sys/linux: clone args before mutation

Not cloning the argument results in replaceArg() replacing a union
argument with itself, which may lead to inconsistent resource
references.

Add an assertion to detect such cases in the future.

2 files changed, 7 insertions, 0 deletions

diff --git a/prog/clone.go b/prog/clone.go
index 029cf94c4..4523be0eb 100644
--- a/prog/clone.go
+++ b/prog/clone.go
@@ -39,6 +39,10 @@ func cloneCall(c *Call, newargs map[*ResultArg]*ResultArg) *Call {
 	return c1
 }
 
+func CloneArg(arg Arg) Arg {
+	return clone(arg, nil)
+}
+
 func clone(arg Arg, newargs map[*ResultArg]*ResultArg) Arg {
 	var arg1 Arg
 	switch a := arg.(type) {
diff --git a/prog/prog.go b/prog/prog.go
index f93293b64..da6f158bc 100644
--- a/prog/prog.go
+++ b/prog/prog.go
@@ -354,6 +354,9 @@ func (p *Prog) insertBefore(c *Call, calls []*Call) {
 
 // replaceArg replaces arg with arg1 in a program.
 func replaceArg(arg, arg1 Arg) {
+	if arg == arg1 {
+		panic("replacing an argument with itself")
+	}
 	switch a := arg.(type) {
 	case *ConstArg:
 		*a = *arg1.(*ConstArg)