From f8f619e676a9c568c10ac690b37f8b414cd0d52b Mon Sep 17 00:00:00 2001
From: Dmitry Vyukov <dvyukov@google.com>
Date: Mon, 15 Apr 2024 14:54:58 +0200
Subject: 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.
---
 prog/encodingexec.go | 26 +++++++-------------------
 1 file changed, 7 insertions(+), 19 deletions(-)

(limited to 'prog/encodingexec.go')

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:
-- 
cgit mrf-deployment