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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package bpf
import (
"encoding/binary"
"fmt"
)
func aluOpConstant(ins ALUOpConstant, regA uint32) uint32 {
return aluOpCommon(ins.Op, regA, ins.Val)
}
func aluOpX(ins ALUOpX, regA uint32, regX uint32) (uint32, bool) {
// Guard against division or modulus by zero by terminating
// the program, as the OS BPF VM does
if regX == 0 {
switch ins.Op {
case ALUOpDiv, ALUOpMod:
return 0, false
}
}
return aluOpCommon(ins.Op, regA, regX), true
}
func aluOpCommon(op ALUOp, regA uint32, value uint32) uint32 {
switch op {
case ALUOpAdd:
return regA + value
case ALUOpSub:
return regA - value
case ALUOpMul:
return regA * value
case ALUOpDiv:
// Division by zero not permitted by NewVM and aluOpX checks
return regA / value
case ALUOpOr:
return regA | value
case ALUOpAnd:
return regA & value
case ALUOpShiftLeft:
return regA << value
case ALUOpShiftRight:
return regA >> value
case ALUOpMod:
// Modulus by zero not permitted by NewVM and aluOpX checks
return regA % value
case ALUOpXor:
return regA ^ value
default:
return regA
}
}
func jumpIf(ins JumpIf, regA uint32) int {
return jumpIfCommon(ins.Cond, ins.SkipTrue, ins.SkipFalse, regA, ins.Val)
}
func jumpIfX(ins JumpIfX, regA uint32, regX uint32) int {
return jumpIfCommon(ins.Cond, ins.SkipTrue, ins.SkipFalse, regA, regX)
}
func jumpIfCommon(cond JumpTest, skipTrue, skipFalse uint8, regA uint32, value uint32) int {
var ok bool
switch cond {
case JumpEqual:
ok = regA == value
case JumpNotEqual:
ok = regA != value
case JumpGreaterThan:
ok = regA > value
case JumpLessThan:
ok = regA < value
case JumpGreaterOrEqual:
ok = regA >= value
case JumpLessOrEqual:
ok = regA <= value
case JumpBitsSet:
ok = (regA & value) != 0
case JumpBitsNotSet:
ok = (regA & value) == 0
}
if ok {
return int(skipTrue)
}
return int(skipFalse)
}
func loadAbsolute(ins LoadAbsolute, in []byte) (uint32, bool) {
offset := int(ins.Off)
size := ins.Size
return loadCommon(in, offset, size)
}
func loadConstant(ins LoadConstant, regA uint32, regX uint32) (uint32, uint32) {
switch ins.Dst {
case RegA:
regA = ins.Val
case RegX:
regX = ins.Val
}
return regA, regX
}
func loadExtension(ins LoadExtension, in []byte) uint32 {
switch ins.Num {
case ExtLen:
return uint32(len(in))
default:
panic(fmt.Sprintf("unimplemented extension: %d", ins.Num))
}
}
func loadIndirect(ins LoadIndirect, in []byte, regX uint32) (uint32, bool) {
offset := int(ins.Off) + int(regX)
size := ins.Size
return loadCommon(in, offset, size)
}
func loadMemShift(ins LoadMemShift, in []byte) (uint32, bool) {
offset := int(ins.Off)
// Size of LoadMemShift is always 1 byte
if !inBounds(len(in), offset, 1) {
return 0, false
}
// Mask off high 4 bits and multiply low 4 bits by 4
return uint32(in[offset]&0x0f) * 4, true
}
func inBounds(inLen int, offset int, size int) bool {
return offset+size <= inLen
}
func loadCommon(in []byte, offset int, size int) (uint32, bool) {
if !inBounds(len(in), offset, size) {
return 0, false
}
switch size {
case 1:
return uint32(in[offset]), true
case 2:
return uint32(binary.BigEndian.Uint16(in[offset : offset+size])), true
case 4:
return uint32(binary.BigEndian.Uint32(in[offset : offset+size])), true
default:
panic(fmt.Sprintf("invalid load size: %d", size))
}
}
func loadScratch(ins LoadScratch, regScratch [16]uint32, regA uint32, regX uint32) (uint32, uint32) {
switch ins.Dst {
case RegA:
regA = regScratch[ins.N]
case RegX:
regX = regScratch[ins.N]
}
return regA, regX
}
func storeScratch(ins StoreScratch, regScratch [16]uint32, regA uint32, regX uint32) [16]uint32 {
switch ins.Src {
case RegA:
regScratch[ins.N] = regA
case RegX:
regScratch[ins.N] = regX
}
return regScratch
}
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