github.com/Cleverse/go-ethereum@v0.0.0-20220927095127-45113064e7f2/core/vm/analysis.go (about)

     1  // Copyright 2014 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  package vm
    18  
    19  const (
    20  	set2BitsMask = uint16(0b11)
    21  	set3BitsMask = uint16(0b111)
    22  	set4BitsMask = uint16(0b1111)
    23  	set5BitsMask = uint16(0b1_1111)
    24  	set6BitsMask = uint16(0b11_1111)
    25  	set7BitsMask = uint16(0b111_1111)
    26  )
    27  
    28  // bitvec is a bit vector which maps bytes in a program.
    29  // An unset bit means the byte is an opcode, a set bit means
    30  // it's data (i.e. argument of PUSHxx).
    31  type bitvec []byte
    32  
    33  func (bits bitvec) set1(pos uint64) {
    34  	bits[pos/8] |= 1 << (pos % 8)
    35  }
    36  
    37  func (bits bitvec) setN(flag uint16, pos uint64) {
    38  	a := flag << (pos % 8)
    39  	bits[pos/8] |= byte(a)
    40  	if b := byte(a >> 8); b != 0 {
    41  		bits[pos/8+1] = b
    42  	}
    43  }
    44  
    45  func (bits bitvec) set8(pos uint64) {
    46  	a := byte(0xFF << (pos % 8))
    47  	bits[pos/8] |= a
    48  	bits[pos/8+1] = ^a
    49  }
    50  
    51  func (bits bitvec) set16(pos uint64) {
    52  	a := byte(0xFF << (pos % 8))
    53  	bits[pos/8] |= a
    54  	bits[pos/8+1] = 0xFF
    55  	bits[pos/8+2] = ^a
    56  }
    57  
    58  // codeSegment checks if the position is in a code segment.
    59  func (bits *bitvec) codeSegment(pos uint64) bool {
    60  	return (((*bits)[pos/8] >> (pos % 8)) & 1) == 0
    61  }
    62  
    63  // codeBitmap collects data locations in code.
    64  func codeBitmap(code []byte) bitvec {
    65  	// The bitmap is 4 bytes longer than necessary, in case the code
    66  	// ends with a PUSH32, the algorithm will push zeroes onto the
    67  	// bitvector outside the bounds of the actual code.
    68  	bits := make(bitvec, len(code)/8+1+4)
    69  	return codeBitmapInternal(code, bits)
    70  }
    71  
    72  // codeBitmapInternal is the internal implementation of codeBitmap.
    73  // It exists for the purpose of being able to run benchmark tests
    74  // without dynamic allocations affecting the results.
    75  func codeBitmapInternal(code, bits bitvec) bitvec {
    76  	for pc := uint64(0); pc < uint64(len(code)); {
    77  		op := OpCode(code[pc])
    78  		pc++
    79  		if int8(op) < int8(PUSH1) { // If not PUSH (the int8(op) > int(PUSH32) is always false).
    80  			continue
    81  		}
    82  		numbits := op - PUSH1 + 1
    83  		if numbits >= 8 {
    84  			for ; numbits >= 16; numbits -= 16 {
    85  				bits.set16(pc)
    86  				pc += 16
    87  			}
    88  			for ; numbits >= 8; numbits -= 8 {
    89  				bits.set8(pc)
    90  				pc += 8
    91  			}
    92  		}
    93  		switch numbits {
    94  		case 1:
    95  			bits.set1(pc)
    96  			pc += 1
    97  		case 2:
    98  			bits.setN(set2BitsMask, pc)
    99  			pc += 2
   100  		case 3:
   101  			bits.setN(set3BitsMask, pc)
   102  			pc += 3
   103  		case 4:
   104  			bits.setN(set4BitsMask, pc)
   105  			pc += 4
   106  		case 5:
   107  			bits.setN(set5BitsMask, pc)
   108  			pc += 5
   109  		case 6:
   110  			bits.setN(set6BitsMask, pc)
   111  			pc += 6
   112  		case 7:
   113  			bits.setN(set7BitsMask, pc)
   114  			pc += 7
   115  		}
   116  	}
   117  	return bits
   118  }