /// jmp f_orig@PLT 40 /// \endverbatim 41 /// 42 /// Support for an architecture depends on two functions in TargetInstrInfo: 43 /// getUnconditionalBranch, and getTrap. AsmPrinter uses these to generate the 44 /// appropriate instructions for the jump statement (an unconditional branch) 45 /// and for padding to make the table have a size that is a power of two. This 46 /// padding uses a trap instruction to ensure that calls to this area halt the 47 /// program. The default implementations of these functions call 48 /// llvm_unreachable. 49 class JumpInstrTables : public ModulePass { 50 public: 51 static char ID; 52 53 JumpInstrTables(); 54 JumpInstrTables(JumpTable::JumpTableType JTT); 55 virtual ~JumpInstrTables(); 56 bool runOnModule(Module &M) override; 57 const char *getPassName() const override { return "Jump-Instruction Tables"; } 58 void getAnalysisUsage(AnalysisUsage &AU) const override; 59 60 /// Creates a jump-instruction table function for the Target and adds it to 61 /// the tables. 62 Function *insertEntry(Module &M, Function *Target); 63 64 /// Checks to see if there is already a table for the given FunctionType. 65 bool hasTable(FunctionType *FunTy); 66 67 private: 68 /// The metadata used while a jump table is being built 69 struct TableMeta { 70 /// The number of this table 71 unsigned TableNum; 72 73 /// The current number of jump entries in the table. 74 unsigned Count; 75 }; 76 77 typedef DenseMap<FunctionType *, struct TableMeta> JumpMap; 78 79 /// Maps the function into a subset of function types, depending on the 80 /// jump-instruction table style selected from JumpTableTypes in 81 /// JumpInstrTables.cpp. The choice of mapping determines the number of 82 /// jump-instruction tables generated by this pass. E.g., the simplest mapping 83 /// converts every function type into void f(); so, all functions end up in a 84 /// single table. 85 FunctionType *transformType(FunctionType *FunTy); 86 87 /// The current state of functions and jump entries in the table(s). 88 JumpMap Metadata; 89 90 /// The ImmutablePass that stores information about the generated tables. 91 JumpInstrTableInfo *JITI; 92 93 /// The total number of tables. 94 unsigned TableCount; 95 96 /// The type of tables to build. 97 JumpTable::JumpTableType JTType; 98 }; 99 100 /// Creates a JumpInstrTables pass for the given type of jump table. 101 ModulePass *createJumpInstrTablesPass(JumpTable::JumpTableType JTT); 102 } 103 104 #endif /* LLVM_CODEGEN_JUMPINSTRTABLES_H */ 105
