github.com/MetalBlockchain/subnet-evm@v0.4.9/core/vm/analysis.go (about)

     1  // (c) 2019-2020, Ava Labs, Inc.
     2  //
     3  // This file is a derived work, based on the go-ethereum library whose original
     4  // notices appear below.
     5  //
     6  // It is distributed under a license compatible with the licensing terms of the
     7  // original code from which it is derived.
     8  //
     9  // Much love to the original authors for their work.
    10  // **********
    11  // Copyright 2014 The go-ethereum Authors
    12  // This file is part of the go-ethereum library.
    13  //
    14  // The go-ethereum library is free software: you can redistribute it and/or modify
    15  // it under the terms of the GNU Lesser General Public License as published by
    16  // the Free Software Foundation, either version 3 of the License, or
    17  // (at your option) any later version.
    18  //
    19  // The go-ethereum library is distributed in the hope that it will be useful,
    20  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    21  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    22  // GNU Lesser General Public License for more details.
    23  //
    24  // You should have received a copy of the GNU Lesser General Public License
    25  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    26  
    27  package vm
    28  
    29  const (
    30  	set2BitsMask = uint16(0b11)
    31  	set3BitsMask = uint16(0b111)
    32  	set4BitsMask = uint16(0b1111)
    33  	set5BitsMask = uint16(0b1_1111)
    34  	set6BitsMask = uint16(0b11_1111)
    35  	set7BitsMask = uint16(0b111_1111)
    36  )
    37  
    38  // bitvec is a bit vector which maps bytes in a program.
    39  // An unset bit means the byte is an opcode, a set bit means
    40  // it's data (i.e. argument of PUSHxx).
    41  type bitvec []byte
    42  
    43  func (bits bitvec) set1(pos uint64) {
    44  	bits[pos/8] |= 1 << (pos % 8)
    45  }
    46  
    47  func (bits bitvec) setN(flag uint16, pos uint64) {
    48  	a := flag << (pos % 8)
    49  	bits[pos/8] |= byte(a)
    50  	if b := byte(a >> 8); b != 0 {
    51  		bits[pos/8+1] = b
    52  	}
    53  }
    54  
    55  func (bits bitvec) set8(pos uint64) {
    56  	a := byte(0xFF << (pos % 8))
    57  	bits[pos/8] |= a
    58  	bits[pos/8+1] = ^a
    59  }
    60  
    61  func (bits bitvec) set16(pos uint64) {
    62  	a := byte(0xFF << (pos % 8))
    63  	bits[pos/8] |= a
    64  	bits[pos/8+1] = 0xFF
    65  	bits[pos/8+2] = ^a
    66  }
    67  
    68  // codeSegment checks if the position is in a code segment.
    69  func (bits *bitvec) codeSegment(pos uint64) bool {
    70  	return (((*bits)[pos/8] >> (pos % 8)) & 1) == 0
    71  }
    72  
    73  // codeBitmap collects data locations in code.
    74  func codeBitmap(code []byte) bitvec {
    75  	// The bitmap is 4 bytes longer than necessary, in case the code
    76  	// ends with a PUSH32, the algorithm will push zeroes onto the
    77  	// bitvector outside the bounds of the actual code.
    78  	bits := make(bitvec, len(code)/8+1+4)
    79  	return codeBitmapInternal(code, bits)
    80  }
    81  
    82  // codeBitmapInternal is the internal implementation of codeBitmap.
    83  // It exists for the purpose of being able to run benchmark tests
    84  // without dynamic allocations affecting the results.
    85  func codeBitmapInternal(code, bits bitvec) bitvec {
    86  	for pc := uint64(0); pc < uint64(len(code)); {
    87  		op := OpCode(code[pc])
    88  		pc++
    89  		if int8(op) < int8(PUSH1) { // If not PUSH (the int8(op) > int(PUSH32) is always false).
    90  			continue
    91  		}
    92  		numbits := op - PUSH1 + 1
    93  		if numbits >= 8 {
    94  			for ; numbits >= 16; numbits -= 16 {
    95  				bits.set16(pc)
    96  				pc += 16
    97  			}
    98  			for ; numbits >= 8; numbits -= 8 {
    99  				bits.set8(pc)
   100  				pc += 8
   101  			}
   102  		}
   103  		switch numbits {
   104  		case 1:
   105  			bits.set1(pc)
   106  			pc += 1
   107  		case 2:
   108  			bits.setN(set2BitsMask, pc)
   109  			pc += 2
   110  		case 3:
   111  			bits.setN(set3BitsMask, pc)
   112  			pc += 3
   113  		case 4:
   114  			bits.setN(set4BitsMask, pc)
   115  			pc += 4
   116  		case 5:
   117  			bits.setN(set5BitsMask, pc)
   118  			pc += 5
   119  		case 6:
   120  			bits.setN(set6BitsMask, pc)
   121  			pc += 6
   122  		case 7:
   123  			bits.setN(set7BitsMask, pc)
   124  			pc += 7
   125  		}
   126  	}
   127  	return bits
   128  }