utils/TableGen/X86ModRMFilters.h

   1 //===- X86ModRMFilters.h - Disassembler ModR/M filterss ---------*- 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 is part of the X86 Disassembler Emitter.
  10 // It contains ModR/M filters that determine which values of the ModR/M byte
  11 //  are valid for a partiuclar instruction.
  12 // Documentation for the disassembler emitter in general can be found in
  13 //  X86DisassemblerEmitter.h.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #ifndef LLVM_UTILS_TABLEGEN_X86MODRMFILTERS_H
  18 #define LLVM_UTILS_TABLEGEN_X86MODRMFILTERS_H
  19
  20 #include "llvm/Support/DataTypes.h"
  21
  22 namespace llvm {
  23
  24 namespace X86Disassembler {
  25
  26 /// ModRMFilter - Abstract base class for clases that recognize patterns in
  27 ///   ModR/M bytes.
  28 class ModRMFilter {
  29   virtual void anchor();
  30 public:
  31   /// Destructor    - Override as necessary.
  32   virtual ~ModRMFilter() { }
  33
  34   /// isDumb        - Indicates whether this filter returns the same value for
  35   ///                 any value of the ModR/M byte.
  36   ///
  37   /// @result       - True if the filter returns the same value for any ModR/M
  38   ///                 byte; false if not.
  39   virtual bool isDumb() const { return false; }
  40
  41   /// accepts       - Indicates whether the filter accepts a particular ModR/M
  42   ///                 byte value.
  43   ///
  44   /// @result       - True if the filter accepts the ModR/M byte; false if not.
  45   virtual bool accepts(uint8_t modRM) const = 0;
  46 };
  47
  48 /// DumbFilter - Accepts any ModR/M byte.  Used for instructions that do not
  49 ///   require a ModR/M byte or instructions where the entire ModR/M byte is used
  50 ///   for operands.
  51 class DumbFilter : public ModRMFilter {
  52   void anchor() override;
  53 public:
  54   bool isDumb() const override {
  55     return true;
  56   }
  57
  58   bool accepts(uint8_t modRM) const override {
  59     return true;
  60   }
  61 };
  62
  63 /// ModFilter - Filters based on the mod bits [bits 7-6] of the ModR/M byte.
  64 ///   Some instructions are classified based on whether they are 11 or anything
  65 ///   else.  This filter performs that classification.
  66 class ModFilter : public ModRMFilter {
  67   void anchor() override;
  68   bool R;
  69 public:
  70   /// Constructor
  71   ///
  72   /// \param r        True if the mod bits of the ModR/M byte must be 11; false
  73   ///                 otherwise.  The name r derives from the fact that the mod
  74   ///                 bits indicate whether the R/M bits [bits 2-0] signify a
  75   ///                 register or a memory operand.
  76   ModFilter(bool r) :
  77     ModRMFilter(),
  78     R(r) {
  79   }
  80
  81   bool accepts(uint8_t modRM) const override {
  82     return (R == ((modRM & 0xc0) == 0xc0));
  83   }
  84 };
  85
  86 /// ExtendedFilter - Extended opcodes are classified based on the value of the
  87 ///   mod field [bits 7-6] and the value of the nnn field [bits 5-3].
  88 class ExtendedFilter : public ModRMFilter {
  89   void anchor() override;
  90   bool R;
  91   uint8_t NNN;
  92 public:
  93   /// Constructor
  94   ///
  95   /// \param r   True if the mod field must be set to 11; false otherwise.
  96   ///            The name is explained at ModFilter.
  97   /// \param nnn The required value of the nnn field.
  98   ExtendedFilter(bool r, uint8_t nnn) :
  99     ModRMFilter(),
 100     R(r),
 101     NNN(nnn) {
 102   }
 103
 104   bool accepts(uint8_t modRM) const override {
 105     return (((R  && ((modRM & 0xc0) == 0xc0)) ||
 106              (!R && ((modRM & 0xc0) != 0xc0))) &&
 107             (((modRM & 0x38) >> 3) == NNN));
 108   }
 109 };
 110
 111 /// ExactFilter - The occasional extended opcode (such as VMCALL or MONITOR)
 112 ///   requires the ModR/M byte to have a specific value.
 113 class ExactFilter : public ModRMFilter {
 114   void anchor() override;
 115   uint8_t ModRM;
 116 public:
 117   /// Constructor
 118   ///
 119   /// \param modRM The required value of the full ModR/M byte.
 120   ExactFilter(uint8_t modRM) :
 121     ModRMFilter(),
 122     ModRM(modRM) {
 123   }
 124
 125   bool accepts(uint8_t modRM) const override {
 126     return (ModRM == modRM);
 127   }
 128 };
 129
 130 } // namespace X86Disassembler
 131
 132 } // namespace llvm
 133
 134 #endif