prog: don't require preallocated buffer for exec encoding

If we send exec encoding to the fuzzer, it's not necessary to serialize
exec encoding into existing buffer (currnetly we serialize directly into shmem).
So simplify code by serializing into a new slice.

1 files changed, 7 insertions, 19 deletions

diff --git a/prog/encodingexec.go b/prog/encodingexec.go
index b90f6a6a1..a51aa54d7 100644
--- a/prog/encodingexec.go
+++ b/prog/encodingexec.go
@@ -68,12 +68,11 @@ var ErrExecBufferTooSmall = errors.New("encodingexec: provided buffer is too sma
 // SerializeForExec serializes program p for execution by process pid into the provided buffer.
 // Returns number of bytes written to the buffer.
 // If the provided buffer is too small for the program an error is returned.
-func (p *Prog) SerializeForExec(buffer []byte) (int, error) {
+func (p *Prog) SerializeForExec() ([]byte, error) {
 	p.debugValidate()
 	w := &execContext{
 		target: p.Target,
-		buf:    buffer,
-		eof:    false,
+		buf:    make([]byte, 0, 4<<10),
 		args:   make(map[Arg]argInfo),
 	}
 	for _, c := range p.Calls {
@@ -81,10 +80,10 @@ func (p *Prog) SerializeForExec(buffer []byte) (int, error) {
 		w.serializeCall(c)
 	}
 	w.write(execInstrEOF)
-	if w.eof || w.copyoutSeq > execMaxCommands {
-		return 0, ErrExecBufferTooSmall
+	if len(w.buf) > ExecBufferSize || w.copyoutSeq > execMaxCommands {
+		return nil, ErrExecBufferTooSmall
 	}
-	return len(buffer) - len(w.buf), nil
+	return w.buf, nil
 }
 
 func (w *execContext) serializeCall(c *Call) {
@@ -122,7 +121,6 @@ func (w *execContext) serializeCall(c *Call) {
 type execContext struct {
 	target     *Target
 	buf        []byte
-	eof        bool
 	args       map[Arg]argInfo
 	copyoutSeq uint64
 	// Per-call state cached here to not pass it through all functions.
@@ -252,12 +250,7 @@ func (w *execContext) writeCopyout(c *Call) {
 }
 
 func (w *execContext) write(v uint64) {
-	if len(w.buf) < 8 {
-		w.eof = true
-		return
-	}
-	n := binary.PutVarint(w.buf, int64(v))
-	w.buf = w.buf[n:]
+	w.buf = binary.AppendVarint(w.buf, int64(v))
 }
 
 func (w *execContext) writeArg(arg Arg) {
@@ -303,12 +296,7 @@ func (w *execContext) writeArg(arg Arg) {
 			flags |= execArgDataReadable
 		}
 		w.write(flags)
-		if len(w.buf) < len(data) {
-			w.eof = true
-		} else {
-			n := copy(w.buf, data)
-			w.buf = w.buf[n:]
-		}
+		w.buf = append(w.buf, data...)
 	case *UnionArg:
 		w.writeArg(a.Option)
 	default: