_ Git - BearSSL/blob - T0/Opcode.cs

   1 /*
   2  * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 using System;
  26 using System.Collections.Generic;
  27
  28 abstract class Opcode {
  29
  30         internal Opcode()
  31         {
  32         }
  33
  34         /*
  35          * Execute this opcode.
  36          */
  37         internal abstract void Run(CPU cpu);
  38
  39         /*
  40          * Resolve the target (word reference) for this opcode.
  41          */
  42         internal virtual void ResolveTarget(Word target)
  43         {
  44                 throw new Exception("Not a call opcode");
  45         }
  46
  47         /*
  48          * Resolve the jump offset for this opcode. Displacement is
  49          * relative to the address of the opcode that immediately follows
  50          * the jump code; thus, 0 implies no jump at all.
  51          */
  52         internal virtual void ResolveJump(int disp)
  53         {
  54                 throw new Exception("Not a jump opcode");
  55         }
  56
  57         /*
  58          * Get the Word that this opcode references; this can happen
  59          * only with "call" and "const" opcodes. For all other opcodes,
  60          * this method returns null.
  61          */
  62         internal virtual Word GetReference(T0Comp ctx)
  63         {
  64                 return null;
  65         }
  66
  67         /*
  68          * Get the data block that this opcode references; this can happen
  69          * only with "const" opcodes. For all other opcodes, this method
  70          * returns null.
  71          */
  72         internal virtual ConstData GetDataBlock(T0Comp ctx)
  73         {
  74                 return null;
  75         }
  76
  77         /*
  78          * Test whether this opcode may "fall through", i.e. execution
  79          * may at least potentially proceed to the next opcode.
  80          */
  81         internal virtual bool MayFallThrough {
  82                 get {
  83                         return true;
  84                 }
  85         }
  86
  87         /*
  88          * Get jump displacement. For non-jump opcodes, this returns 0.
  89          */
  90         internal virtual int JumpDisp {
  91                 get {
  92                         return 0;
  93                 }
  94         }
  95
  96         /*
  97          * Get stack effect for this opcode (number of elements added to
  98          * the stack, could be negative). For OpcodeCall, this returns
  99          * 0.
 100          */
 101         internal virtual int StackAction {
 102                 get {
 103                         return 0;
 104                 }
 105         }
 106
 107         internal abstract CodeElement ToCodeElement();
 108
 109         /*
 110          * This method is called for the CodeElement corresponding to
 111          * this opcode, at gcode[off]; it is used to compute actual
 112          * byte jump offsets when converting code to C.
 113          */
 114         internal virtual void FixUp(CodeElement[] gcode, int off)
 115         {
 116         }
 117 }