x/net/bpf: proper disassemble "fake" jump conditions

[breml]

What version of Go are you using (go version)?

go version go1.7.4 linux/amd64

What operating system and processor architecture are you using (go env)?

linux, amd64

What did you do?

Disassemble bpf conditional jump instructions: jneq (jne), jlt, jle.

package main

import (
	"log"
	"reflect"
	"golang.org/x/net/bpf"
)

var allInstructions = []bpf.Instruction{
	bpf.JumpIf{Cond: bpf.JumpNotEqual, Val: 42, SkipTrue: 8},
	bpf.JumpIf{Cond: bpf.JumpLessThan, Val: 42, SkipTrue: 7},
	bpf.JumpIf{Cond: bpf.JumpLessOrEqual, Val: 42, SkipTrue: 6},
}

func main() {
	for _, instr := range allInstructions {
		if jumpIfInstr, ok := instr.(bpf.JumpIf); ok {
			gotAsm, err := jumpIfInstr.Assemble()
			if err != nil {
				log.Fatalf("assembly of '%#v' failed: %s", jumpIfInstr, err)
			}
			got := gotAsm.Disassemble()
			if !reflect.DeepEqual(jumpIfInstr, got) {
				log.Printf("program mutated by disassembly, expected: %#v, got: %#v", jumpIfInstr, got)
			}
		}
	}

}

What did you expect to see?

bpf.JumpIf with condition bpf.JumpNotEqual, bpf.JumpLessThan and bpf.JumpLessOrEqual should disassemble to the same types again.

What did you see instead?

Conditions are disassebled to bpf.JumpEqual, bpf.JumpGreaterOrEqual and bpf.JumpGreaterThan.

Similar issue as: #18469

With both issues (this one and #18469) resolved, the test in https://github.com/golang/net/blob/master/bpf/instructions_test.go#L145-L184 could be simplified without the special handling for "fake" jump conditions.

[gopherbot]

CL https://golang.org/cl/34772 mentions this issue.

[gopherbot]

CL https://golang.org/cl/34951 mentions this issue.